Co-reporter:Guangda Niu;Wenzhe Li;Jiangwei Li;Xingyao Liang
RSC Advances (2011-Present) 2017 vol. 7(Issue 28) pp:17473-17479
Publication Date(Web):2017/03/17
DOI:10.1039/C6RA28501E
Organic–inorganic hybrid perovskite solar cells are found to be sensitive to moisture, oxygen, UV light, light soaking, heat, electric field, etc. Among all these factors, thermal stability is one of the most challenging concerns affecting PSCs stability, since it is hard to avoid a temperature increase for solar cells during operation. In this work, we systematically studied the thermal stability of CsxMA1−xPbI3 film and solar cells. The introduction of Cs into the precursor solution would inevitably accelerate the film deposition rate, resulting in decreased grain size and more Cs atoms in the film than in the precursors. The study on thermal stability illustrated that perovskite degradation was highly related to the amount of oxygen in the air. A small amount of Cs doping (x = 0.09) was beneficial for better thermal stability. In addition, Cs doping also enhanced the device performance. The improvement of short-circuit currents came from the increased film thickness, which was due to the faster deposition rate for Cs doped samples. Besides, Cs doping was vital to suppress the trap states in the film since the trap states were related to halide deficiency during thermal annealing. At last, the final performance of Cs0.09MA0.91PbI3 reached 18.1%, with a JSC of 22.57 mA cm−2, VOC of 1.06 V, FF of 0.76.
Co-reporter:Nan Li;Changmei Cheng;Hainan Wei;Hongbin Liu;Xiaosong Li;Wenzhe Li
RSC Advances (2011-Present) 2017 vol. 7(Issue 67) pp:42105-42112
Publication Date(Web):2017/08/29
DOI:10.1039/C7RA07514F
The moisture instability of perovskite materials especially under illumination has engendered severe hindrance toward future industrial applications for high-efficiency and stable perovskite solar cells. Here, we designed and synthesized a series of hydrophobic alkyl bisphosphonic molecules which served as interfacial layers between a perovskite and PC61BM to improve the moisture and light-stability of the inverted PVSCs. The steric arrangement of the bisphosphonic molecules suppressed the infiltration of moisture and oxygen inside the perovskite film under humidity and continuous illumination, and decreased the loss of halide and methylammonium ions as revealed by the lower PbI2 and Pb0 in the film. When exposed to 50–60% RH and continuous AM1.5G illumination, devices after undergoing interfacial treatment retained 70% of the initial power conversion efficiency, while the control device totally failed, suggesting markedly improved moisture and light-stability by the interfacial engineering. Moreover, the treated devices showed almost no degradation after being stored in an ambient atmosphere for 300 h.
Co-reporter:Qingshun Dong, Yantao Shi, Chunyang Zhang, Yukun Wu, Liduo Wang
Nano Energy 2017 Volume 40(Volume 40) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.nanoen.2017.08.041
•The whole fabrication process of crystallized SnO2 ETLs below 80 °C is realized using sol–gel route for the first time.•Participation of atmosphere O2 and H2O by refluxing is crucial for SnO2 crystallization in solution at low temperature.•This SnO2 ETLs endow planar PSCs high PCEs of 19.20% and 16.11% on rigid and flexible substrates, respectively.•Due to a large band gap (4.13 eV), SnO2-ETLs-based PSCs show superior UV light stability.In fabrication of SnO2 electron transfer layer (ETL) via traditional solution routes, the strong dependence of film crystallization on high temperature annealing or robust thermal treatment makes it challengeable to prepare crystallized SnO2 ETLs at low temperature (< 150 °C). Here, we put forward a sol-gel route by which the whole fabrication process of crystallized SnO2 ETL below 80 °C is realized for the first time. In the new route, participation of atmosphere O2 and H2O by refluxing is crucial as it can greatly promote Sn2+ oxidation and controlled hydrolysis in SnCl2·2H2O alcohol solution, in turn opening up an energetically favorable pathway for SnO2 crystallization at low temperature. Systematical investigations reveal that SnO2 ETLs have high conductivity and transmittance and appropriate energy band level, by which PSCs obtain superior photovoltaic performance, with a champion power conversion efficiency (PCE) and steady-state PCE of 19.20% and 18.48% achieved, respectively, much higher than that of the devices using high temperature annealed TiO2 ETLs (16.61% and 15.03%). The SnO2-ETL-based flexible PSCs also attain a high PCE up to 16.11% and among the highest records of flexible PSCs. Due to a larger band gap, SnO2-ETLs-based PSCs show superior UV resistance against high intensity UV light irradiation.Low temperature fabrication of SnO2 electron transfer layer (ETL) below 80 °C is realized by synthesis of SnO2 nanocrystals through an energetically favorable wet chemical route. The SnO2-ETLs with high conductivity and transmittance, appropriate band edge and wide band gap endow planar PSCs with high efficiencies and superb UV resistance.Download high-res image (178KB)Download full-size image
Co-reporter:Qingshun Dong 董庆顺;Yuan Xue 薛源;Shi Wang 王适 王立铎
Science China Materials 2017 Volume 60( Issue 10) pp:963-976
Publication Date(Web):14 September 2017
DOI:10.1007/s40843-017-9096-2
Here, the interfacial synergism of discontinuous spot shaped SnO2 and TiO2 mesoporous nanocomposite as electron transfer layer (ETL) underlayer is presented in highly efficient mesoscopic perovskite solar cells (M-PSCs). Based on this new strategy, strong charge recombination observed in previous SnO2-based ETLs is suppressed to a great extent as the pathways of charge recombination and energy loss are blocked effectively. Meanwhile, the internal series resistance of entire M-PSC is decreased remarkably. The new ETL is more kinetically favorable to electron transfer and thus results in significant photovoltaic improvement and alleviated hysteresis effect of M-PSCs.本文采用点分布SnO2和TiO2介孔层中的纳米粒子组成的“协同层”作为高效介孔钙钛矿太阳能电池的电子传输层衬层. 基于该新策略, 电荷复合和能量损失路径被有效阻隔, 使得之前报道的SnO2基电子传输层介孔钙钛矿太阳能电池中的强烈电荷复合被有效抑制. 同时, 整个介孔钙钛矿太阳能电池的串联电阻显著降低. 新型的电子传输层动力学上更有利的电子传输有效提升了介孔钙钛矿太阳能电池的光伏性能, 并明显抑制了电池的回滞.
Co-reporter:Jiangwei Li;Qingshun Dong;Nan Li
Advanced Energy Materials 2017 Volume 7(Issue 14) pp:
Publication Date(Web):2017/07/01
DOI:10.1002/aenm.201602922
Perovskite solar cells (PSCs) have recently demonstrated high efficiencies of over 22%, but the thermal stability is still a major challenge for commercialization. In this work, the thermal degradation process of the inverted structured PSCs induced by the silver electrode is thoroughly investigated. Elemental depth profiles indicate that iodide and methylammonium ions diffuse through the electron-trasnporting layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the ions extraction. Variations on the morphology and current mapping of the MAPbI3 thin films upon thermal treatment reveal that the loss of ions occurs at the grain boundaries and leads to the reconstruction of grain domains. Consequently, the deteriorated MAPbI3 thin film, the poor electron extraction, and the generation of AgI barrier result in the degradation of efficiencies. These direct evidences provide in-depth understanding of the effect of thermal stress on the devices, offering both experimental support and theoretical guidance for the improvement on the thermal stability of the inverted PSCs.
Co-reporter:Nan Li;Zonglong Zhu;Qingshun Dong;Jiangwei Li;Zhanlue Yang;Chu-Chen Chueh;Alex K.-Y. Jen
Advanced Materials Interfaces 2017 Volume 4(Issue 20) pp:
Publication Date(Web):2017/10/01
DOI:10.1002/admi.201700598
AbstractThe compositional perovskites have attracted broad attention due to the improved photovoltaic performance and enhanced stability compared with the single cation perovskite, such as methylammonium lead iodide and formamidinium lead iodide. In this study, the moisture stability of the widely used cesium and bromide-containing mixed perovskites is carefully studied by characterizing the morphology, crystallization, and device performance before and after the exposure to moisture. Though the mixed perovskites possess strong resistance to moisture in the ambient air, a rapid degradation is observed when the perovskites are exposed to a high relative humidity (RH) up to 70%. The degradation is evidenced by the obvious appearance of CsPbI3 phase along with needle-like morphology after several hours' storage in 70% RH. Moreover, to suppress the erosion of perovskites by the high-level moisture, an interfacial engineering is introduced with phenylethylammonium iodide (PEAI). The PEAI passivation not only shows a retarded degradation but also delivers an enhanced photovoltaic performance from 13% to >17% with much improved stability under high-level moisture. The results imply the efficacy of interfacial engineering in fabricating high-efficiency and stable perovskite solar cells.
Co-reporter:Jiangwei Li, Guangda Niu, Wenzhe Li, Kun Cao, Mingkui Wang and Liduo Wang
Nanoscale 2016 vol. 8(Issue 29) pp:14163-14170
Publication Date(Web):22 Jun 2016
DOI:10.1039/C6NR03359H
Perovskite solar cells (PSCs) with hole-conductor-free mesoscopic architecture have shown superb stability and great potential in practical application. The printable carbon counter electrodes take full responsibility of extracting holes from the active CH3NH3PbI3 absorbers. However, an in depth study of the CH3NH3PbI3/C interface properties, such as the structural formation process and the effect of interfacial conditions on hole extraction, is still lacking. Herein, we present, for the first time, an insight into the spatial confinement induced CH3NH3PbI3/C interface formation by in situ photoluminescence observations during the crystallization process of CH3NH3PbI3. The derived reaction kinetics allows a quantitative description of the perovskite formation process. In addition, we found that the interfacial contact between carbon and perovskite was dominant for hole extraction efficiency and associated with the photovoltaic parameter of short circuit current density (JSC). Consequently, we conducted a solvent vapor assisted process of PbI2 diffusion to carefully control the CH3NH3PbI3/C interface with less unreacted PbI2 barrier. The improvement of interface conditions thereby contributes to a high hole extraction proved by the charge extraction resistance and PL lifetime change, resulting in the increased JSC valve.
Co-reporter:Wenzhe Li, Jiangwei Li, Guangda Niu and Liduo Wang
Journal of Materials Chemistry A 2016 vol. 4(Issue 30) pp:11688-11695
Publication Date(Web):16 Dec 2015
DOI:10.1039/C5TA09165A
The interface modification of perovskite thin films has shown great potential to boost the performance of perovskite solar cells during the last few years. Here we demonstrate that cesium chloride (CsCl) as crystal seeds can markedly enhance the coverage of the CH3NH3PbI3−xClx absorber layer on TiO2 in planar heterojunction solar cells, thus boosting the power conversion efficiency (PCE) to 16.8%, with a fill factor (FF) of 0.79. Also, the introduction of CsCl significantly improved the stability of CH3NH3PbI3−xClx under ultra violet (UV) irradiation, which has been verified by XRD, XPS and SEM measurements. The CsCl-treated devices maintained 70% of the original PCE after a prolonged intensive UV irradiation of 200 min while the untreated devices being almost exhausted. Furthermore, we proposed the mechanism concerning CsCl as the modification layer to improve the UV-induced stability issue of perovskite solar cells.
Co-reporter:Wenzhe Li, Jiandong Fan, Jiangwei Li, Guangda Niu, Yaohua Mai, and Liduo Wang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 44) pp:30107
Publication Date(Web):October 14, 2016
DOI:10.1021/acsami.6b09532
Currently, the potential mechanism of the solvent-assisted crystallization for mixed cations perovskite thin film (FAxMA1–xPbI3) prepared via two-step solution-process still remains obscure. Here, we clarified the molecular-competing-reacted process of NH2CH═NH2I (FAI) and CH3NH3I (MAI) with PbI2(DMSO)x complex in dimethyl sulfoxide (DMSO) and diethyl ether (DE) catalytic solvent system in the sequential two-step solution-process. The microscopic dynamics was characterized via the characterizations of in situ photoluminescence spectra. In addition, we found that the thermal stability of the perovskite films suffered from the residual solvent with high boiling point, for example, DMSO. The further DE treatment could promote the volatility process of DMSO and accelerate the crystallization process of perovskite films. The highest PCE over 19% with slight hysteresis effect was eventually obtained with a reproducible FA0.88MA0.12PbI3 solar cell, which displayed a constant power output within 100 s upon light soaking and stable PCE output within 30 d in the thermal stability test.Keywords: perovskite solar cells; solvent engineering; thermal stability; thin films; two-step process
Co-reporter:Guangda Niu, Hongde Yu, Jiangwei Li, Dong Wang, Liduo Wang
Nano Energy 2016 Volume 27() pp:87-94
Publication Date(Web):September 2016
DOI:10.1016/j.nanoen.2016.06.053
•Ultra-smooth perovskite films oriented along <112>/<200> directions is fabricated.•Preferentially precipitated Cs-doped perovskite is responsible for the orientation.•The special orientation improved the charge transfer and suppressed the trap states.•We achieved a PCE of 17.6%, with improvements in stability under UV irradiance.Solar cells based on organic inorganic hybrid metal halide perovskites have exhibited a rapid increase of power conversion efficiency (PCE). Perovskite solar cells involving mixed cations, especially recently reported Cs doping, have shown huge potential to improve PCE as well as device stability. However, when doping Cs into CH3NH3PbI3 (MAPbI3) and [HC(NH2)2]3PbI3 (FAPbI3), CsPbI3 could segregate from the perovskite phase, affecting the performance negatively. In addition, despite improved charge transfer was predicted for oriented film along <112>/<200> directions, the fabrication is still on the way and rarely reported. Herein, an ultra-smooth perovskite film oriented along <112>/<200> directions is created for the first time, with a homogeneous tetragonal phase of (MAPbI3)1−x(CsPbBr3)x. The preferentially precipitated heavily Cs-doped perovskite, and the lowered surface energy of (112) and (200) planes, verified by DFT calculations, are responsible for the orientation. The improved charge transfer and suppressed trap states in the oriented film substantially improved the performance. Upon an optimal doping ratio of 0.1, a PCE of 17.6% was achieved, together with remarkable improvements in stability under UV irradiance and in ambient atmosphere.
Co-reporter:Guangda Niu 牛广达;Wenzhe Li 李闻哲;Jiangwei Li 李江伟 王立铎
Science China Materials 2016 Volume 59( Issue 9) pp:728-742
Publication Date(Web):2016 September
DOI:10.1007/s40843-016-5094-6
Organic-inorganic hybrid halide perovskite materials have been a suitable active layer in solar cells due to the extraordinary photonic and electronic properties. Perovskite solar cells (PSCs), no matter conventional structure or inverted structure, contain several key interfaces, including electrode/electron transport materials (ETM) interface, ETM/perovskite interface, perovskite/hole transport materials (HTM) interface, HTM/electrode interface. The interface is vital to the overall performance of the devices, since the exciton formation, dissociation, and recombination are directly related to the interface. Moreover, the degradation of devices is also highly sensitive to the interface. As a result, the deep understanding of the interfacial charge transfer and corresponding interfacial engineering is extremely important to achieve high-performance and high-stability PSCs. This review mainly focuses on the recent progress of interfacial engineering in PSCs, including conventional structured PSCs, PSCs employing carbon counter electrode, and inverted structured PSCs.有机-无机杂化钙钛矿由于其优异的电学及光学性质, 成为制备太阳电池吸光层的理想材料. 无论反式还是正式结构的钙钛矿太阳电池, 均包含以下几个关键界面: 电极/电子传输层界面、电子传输层/钙钛矿界面、钙钛矿/空穴传输层界面、空穴传输层/电极界面. 这些界面的性质对于电池性能至关重要, 因为激子的形成、分离及复合都直接决定于这些界面. 此外, 器件的稳定性也受界面性质的影响. 因此, 界面电荷转移以及相应的界面修饰对于制备高效率、高稳定性电池器件具有重要助益. 本论文将侧重综述近期在钙钛矿电池领域关于界面修饰问题的重大突破与进展.
Co-reporter:Wenzhe Li; Jiandong Fan; Jiangwei Li; Yaohua Mai
Journal of the American Chemical Society 2015 Volume 137(Issue 32) pp:10399-10405
Publication Date(Web):August 6, 2015
DOI:10.1021/jacs.5b06444
The highly developed crystallization process with respect to perovskite thin films is favorable for efficient solar cells. Here, an innovative intermolecular self-assembly approach was employed to retard the crystallization of PbI2 in dimethylformamide (DMF) by additional solvent of dimethyl sulfoxide (DMSO), which was proved to be capable of coordinating with PbI2 by coordinate covalent bond. The obtained PbI2(DMSO)x (0 ≤ x ≤ 1.86) complexes tend to be closely packed by means of intermolecular self-assembly. Afterward, an intramolecular exchange of DMSO with CH3NH3I (MAI) enabled the complexes to deform their shape and finally to reorganize to be an ultraflat and dense thin film of CH3NH3PbI3. The controllable grain morphology of perovskite thin film allows obtaining a power conversion efficiency (PCE) above 17% and a stabilized power output above 16% within 240 s by controlling DMSO species in the complex–precursor system (CPS). The present study gives a reproductive and facile strategy toward high quality of perovskite thin films and efficient solar cells.
Co-reporter:Jiangwei Li, Wenzhe Li, Haopeng Dong, Nan Li, Xudong Guo and Liduo Wang
Journal of Materials Chemistry A 2015 vol. 3(Issue 16) pp:8882-8889
Publication Date(Web):16 Mar 2015
DOI:10.1039/C4TA05762G
Lithium salts have been important additives to the hole-transport materials of solid-state hybrid perovskite solar cells to achieve higher hole mobility. However, the observed intercalation of Li+ into TiO2 was demonstrated to decrease the open-circuit voltage (VOC) of the cells. In this work, spinel lithium titanate Li4Ti5O12 (LTO) was used to alleviate this issue by consuming Li+ prior to the contact of Li+ with TiO2 at the interface between sensitized TiO2 and the hole-transport layer through the chemical insertion of Li+ into LTO. Raman and X-ray photoelectron spectroscopy results confirmed the insertion of Li+ into LTO. A Li+ insertion peak in cyclic voltammetry and an increased density of states of TiO2 revealed the role of LTO as a Li+ separator to protect the TiO2 photoanode, providing the mechanism of VOC increase for LTO modification. Electrochemical impedance spectroscopy revealed that LTO modification markedly reduced carrier recombination, improving the fill factor of the devices. Overall, the conversion efficiencies of the devices were significantly increased with a maximum efficiency of 15.1% by addition of LTO. The strategy of using LTO as a multifunctional modifier broadens the scope of interface engineering in solar cells.
Co-reporter:Guangda Niu, Xudong Guo and Liduo Wang
Journal of Materials Chemistry A 2015 vol. 3(Issue 17) pp:8970-8980
Publication Date(Web):03 Dec 2014
DOI:10.1039/C4TA04994B
In recent years, the record efficiency of perovskite solar cells (PSCs) has been updated from 9.7% to 20.1%. However, there has been very little study of the issue of stability, which restricts the outdoor application of PSCs. The issues of the degradation of perovskite and the stability of PSC devices should be urgently addressed to achieve good reproducibility and long lifetimes for PSCs with high conversion efficiency. Without studies on stability, exciting achievements cannot be transferred from the laboratory to industry and outdoor applications. In order to improve their stability, a basic understanding of the degradation process of PSCs in different conditions should be acquired via thorough study. This review summarizes recent studies of the relationship of the chemical stability of PSCs with their environment (oxygen and moisture, UV light, solution process, temperature) and corresponding possible solutions.
Co-reporter:H. P. Dong, Y. Li, S. F. Wang, W. Z. Li, N. Li, X. D. Guo and L. D. Wang
Journal of Materials Chemistry A 2015 vol. 3(Issue 18) pp:9999-10004
Publication Date(Web):27 Mar 2015
DOI:10.1039/C5TA00407A
Interface engineering is an important and efficient way to further improve the conversion efficiency of perovskite solar cells. In this study, we report the modification of the electron transport layer (ETL) using a thin layer of PEO. Characterizations showed that PEO was uniformly coated on top of the original TiOx ETL, without resulting in an evident change of the surface morphology, hydrophilic ability or transparency. With the interface dipole formed at the interface, the work function of the ETL greatly decreased. Compared with devices with TiOx only, devices based on the modified ETL gave a nearly 15% enhancement to the overall conversion efficiency, with both Voc and Jsc improved. Further studies showed that the improved performance could mainly be attributed to the better retardation of back recombination and the enhanced electron collection efficiency by means of the PEO thin layer modification.
Co-reporter:Nan Li, Haoyuan Li, Yu Li, Shufeng Wang and Liduo Wang
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 37) pp:24092-24097
Publication Date(Web):20 Aug 2015
DOI:10.1039/C5CP03803K
In meso-superstructured solar cells (MSSCs), the state-of-the-art perovskite acts as both the light harvester and electron transporter due to its ambipolar properties. The inefficient pore filling and infiltration of perovskite directly affect the continuous distribution of perovskite in mesoporous Al2O3, resulting in discontinuous carrier transport in the mesoporous structure and insufficient electron injection to the compact TiO2 layer. Herein, we introduce a simple pre-spin-coating process to improve the infiltration and pore filling of perovskite, which results in higher light absorption and enhanced electron injection, as seen in UV-vis spectra and photoluminescence (PL) spectra, respectively. We first apply time of flight (TOF) experiments to characterize charge transport in MSSCs, and the results reveal that more continuous charge transport pathways are formed with the pre-spin-coating process. This effective method, with ease of processing, demonstrates obviously improved photocurrents, reaching an efficiency as high as 14%, and promotes the application of lead halide perovskite materials in the photovoltaics field.
Co-reporter:Xudong Guo;Haopeng Dong;Wenzhe Li;Nan Li ; Liduo Wang
ChemPhysChem 2015 Volume 16( Issue 8) pp:1727-1732
Publication Date(Web):
DOI:10.1002/cphc.201500163
Abstract
A multifunctional magnesium oxide (MgO) layer was successfully introduced into perovskite solar cells (PSCs) to enhance their performance. MgO was coated onto the surface of mesoporous TiO2 by the decomposition of magnesium acetate and, therefore, could block contact between the perovskite and TiO2. X-ray photoelectron spectroscopy and infrared spectroscopy showed that the amount of H2O/hydroxyl absorbed on the TiO2 decreased after MgO modification. The UV/Vis absorption spectra of the perovskite with MgO modification revealed an enhanced photoelectric performance compared with that of unmodified perovskite after UV illumination. In addition to the photocurrent, the photovoltage and fill factor also showed an enhancement after modification, which resulted in an increase in the overall efficiency of the cell from 9.6 to 13.9 %. Electrochemical impedance spectroscopy (EIS) confirmed that MgO acts as an insulating layer to reduce charge recombination.
Co-reporter:Guangda Niu, Wenzhe Li, Fanqi Meng, Liduo Wang, Haopeng Dong and Yong Qiu
Journal of Materials Chemistry A 2014 vol. 2(Issue 3) pp:705-710
Publication Date(Web):04 Nov 2013
DOI:10.1039/C3TA13606J
Degradation of perovskite has been a big problem in all-solid-state perovskite solar cells, although many researchers mainly focus on the high efficiency of these solar cells. This paper studies the stability of CH3NH3PbI3 films and finds that CH3NH3PbI3 is sensitive to moisture. The degradation reaction is proposed according to UV-Vis spectra and XRD results. In order to improve the degradation of CH3NH3PbI3, we introduce aluminum oxide as a post-modification material into all-solid-state perovskite solar cells for the first time. UV-Vis spectra show that Al2O3 modification could maintain the absorption of CH3NH3PbI3 after degradation. XRD results reveal that Al2O3 could protect perovskite from degradation. Moreover, the device post-modified by Al2O3 has shown more brilliant stability than that without modification when exposed to moisture. EIS results and dark current illustrate that the modification increased interface resistance in the dark, indicating the restrained electron recombination process.
Co-reporter:Nan Li, Haopeng Dong, Hua Dong, Jiaoli Li, Wenzhe Li, Guangda Niu, Xudong Guo, Zhaoxin Wu and Liduo Wang
Journal of Materials Chemistry A 2014 vol. 2(Issue 36) pp:14973-14978
Publication Date(Web):14 Jul 2014
DOI:10.1039/C4TA02921F
In this study, the crucial role of perovskites capping layers in the TiO2/CH3NH3PbI3 hybrid solar cells is investigated. The capping layers are realized by controlling the concentration of PbI2 solutions in the sequential deposition process. The morphologies of the active layers are studied by high-resolution scanning electron microscopy (HR-SEM). The amount of perovskites in capping layers increases with the concentration of PbI2 solution, and the coverage of perovskite capping layers on TiO2 films is better developed. Except for the correlation between photocurrents and coverages of perovskite proposed by Snaith, we revealed a more detailed relationship between the photovoltaic performances and perovskite capping layers. It is noteworthy that UV-vis absorption increased with perovskites in capping layers. Moreover, according to the diffuse reflection spectra, light scattering, which is beneficial for the conversion efficiency of photons to electrons by directly preventing most of the incident light from transmitting out, is also enhanced due to both the emergence of larger-size particles in the capping layers and the higher effective dielectric coefficient. All of the aforementioned aspects result in high photocurrents up to 20.6 mA cm−2. Efficiency as high as 10.3% is ultimately achieved by a simple control of PbI2 concentration in the sequential deposition process.
Co-reporter:Rui Gao, Yixiu Cui, Xiaojiang Liu, Liduo Wang and Guozhong Cao
Journal of Materials Chemistry A 2014 vol. 2(Issue 13) pp:4765-4770
Publication Date(Web):14 Jan 2014
DOI:10.1039/C3TA15276F
A novel ZnO nanorod/nanoparticle (NR/NP) hierarchical structure on a zinc foil has been fabricated through a chemical bath deposition method. When used as a flexible photoanode for DSSCs, such a structure demonstrated enhanced dye-loading and electron lifetime as compared to the NR structure. It also retarded the charge recombination while maintaining the electron diffusion length of the NR structure. As a result, the power conversion efficiency of the DSSCs based on the NR/NP structure increased from 1.35% to 3.63% with a 169% enhancement as compared to that based on ZnO NRs.
Co-reporter:Wenzhe Li, Haopeng Dong, Xudong Guo, Nan Li, Jiangwei Li, Guangda Niu and Liduo Wang
Journal of Materials Chemistry A 2014 vol. 2(Issue 47) pp:20105-20111
Publication Date(Web):2014/10/16
DOI:10.1039/C4TA05196C
The interface between perovskite and the hole transport layer (HTL) is sensitive to photoelectric conversion properties. However, this study shows that the interface wettability of the HTL solution on a perovskite surface could be improved. To address this problem, graphene oxide (GO) with amphiphilic function was used to form a buffer layer between the perovskite and the HTL. After the GO modification, the contact angles of the HTL solution on the perovskite film decreased to zero degrees. X-ray photoelectron spectroscopy revealed that the GO interacts with the perovskite by forming Pb–O bonds, and Raman spectroscopy analysis revealed that the two-dimensional carbon–carbon bonds absorbed the hole transport material, 2,29,7,79-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,99-spirobifluorene (Spiro-MeOTAD) via π–π interactions. The GO layer improved the contact between the perovskite and HTL, resulting in an enhancement of the short circuit current (JSC). Moreover, using GO as an insulating buffer layer can retard charge recombination in solar cells, as revealed by EIS measured in dark conditions, leading to a significant increase in the open-circuit voltage (VOC) and the fill factor (FF). Consequently, the corresponding average efficiency greatly increased by 45.5%, from 10.0% to 14.5%. Therefore, application of GO as a dual-functional buffer layer on the perovskite layer is a useful strategy for preparing highly efficient hybrid perovskite solar cells.
Co-reporter:Wenzhe Li, Haopeng Dong, Liduo Wang, Nan Li, Xudong Guo, Jiangwei Li and Yong Qiu
Journal of Materials Chemistry A 2014 vol. 2(Issue 33) pp:13587-13592
Publication Date(Web):20 Jun 2014
DOI:10.1039/C4TA01550A
4-tert-Butylpyridine (TBP) has been an important component in hole transport layer for hybrid perovskite solar cells. However, our study shows that TBP can corrode the perovskite absorption layer (CH3NH3PbI3) and interfere with the stability of the solar cells. To address this problem, montmorillonite (MMT) was used to form a buffer layer on top of the hole transport layer. XRD results revealed that TBP was intercalated in the MMT structure and UV-vis spectroscopy analysis revealed that this structure could prevent the corrosion of the CH3NH3PbI3 layer. Moreover, the MMT buffer layer could limit charge recombination in the solar cells. A delayed corrosion led to an increased current density owing to enhanced absorption, while a reduced charge recombination led to an increased fill factor and open voltage circuit values. Consequently, the corresponding efficiency largely increased from 9.0% to 11.9%, with an improvement of 32.2%. Therefore, the application of MMT as a bifunctional buffer coating layer on the hole transport layer is a useful strategy for preparing highly efficient hybrid perovskite solar cells with anti-corrosion and delayed charge recombination properties.
Co-reporter:Rui Gao, Yixiu Cui, Xiaojiang Liu, Liduo Wang
Electrochimica Acta 2014 Volume 129() pp:85-92
Publication Date(Web):20 May 2014
DOI:10.1016/j.electacta.2014.02.081
In this paper, a photoanode of compact TiO2 film with a small specific surface area has been developed to discuss the effects of interlayer in the dye/modification material alternating assembly structure. The compact film photoanode could avoid the complexity and various influence factors of porous film as light scattering and different diffusion rates of electrolyte in the pores. It is beneficial to discuss the effects of alternating assembly structure. From the discussion based on compact TiO2 film, it was indicated that the suitable material used for the interlayer of alternating assembly structure should show relatively strong alkalinity and higher energy level than the Lowest Unoccupied Molecular Orbital (LUMO) of dye molecules. The former is easier for the absorption of a second layer of dyes, and the latter ensured the generated electrons of the second layer of dye can inject into the conduction band of TiO2. Using the obtained suitable material as interlayer of alternating assembly structure enhanced the conversion efficiency of DSCs remarkably.
Co-reporter:Guangda Niu, Nan Li, Liduo Wang, Wenzhe Li and Yong Qiu
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 34) pp:18327-18332
Publication Date(Web):11 Jul 2014
DOI:10.1039/C4CP02520B
Combined post-modification strategy of iodide ligands and wide band gap ZnS layer were employed in quantum dot sensitized solar cells. J–V curves show that the combined post-modification could improve the photoconversion efficiency compared to the single post-modification of ZnS because of the more effective passivation. CdS-sensitized and CdS/CdSe-co-sensitized solar cells both reveal that the assembly structure of QDs/I−/ZnS is more beneficial for the efficiency of solar cells than that of QDs/ZnS/I−. EIS results show that the former structure exhibit higher interface resistance and could suppress electron recombination more powerfully. XPS results reveal that the iodide ligands have different binding energy, which indicates a different coordination state of the iodide atom in these two structures. Finally, 3.28% efficiency and 18.16 mA cm−2 were achieved for CdS/CdSe QDSCs by applying this combined post-modification.
Co-reporter:Haopeng Dong, Xudong Guo, Wenzhe Li and Liduo Wang
RSC Advances 2014 vol. 4(Issue 104) pp:60131-60134
Publication Date(Web):06 Nov 2014
DOI:10.1039/C4RA08565E
Cs2CO3 has been employed as a new surface modification material for inorganic–organic hybrid perovskite solar cells. With the optimized modifying process, 14.2% power conversion efficiency (PCE) was obtained, enhanced by nearly 20% compared with the control devices. Further studies showed that the PCE improvement mainly came from the retarded back recombination.
Co-reporter:Xudong Guo, Haopeng Dong, Guangda Niu, Yong Qiu and Liduo Wang
RSC Advances 2014 vol. 4(Issue 41) pp:21294-21300
Publication Date(Web):30 Apr 2014
DOI:10.1039/C4RA03188A
In this paper, Mg doping is utilized in the synthesis of a nanosheet-based spherical structured ZnO photoanode resulting in an increased overall efficiency from 1.72% to 4.19% of quasi-solid dye-sensitized solar cells. Existence of Mg in the ZnO crystal is detected by XRD and XPS measurements. The diameter of the ZnO nanosheet-based spherical structure is obviously decreased after Mg doping, which facilitates the fabrication of ZnO films and increases the specific area leading to larger dye loading and higher photocurrent. The energy bandgap of the ZnO photoanode with and without Mg doping is investigated by UV-vis spectra and theoretical calculation based on the GAUSSIAN 09 program and an increase of the bandgap is observed after Mg doping, which leads to an increase of the conduction band position and enhances the photo-voltage of DSSCs based on Mg doped ZnO photoanodes. An electrochemical impedance spectroscopy (EIS) test also indicates that DSSCs based on Mg doped ZnO show a strengthened effect of facilitating electron transport and retarding the charge recombination.
Co-reporter:Wenzhe Li, Jiaoli Li, Liduo Wang, Guangda Niu, Rui Gao and Yong Qiu
Journal of Materials Chemistry A 2013 vol. 1(Issue 38) pp:11735-11740
Publication Date(Web):29 Jul 2013
DOI:10.1039/C3TA12240A
The method of post-modification by aluminum oxide was successfully introduced into perovskite sensitized solar cells with a liquid electrolyte. Post-modification by Al2O3 could both protect the perovskite sensitizer from corrosion by electrolyte and effectively suppressed electron recombination. The UV-vis spectra revealed an enhanced absorption especially in the long wavelength range after modification. The XRD results showed a disappeared peak of PbI2, demonstrating that the modification could effectively protect the perovskite from dissolution in the electrolyte. Stability test showed that the remaining JSC improved from 10% to 50% at a given period of time. The EIS results and dark current curves illustrated that this modification increased the interface resistance in dark, confirming that the electron recombination process was effectively restrained. Finally, the corresponding efficiency was largely increased from 3.56 to 6.00% by 68%. The strategy using aluminium oxide to post-modify a perovskite sensitized solar cell was therefore proved to be a useful tool for the optimization of perovskite sensitized solar cells.
Co-reporter:Guangda Niu, Liduo Wang, Rui Gao, Wenzhe Li, Xudong Guo, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 45) pp:19595-19600
Publication Date(Web):31 Jul 2013
DOI:10.1039/C3CP52678J
Halogen ions (I−, Br−, Cl−) were added into a colloidal solution of CdSe and PbS quantum dots (QDs) to form QDs capped with these inorganic ligands. Halogen ions attached to QDs through electrostatic interactions and the varying coordination strength between the inorganic ligands and QDs led to different degrees of redispersion and stabilization in polar solvents. Moreover, we successfully conducted electrophoretic deposition (EPD) of QDs capped with inorganic ligands. Negatively charged QDs were adsorbed onto a positively charged TiO2 anode. The assembled QDs films were used in photovoltaic devices and offered better efficiency than QDs capped with organic ligands. This work demonstrates that halogen ions are indeed promising ligands to improve the stability of QDs with inorganic ligands and the EPD method shows prospects in assembling QDs films for practical applications.
Co-reporter:Rui Gao, Zhiqiang Liang, Jianjun Tian, Qifeng Zhang, Liduo Wang, Guozhong Cao
Nano Energy 2013 Volume 2(Issue 1) pp:40-48
Publication Date(Web):January 2013
DOI:10.1016/j.nanoen.2012.07.009
A novel interface precipitation method has been developed to synthesize hierarchically structured ZnO nanocrystallite aggregates. Such synthesized ZnO nanocrystallite aggregates were demonstrated as a promising structure for high power conversion efficiency when used as photoelectrode in dye-sensitized solar cells (DSCs). In comparison with ZnO nanoparticles synthesized by conventional homogeneous precipitation method, such hierarchical structure has larger specific surface area, more efficient dye-loading and effective light scattering within the photoelectrode; all result in an increased photocurrent. Furthermore, electrochemical impedance spectroscopy study revealed that reduced charge recombination in ZnO nanocrystallite aggregates resulted in enhanced Voc. As a result, a power conversion efficiency of 5.07% with commercially available dye N719 has been obtained without applying anti-reflection coating and chemical treatment, which was more than 200% of the power conversion efficiency achieved in ZnO nanoparticles synthesized by homogeneous precipitation method in aqueous solution.Graphical abstractHighlights► Interface precipitation to synthesize aggregates of ZnO nanocrystallites. ► Enhanced DSC power conversion efficiency. ► Higher dye-loading, introduced light-scattering, less charge recombination.
Co-reporter:Guangda Niu, Liduo Wang, Rui Gao, Beibei Ma, Haopeng Dong and Yong Qiu
Journal of Materials Chemistry A 2012 vol. 22(Issue 33) pp:16914-16919
Publication Date(Web):25 Jun 2012
DOI:10.1039/C2JM32459H
In this paper, inorganic iodide ligands were used in PbS quantum dot sensitized solar cells (QDSCs) with iodide/triiodide electrolytes. Inorganic ligands are employed to replace organic ligands in QDSCs for the first time. They combined effects of passivating surface states and decreasing the interface resistance between QDs and sensitized TiO2, QDs and electrolyte. Then the corrosion of PbS QDs by triiodide in iodide/triiodide electrolytes was suppressed and electron injection and hole transfer was much easier. Stability test verified iodide ligands could prevent PbS from corrosion of iodide/triiodide electrolytes. Electrochemical impedance spectroscopy (EIS) showed that iodide ligands effectively decreased the interface resistance and improved the electron transfer. Finally, the performance with iodide ligands was significantly improved and achieved 3.7 times that of the untreated cells in efficiency.
Co-reporter:Rui Gao, Guangda Niu, Liduo Wang, Yi Geng, Beibei Ma, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 17) pp:5973-5978
Publication Date(Web):05 Mar 2012
DOI:10.1039/C2CP24137D
In this paper, 8-hydroxyquinoline aluminium (Alq3) was used in interface modification of dye-sensitized solar cells (DSCs). Alq3 was the first discovered interface modification material with combined effects of retarding charge recombination and Förster resonant energy transfer (FRET). Results of dark current curve and AC impedance showed that Alq3 could retard charge recombination in DSCs. I–V curves showed that conversion efficiency increased with Alq3 modification. Besides the interface modification effect, it was discovered that Alq3 also acted as energy relay dye with the FRET effect between itself and N3, which increased photoresponse and electron injection. The application of Alq3 with combined effects opened a new door to explore more novel multi-functional interface modification materials to improve the performance of DSCs.
Co-reporter:Haopeng Dong, Liduo Wang, Rui Gao, Beibei Ma and Yong Qiu
Journal of Materials Chemistry A 2011 vol. 21(Issue 48) pp:19389-19394
Publication Date(Web):01 Nov 2011
DOI:10.1039/C1JM14191K
ZnO
nanorod–nanoparticles (NR–NPs) hierarchical structure was prepared via a two-step hydrothermal process at 70 °C. In the hierarchical structure, ZnO nanorods prepared at step one served as the backbone for direct electron transport while ZnO nanoparticles synthesized at step two offered large surface area for dye-loading. Both reaction temperature and reaction time at step two had a significant influence on the morphology of the product. At a higher temperature, microspheres appeared above the nanorod film instead of nanoparticles surrounding the nanorods. Prolonging the reaction time to 24 h, the NR–NPs structure would transform to nanorod–nanoplants. Intensity-modulated photocurrent spectroscopy results showed that the photoanode composed of the NR–NPs hierarchical structure had an electron diffusion coefficient (Dn) much higher than that of the nanoparticles. The dye desorption results showed that the dye adsorption amount for the NR–NPs structure was as much as 250% of that for the nanorods. Compared with dye-sensitized solar cells (DSCs) based on nanorods, the incident photon-to-electron conversion efficiency of the DSCs based on NR–NPs hierarchical structure improved remarkably. Under AM 1.5G illumination (100 mW cm−2), the power conversion efficiency of DSCs based on photoanodes composed of NR–NPs hierarchical structure exhibited a significant improvement (more than 120%) compared with that of ZnO nanorods.
Co-reporter:Yantao Shi, Haopeng Dong, Liduo Wang, Chun Zhan, Rui Gao and Yong Qiu
Journal of Materials Chemistry A 2011 vol. 21(Issue 9) pp:3183-3188
Publication Date(Web):24 Jan 2011
DOI:10.1039/C0JM03742G
In this paper, by altering reactants concentration, ZnO spindles with different sizes were controllably prepared through a fast precipitation process in aqueous solution. Some important characteristics such as specific area, macropore structure, light scattering and electron transport properties of the photoanodes were systematically investigated. The results showed that photoanodes composed of small-sized ZnO spindles had a larger specific area for dye-loading, while the large-sized ZnO spindles had more efficient light scattering and electron transport properties. Furthermore, to combine the advantages of different sized ZnO particles, composite photoanodes were fabricated by mixing together ZnO spindles of different sizes. Compared with the dye sensitized solar cells (DSCs) using photoanodes with single-sized ZnO spindles, the devices based on composite photoanodes showed a higher short-circuit photocurrent density without obvious decrease in open-circuit voltage and fill factor. As a result, photovoltaic performances of the DSCs were improved remarkably.
Co-reporter:Beibei Ma, Liduo Wang, Haopeng Dong, Rui Gao, Yi Geng, Yifeng Zhu and Yong Qiu
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 7) pp:2656-2658
Publication Date(Web):16 Dec 2010
DOI:10.1039/C0CP02415E
PbS QDs have been synthesized by an in situ photocatalysis method using the photocatalytic activity of nanocrystalline TiO2 films. Both the photovoltaic response and size of the synthesized PbS QDs were analyzed. Compared with the conventional synthesis route, this method is simpler and produces less waste.
Co-reporter:Rui Gao, Liduo Wang, Yi Geng, Beibei Ma, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 22) pp:10635-10640
Publication Date(Web):05 May 2011
DOI:10.1039/C0CP02820G
In this paper, the interface modification effects of 4-tertbutylpyridine (TBP), especially the interaction with dye molecules, were discussed. The results of FTIR showed that TBP interacted with dye molecules, in addition to its interaction with the TiO2 film. Reaction between N3 and TBP by the interaction force of the H atom in the –COOH group of N3 and the N atom of TBP could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. Furthermore, the results of cyclic voltammograms and UV-vis absorption edge revealed the interaction between TBP and dye molecules could cause the energy level of the dye molecules to change, influencing the electron injection efficiency in DSCs. The IPCE results indicated that with TBP modification, the injection efficiency decreased, but the electron collection efficiency was enhanced.
Co-reporter:Yi Geng, Yantao Shi, Liduo Wang, Beibei Ma, Rui Gao, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 6) pp:2417-2421
Publication Date(Web):25 Nov 2010
DOI:10.1039/C0CP01866J
Montmorillonite (MMT) added to electrolytes has been reported in the literature to facilitate the transport of I−/I3−, and improve the ionic conductivity and consequent photocurrent of dye-sensitized solar cells (DSCs). This paper firstly observes, investigates and reports that MMT addition to a poly(ethylene oxide) (PEO)-based gel electrolyte not only improves the ionic conductivity of the gel electrolyte, but also increases the photovoltage and decreases the dark current. From the results of electrochemical impedance spectroscopy (EIS) and transient photovoltage spectra, we evidence that MMT in the polymer gel electrolyte can efficiently retard the charge recombination that occurs at the TiO2/dye/electrolyte interfaces.
Co-reporter:Rui Gao ; Liduo Wang ; Yi Geng ; Beibei Ma ; Yifeng Zhu ; Haopeng Dong ;Yong Qiu
The Journal of Physical Chemistry C 2011 Volume 115(Issue 36) pp:17986-17992
Publication Date(Web):July 14, 2011
DOI:10.1021/jp204466h
In this paper, interface effects of N-methyl-benzimidazole (NMBI) and a novel intercalation composite of NMBI and montmorillonite (MMT) were studied. The intercalation composite showed better interface modification effects than NMBI individually. The FTIR spectra results showed interaction between N3 and NMBI could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. However, the results of cyclic voltammograms and UV–vis absorption edge revealed the interaction between NMBI and dye molecules could cause the lowest unoccupied molecular orbital (LUMO) level of the dye molecule to drop, decreasing the electron injection efficiency. It decreased the Jsc of dye-sensitized solar cells (DSCs). The intercalation composite could remedy the disadvantage of NMBI and obtain strengthened interface effects. The photocurrent–voltage (I–V) curve showed that, with the modification of this intercalation nanocomposite, the Jsc of the devices increased, showing that the disadvantage caused by NMBI was improved. Besides, results of the dark current curve and transient photovoltage spectra showed the NMBI–MMT intercalation composite modification retarded charge recombination more effectively than using NMBI individually. An electrochemical impedance spectroscopy (EIS) test also indicated that modification of the NMBI–MMT intercalation composite showed a strengthened effect of retarding the charge recombination. Furthermore, the results of intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) tests also showed that the interface modification of the NMBI–MMT intercalation composite enhanced the electron transportation and lifetime in DSCs more than using NMBI individually.
Co-reporter:Yantao Shi;Chun Zhan;Beibei Ma;Rui Gao;Yifeng Zhu ;Yong Qiu
Advanced Functional Materials 2010 Volume 20( Issue 3) pp:437-444
Publication Date(Web):
DOI:10.1002/adfm.200901318
Abstract
In this paper, a novel hierarchically structured ZnO photoanode for use in quasi-solid state dye-sensitized solar cells (DSCs) is presented. The film is composed of polydisperse spindle-shaped ZnO particles that are prepared through direct precipitation of zinc acetate in aqueous solution. Without additional pore-forming agents, the microporous structure is well constructed through the packing of polydisperse ZnO particles. In the film, small ZnO particles are able to improve interparticle connectivity and offer a large internal surface area for sufficient dye-adsorption; on the other hand, particles of larger size can enhance the occurrence of light-scattering and introduce micropores for the permeation of quasi-solid state electrolytes. Meanwhile, morphologies, particle size, and specific areas of the products are controlled by altering the reactant concentration and synthetic temperature. Combined with a highly viscous polymer gel electrolyte, a device based on this ZnO photoanode shows high conversion efficiencies, 4.0% and 7.0%, under 100 and 30 mW cm−2 illumination, respectively. Finally, the unsealed device is demonstrated to remain above 90% of its initial conversion efficiency after 7 days, showing excellent stability.
Co-reporter:Yifeng Zhu, Yantao Shi, Liduo Wang, Rui Gao, Beibei Ma, Yi Geng and Yong Qiu
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 45) pp:15001-15006
Publication Date(Web):2010/10/18
DOI:10.1039/C004372A
The interface modification effect within quasi-solid dye-sensitized solar cells and the photovoltaic performance were investigated after the introduction of Mg(OOCCH3)2 as an additive into a polymer gel electrolyte. Electrochemical impedance spectroscopy showed that the addition of Mg(OOCCH3)2 into the polymer gel electrolyte can efficiently retard charge recombination at the TiO2/electrolyte interface. Mg(OOCCH3)2 in the electrolyte can also contribute to the enhancement of the incident photon-to-electron conversion efficiency by modifying the dye molecules. This results in an improvement in the photovoltage and photocurrent due to a barrier layer at the TiO2/electrolyte interface and the promotion of charge injection at the dye/TiO2 interface, respectively. Photovoltaic measurements reveal that a conversion efficiency enhancement from 4.05% to 4.96% under 100 mW cm−2 is obtained after the amount of Mg(OOCCH3)2 added was optimized.
Co-reporter:BeiBei Ma;Rui Gao;YiFeng Zhu;YanTao Shi;Yi Geng
Science China Chemistry 2010 Volume 53( Issue 8) pp:1669-1678
Publication Date(Web):2010 August
DOI:10.1007/s11426-010-4042-8
Interface modification on the TiO2/dye/electrolyte interface of dye-sensitized solar cells (DSCs) is one of the most effective approaches to suppress the charge recombination, improve electron injection and transportation, and thus ameliorate the conversion efficiency and stability of DSCs. Conventional research focusing on the photoanodes interface modification before sensitization in dye-sensitized solar cells has been carried out and reviewed. However, recent studies showed that post-modification after sensitization of the TiO2 electrode also plays a significant role on the TiO2/dye/electrolyte interface. This post-modification using the immersing method could deprotonate dye molecules, prohibit the dye aggregation and retard the recombination reaction. As a result, it has great influence on the devices’ photovoltaic performance. This interface modification could also provide an approach to broaden the response of the solar spectrum by introducing an alternative assembling structure. An in-situ meaning of using a co-adsorbent is employed to modify the interface in the DSCs, which could retard the aggregation of the dye molecules and enhance the conversion efficiency. In addition, electrolyte additives can be used to modify the TiO2/dye/electrolyte interface through some unique mechanisms. Based on the background of interface modification of photoanodes before sensitization, this review introduces various interface modifications after sensitization of dye-sensitized solar cells and their mechanisms.
Co-reporter:Rui Gao, Liduo Wang, Beibei Ma, Chun Zhan and Yong Qiu
Langmuir 2010 Volume 26(Issue 4) pp:2460-2465
Publication Date(Web):October 26, 2009
DOI:10.1021/la902688a
In this paper, a simple yet efficient method is proposed to improve the performance of dye-sensitized solar cells (DSCs) by modification after sensitization using Mg(OOCCH3)2. With modification of Mg(OOCCH3)2, a blue shift of the absorption peak and optical band gap were observed in the UV−vis spectrum. As shown in the Fourier transform infrared spectrum, the intermolecular hydrogen bonding of N3 dye, which caused the aggregation of dye molecules, was weakened. As shown in the I−V characteristic, the conversion efficiency of the DSCs was improved by the treatment of Mg(OOCCH3)2. Furthermore, the charge recombination was retarded as evidenced by the decreased dark current and the slowed decay rate of the dye excited state, which were characterized by the I−V curve in dark and transient photovoltage spectra. The mechanism of this modification process was also proposed further. Modification with Mg(OOCCH3)2 facilitated the electron injection from the dye molecule to the conductive band of TiO2 by raising the excited state energy level of the dye molecule. This energy level rising was evidenced by the results of the cyclic voltammetry test and the blue shift of the optical band gap. Furthermore, Mg(OOCCH3)2 worked as an insulating barrier layer at the sensitized TiO2/electrolyte interface, thereby retarding the charge recombination in DSCs.
Co-reporter:Yantao Shi, Chun Zhan, Liduo Wang, Beibei Ma, Rui Gao, Yifeng Zhu and Yong Qiu
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 21) pp:4230-4235
Publication Date(Web):23 Mar 2009
DOI:10.1039/B901003C
The electrically conductive function of high-molecular weight poly(ethylene oxide) (PEO) (Mw = 2 × 106 g mol−1) was investigated when it was used to gelate liquid electrolyte to fabricate a series of polymer gel electrolytes for dye-sensitized solar cells (DSCs). With the PEO weight ratio increasing from 2.5 to 15.0% (vs. liquid electrolyte), rheological behavior measurement showed that the viscosity of the polymer gel electrolytes increased ca 465 times. However, it was observed by steady-state voltammetry and electrochemical impedance spectra (EIS) measurements that the diffusion coefficient of I3−/I− decreased constantly while the conductivity of the polymer gel electrolytes increased initially and then decreased. These two inconsistent behaviours showed that the mobility of Li+ was enhanced by PEO. EIS measurement revealed that the internal resistance of the DSCs were reduced since the enhanced mobility of Li+ was helpful for the transport of electrons within the TiO2 film through an ambipolar diffusion mechanism. When these polymer gel electrolytes were used to assemble DSCs, the conversion efficiency of DSCs increased continuously until it reached its maximum as the PEO weight ratio increased from 2.5 to 10.0%. By optimizing the dye adsorbing time and the thickness of the TiO2 film, a quasi-solid DSC based on a polymer gel electrolyte with a PEO weight ratio of 10.0% showed a considerable conversion efficiency, 6.12 and 10.11% under 100 and 30 mW cm−2 illumination, respectively. Finally, a stability test indicated that the more PEO was added into the polymer gel electrolytes, the better stability was obtained for the corresponding DSCs.
Co-reporter:Jiaoli Li, Liduo Wang, Xiangming Kong, Beibei Ma, Yantao Shi, Chun Zhan and Yong Qiu
Langmuir 2009 Volume 25(Issue 18) pp:11162-11167
Publication Date(Web):July 2, 2009
DOI:10.1021/la901488j
An efficient method using a polymer dispersion (PD) based on a copolymer of styrene and butyl acrylate to prepare TiO2 electrodes for dye-sensitized solar cells (DSCs) was introduced. The obtained TiO2 nanoporous film was investigated by scanning electron microscopy (SEM) and Brunauer−Emmett−Teller (BET) analysis. A porous structure with pore size distribution from tens of nanometers to several hundred nanometers or even micrometers was characterized. This offered the film a feature of high haze factor and porosity. When using the film as photoanode, a quasi-solid-state DSC was successfully fabricated. The device showed an improved per-weight-efficiency by a factor of 2.7, resulting from the reduced interfacial resistance and the enhanced light scattering effect revealed by electrochemical impedance spectroscopy and transmittance spectroscopy, respectively. The developed PD-based colloid is promising to be applied in production on a large scale as a result of its simple prescription and stability during storage. A proposal to further improve the porous film is also introduced at the end of the paper.
Co-reporter:Beibei Ma, Rui Gao, Liduo Wang, Fen Luo, Chun Zhan, Jiaoli Li, Yong Qiu
Journal of Photochemistry and Photobiology A: Chemistry 2009 Volume 202(Issue 1) pp:33-38
Publication Date(Web):5 February 2009
DOI:10.1016/j.jphotochem.2008.11.004
Only one sort of dye and a dye-modification material is used to form an alternating assembly structure in dye-sensitized solar cell. The alternating assembly can increase the adsorption of dye sensitizer, prohibit the aggregation of the dye, and retard the recombination reaction. These effects are investigated by ultraviolet–visible spectrum, Fourier transform infrared spectrum, transient photovoltages, current density–voltage characteristics and dark current measurements. The photon–electron conversion efficiency of the cell with alternating assembly structure rise by 16%, from 3.86% to 4.49% under AM 1.5 irradiation. And the stability of the cell is also improved.
Co-reporter:G.T. Lei, L.D. Wang, L. Duan, J.H. Wang, Y. Qiu
Synthetic Metals 2006 Volume 156(5–6) pp:495
Publication Date(Web):1 March 2006
DOI:10.1016/j.synthmet.2006.01.002
Co-reporter:Bin Li, Liduo Wang, Bonan Kang, Peng Wang, Yong Qiu
Journal of Photochemistry and Photobiology A: Chemistry 2005 Volume 172(Issue 2) pp:135-139
Publication Date(Web):31 May 2005
DOI:10.1016/j.jphotochem.2004.12.001
The performance of solid-state dye-sensitized solar cells using a conjugated polymer, poly(2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylenevinylene) (MEHPPV), was greatly improved by iodine doping in the hole transporting layer. The surface photovoltage spectroscopy (SPS) and electric-field-induced surface photovoltage spectroscopy (EFISPS) study on the undoped and iodine doped MEHPPV films were performed and indicated that iodine doping turned the n-type conduction of MEHPPV to p-type conduction, which was accompanied by an improvement of photocurrent from 27 μA/cm2 to 148 μA/cm2.
Co-reporter:Xingyao Liang, Wenzhe Li, Jiangwei Li, Guangda Niu and Liduo Wang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 43) pp:NaN16919-16919
Publication Date(Web):2016/09/26
DOI:10.1039/C6TA06735B
Interfacial engineering is an important method to achieve compact and smooth high-quality perovskite films in a one-step method. In this work, we first demonstrate that lead monoxide (PbO) as an interfacial modification material could convert to perovskite crystal seeds and induce the growth of the CH3NH3PbI3−xClx absorber layer. The introduction of the perovskite crystal seeds resulted in a dramatically enhanced coverage and a large grain size of the perovskite films. The PL lifetime measurements verified reduced trap states of the perovskite thin films and enhanced charge transfer at the TiO2/perovskite interface. With a high quality perovskite thin film, the planar perovskite solar cell showed a remarkably improved power conversion efficiency (PCE) of 17.03%. Moreover, the device with PbO as an interfacial layer exhibited superior UV-stability, maintaining 60% of the initial PCE under intensive UV irradiation for 180 min while the control device was almost exhausted.
Co-reporter:Yifeng Zhu, Yantao Shi, Liduo Wang, Rui Gao, Beibei Ma, Yi Geng and Yong Qiu
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 45) pp:NaN15006-15006
Publication Date(Web):2010/10/18
DOI:10.1039/C004372A
The interface modification effect within quasi-solid dye-sensitized solar cells and the photovoltaic performance were investigated after the introduction of Mg(OOCCH3)2 as an additive into a polymer gel electrolyte. Electrochemical impedance spectroscopy showed that the addition of Mg(OOCCH3)2 into the polymer gel electrolyte can efficiently retard charge recombination at the TiO2/electrolyte interface. Mg(OOCCH3)2 in the electrolyte can also contribute to the enhancement of the incident photon-to-electron conversion efficiency by modifying the dye molecules. This results in an improvement in the photovoltage and photocurrent due to a barrier layer at the TiO2/electrolyte interface and the promotion of charge injection at the dye/TiO2 interface, respectively. Photovoltaic measurements reveal that a conversion efficiency enhancement from 4.05% to 4.96% under 100 mW cm−2 is obtained after the amount of Mg(OOCCH3)2 added was optimized.
Co-reporter:Rui Gao, Yixiu Cui, Xiaojiang Liu, Liduo Wang and Guozhong Cao
Journal of Materials Chemistry A 2014 - vol. 2(Issue 13) pp:NaN4770-4770
Publication Date(Web):2014/01/14
DOI:10.1039/C3TA15276F
A novel ZnO nanorod/nanoparticle (NR/NP) hierarchical structure on a zinc foil has been fabricated through a chemical bath deposition method. When used as a flexible photoanode for DSSCs, such a structure demonstrated enhanced dye-loading and electron lifetime as compared to the NR structure. It also retarded the charge recombination while maintaining the electron diffusion length of the NR structure. As a result, the power conversion efficiency of the DSSCs based on the NR/NP structure increased from 1.35% to 3.63% with a 169% enhancement as compared to that based on ZnO NRs.
Co-reporter:Wenzhe Li, Haopeng Dong, Xudong Guo, Nan Li, Jiangwei Li, Guangda Niu and Liduo Wang
Journal of Materials Chemistry A 2014 - vol. 2(Issue 47) pp:NaN20111-20111
Publication Date(Web):2014/10/16
DOI:10.1039/C4TA05196C
The interface between perovskite and the hole transport layer (HTL) is sensitive to photoelectric conversion properties. However, this study shows that the interface wettability of the HTL solution on a perovskite surface could be improved. To address this problem, graphene oxide (GO) with amphiphilic function was used to form a buffer layer between the perovskite and the HTL. After the GO modification, the contact angles of the HTL solution on the perovskite film decreased to zero degrees. X-ray photoelectron spectroscopy revealed that the GO interacts with the perovskite by forming Pb–O bonds, and Raman spectroscopy analysis revealed that the two-dimensional carbon–carbon bonds absorbed the hole transport material, 2,29,7,79-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,99-spirobifluorene (Spiro-MeOTAD) via π–π interactions. The GO layer improved the contact between the perovskite and HTL, resulting in an enhancement of the short circuit current (JSC). Moreover, using GO as an insulating buffer layer can retard charge recombination in solar cells, as revealed by EIS measured in dark conditions, leading to a significant increase in the open-circuit voltage (VOC) and the fill factor (FF). Consequently, the corresponding average efficiency greatly increased by 45.5%, from 10.0% to 14.5%. Therefore, application of GO as a dual-functional buffer layer on the perovskite layer is a useful strategy for preparing highly efficient hybrid perovskite solar cells.
Co-reporter:Wenzhe Li, Jiangwei Li, Jiaoli Li, Jiandong Fan, Yaohua Mai and Liduo Wang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 43) pp:NaN17110-17110
Publication Date(Web):2016/10/10
DOI:10.1039/C6TA08332C
The poor stability of hybrid organic–inorganic perovskite is one of crucial problems limiting the practical application of the perovskite solar cells (PSCs). All-inorganic lead-free perovskite materials, with Cs replacing the organic cations and Sn replacing Pb, have shown great potential in achieving high thermal stability. However, tin-based perovskites have inevitably suffered from severe bulk recombination, attributed to Sn vacancies. In this work, we obtain CsSnIBr2 thin films with low Sn vacancy assisted by the addition of hypophosphorous acid (HPA). The HPA additive here as complexant is demonstrated to be capable of speeding up the nucleation process while inhibiting the formation of Sn4+ during the formation process of CsSnIBr2 thin films. With a mesoscopic architecture, the CsSnIBr2 PSCs exhibit efficiency-loss free in 77 days and remarkably stable power output within 9 hours at high temperatures up to 473 K.
Co-reporter:Yantao Shi, Chun Zhan, Liduo Wang, Beibei Ma, Rui Gao, Yifeng Zhu and Yong Qiu
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 21) pp:NaN4235-4235
Publication Date(Web):2009/03/23
DOI:10.1039/B901003C
The electrically conductive function of high-molecular weight poly(ethylene oxide) (PEO) (Mw = 2 × 106 g mol−1) was investigated when it was used to gelate liquid electrolyte to fabricate a series of polymer gel electrolytes for dye-sensitized solar cells (DSCs). With the PEO weight ratio increasing from 2.5 to 15.0% (vs. liquid electrolyte), rheological behavior measurement showed that the viscosity of the polymer gel electrolytes increased ca 465 times. However, it was observed by steady-state voltammetry and electrochemical impedance spectra (EIS) measurements that the diffusion coefficient of I3−/I− decreased constantly while the conductivity of the polymer gel electrolytes increased initially and then decreased. These two inconsistent behaviours showed that the mobility of Li+ was enhanced by PEO. EIS measurement revealed that the internal resistance of the DSCs were reduced since the enhanced mobility of Li+ was helpful for the transport of electrons within the TiO2 film through an ambipolar diffusion mechanism. When these polymer gel electrolytes were used to assemble DSCs, the conversion efficiency of DSCs increased continuously until it reached its maximum as the PEO weight ratio increased from 2.5 to 10.0%. By optimizing the dye adsorbing time and the thickness of the TiO2 film, a quasi-solid DSC based on a polymer gel electrolyte with a PEO weight ratio of 10.0% showed a considerable conversion efficiency, 6.12 and 10.11% under 100 and 30 mW cm−2 illumination, respectively. Finally, a stability test indicated that the more PEO was added into the polymer gel electrolytes, the better stability was obtained for the corresponding DSCs.
Co-reporter:Wenzhe Li, Haopeng Dong, Liduo Wang, Nan Li, Xudong Guo, Jiangwei Li and Yong Qiu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 33) pp:NaN13592-13592
Publication Date(Web):2014/06/20
DOI:10.1039/C4TA01550A
4-tert-Butylpyridine (TBP) has been an important component in hole transport layer for hybrid perovskite solar cells. However, our study shows that TBP can corrode the perovskite absorption layer (CH3NH3PbI3) and interfere with the stability of the solar cells. To address this problem, montmorillonite (MMT) was used to form a buffer layer on top of the hole transport layer. XRD results revealed that TBP was intercalated in the MMT structure and UV-vis spectroscopy analysis revealed that this structure could prevent the corrosion of the CH3NH3PbI3 layer. Moreover, the MMT buffer layer could limit charge recombination in the solar cells. A delayed corrosion led to an increased current density owing to enhanced absorption, while a reduced charge recombination led to an increased fill factor and open voltage circuit values. Consequently, the corresponding efficiency largely increased from 9.0% to 11.9%, with an improvement of 32.2%. Therefore, the application of MMT as a bifunctional buffer coating layer on the hole transport layer is a useful strategy for preparing highly efficient hybrid perovskite solar cells with anti-corrosion and delayed charge recombination properties.
Co-reporter:Yantao Shi, Haopeng Dong, Liduo Wang, Chun Zhan, Rui Gao and Yong Qiu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 9) pp:NaN3188-3188
Publication Date(Web):2011/01/24
DOI:10.1039/C0JM03742G
In this paper, by altering reactants concentration, ZnO spindles with different sizes were controllably prepared through a fast precipitation process in aqueous solution. Some important characteristics such as specific area, macropore structure, light scattering and electron transport properties of the photoanodes were systematically investigated. The results showed that photoanodes composed of small-sized ZnO spindles had a larger specific area for dye-loading, while the large-sized ZnO spindles had more efficient light scattering and electron transport properties. Furthermore, to combine the advantages of different sized ZnO particles, composite photoanodes were fabricated by mixing together ZnO spindles of different sizes. Compared with the dye sensitized solar cells (DSCs) using photoanodes with single-sized ZnO spindles, the devices based on composite photoanodes showed a higher short-circuit photocurrent density without obvious decrease in open-circuit voltage and fill factor. As a result, photovoltaic performances of the DSCs were improved remarkably.
Co-reporter:Haopeng Dong, Liduo Wang, Rui Gao, Beibei Ma and Yong Qiu
Journal of Materials Chemistry A 2011 - vol. 21(Issue 48) pp:NaN19394-19394
Publication Date(Web):2011/11/01
DOI:10.1039/C1JM14191K
ZnO
nanorod–nanoparticles (NR–NPs) hierarchical structure was prepared via a two-step hydrothermal process at 70 °C. In the hierarchical structure, ZnO nanorods prepared at step one served as the backbone for direct electron transport while ZnO nanoparticles synthesized at step two offered large surface area for dye-loading. Both reaction temperature and reaction time at step two had a significant influence on the morphology of the product. At a higher temperature, microspheres appeared above the nanorod film instead of nanoparticles surrounding the nanorods. Prolonging the reaction time to 24 h, the NR–NPs structure would transform to nanorod–nanoplants. Intensity-modulated photocurrent spectroscopy results showed that the photoanode composed of the NR–NPs hierarchical structure had an electron diffusion coefficient (Dn) much higher than that of the nanoparticles. The dye desorption results showed that the dye adsorption amount for the NR–NPs structure was as much as 250% of that for the nanorods. Compared with dye-sensitized solar cells (DSCs) based on nanorods, the incident photon-to-electron conversion efficiency of the DSCs based on NR–NPs hierarchical structure improved remarkably. Under AM 1.5G illumination (100 mW cm−2), the power conversion efficiency of DSCs based on photoanodes composed of NR–NPs hierarchical structure exhibited a significant improvement (more than 120%) compared with that of ZnO nanorods.
Co-reporter:Rui Gao, Guangda Niu, Liduo Wang, Yi Geng, Beibei Ma, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 17) pp:NaN5978-5978
Publication Date(Web):2012/03/05
DOI:10.1039/C2CP24137D
In this paper, 8-hydroxyquinoline aluminium (Alq3) was used in interface modification of dye-sensitized solar cells (DSCs). Alq3 was the first discovered interface modification material with combined effects of retarding charge recombination and Förster resonant energy transfer (FRET). Results of dark current curve and AC impedance showed that Alq3 could retard charge recombination in DSCs. I–V curves showed that conversion efficiency increased with Alq3 modification. Besides the interface modification effect, it was discovered that Alq3 also acted as energy relay dye with the FRET effect between itself and N3, which increased photoresponse and electron injection. The application of Alq3 with combined effects opened a new door to explore more novel multi-functional interface modification materials to improve the performance of DSCs.
Co-reporter:Guangda Niu, Nan Li, Liduo Wang, Wenzhe Li and Yong Qiu
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 34) pp:NaN18332-18332
Publication Date(Web):2014/07/11
DOI:10.1039/C4CP02520B
Combined post-modification strategy of iodide ligands and wide band gap ZnS layer were employed in quantum dot sensitized solar cells. J–V curves show that the combined post-modification could improve the photoconversion efficiency compared to the single post-modification of ZnS because of the more effective passivation. CdS-sensitized and CdS/CdSe-co-sensitized solar cells both reveal that the assembly structure of QDs/I−/ZnS is more beneficial for the efficiency of solar cells than that of QDs/ZnS/I−. EIS results show that the former structure exhibit higher interface resistance and could suppress electron recombination more powerfully. XPS results reveal that the iodide ligands have different binding energy, which indicates a different coordination state of the iodide atom in these two structures. Finally, 3.28% efficiency and 18.16 mA cm−2 were achieved for CdS/CdSe QDSCs by applying this combined post-modification.
Co-reporter:Guangda Niu, Wenzhe Li, Fanqi Meng, Liduo Wang, Haopeng Dong and Yong Qiu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 3) pp:NaN710-710
Publication Date(Web):2013/11/04
DOI:10.1039/C3TA13606J
Degradation of perovskite has been a big problem in all-solid-state perovskite solar cells, although many researchers mainly focus on the high efficiency of these solar cells. This paper studies the stability of CH3NH3PbI3 films and finds that CH3NH3PbI3 is sensitive to moisture. The degradation reaction is proposed according to UV-Vis spectra and XRD results. In order to improve the degradation of CH3NH3PbI3, we introduce aluminum oxide as a post-modification material into all-solid-state perovskite solar cells for the first time. UV-Vis spectra show that Al2O3 modification could maintain the absorption of CH3NH3PbI3 after degradation. XRD results reveal that Al2O3 could protect perovskite from degradation. Moreover, the device post-modified by Al2O3 has shown more brilliant stability than that without modification when exposed to moisture. EIS results and dark current illustrate that the modification increased interface resistance in the dark, indicating the restrained electron recombination process.
Co-reporter:Nan Li, Haopeng Dong, Hua Dong, Jiaoli Li, Wenzhe Li, Guangda Niu, Xudong Guo, Zhaoxin Wu and Liduo Wang
Journal of Materials Chemistry A 2014 - vol. 2(Issue 36) pp:NaN14978-14978
Publication Date(Web):2014/07/14
DOI:10.1039/C4TA02921F
In this study, the crucial role of perovskites capping layers in the TiO2/CH3NH3PbI3 hybrid solar cells is investigated. The capping layers are realized by controlling the concentration of PbI2 solutions in the sequential deposition process. The morphologies of the active layers are studied by high-resolution scanning electron microscopy (HR-SEM). The amount of perovskites in capping layers increases with the concentration of PbI2 solution, and the coverage of perovskite capping layers on TiO2 films is better developed. Except for the correlation between photocurrents and coverages of perovskite proposed by Snaith, we revealed a more detailed relationship between the photovoltaic performances and perovskite capping layers. It is noteworthy that UV-vis absorption increased with perovskites in capping layers. Moreover, according to the diffuse reflection spectra, light scattering, which is beneficial for the conversion efficiency of photons to electrons by directly preventing most of the incident light from transmitting out, is also enhanced due to both the emergence of larger-size particles in the capping layers and the higher effective dielectric coefficient. All of the aforementioned aspects result in high photocurrents up to 20.6 mA cm−2. Efficiency as high as 10.3% is ultimately achieved by a simple control of PbI2 concentration in the sequential deposition process.
Co-reporter:H. P. Dong, Y. Li, S. F. Wang, W. Z. Li, N. Li, X. D. Guo and L. D. Wang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 18) pp:NaN10004-10004
Publication Date(Web):2015/03/27
DOI:10.1039/C5TA00407A
Interface engineering is an important and efficient way to further improve the conversion efficiency of perovskite solar cells. In this study, we report the modification of the electron transport layer (ETL) using a thin layer of PEO. Characterizations showed that PEO was uniformly coated on top of the original TiOx ETL, without resulting in an evident change of the surface morphology, hydrophilic ability or transparency. With the interface dipole formed at the interface, the work function of the ETL greatly decreased. Compared with devices with TiOx only, devices based on the modified ETL gave a nearly 15% enhancement to the overall conversion efficiency, with both Voc and Jsc improved. Further studies showed that the improved performance could mainly be attributed to the better retardation of back recombination and the enhanced electron collection efficiency by means of the PEO thin layer modification.
Co-reporter:Guangda Niu, Xudong Guo and Liduo Wang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 17) pp:NaN8980-8980
Publication Date(Web):2014/12/03
DOI:10.1039/C4TA04994B
In recent years, the record efficiency of perovskite solar cells (PSCs) has been updated from 9.7% to 20.1%. However, there has been very little study of the issue of stability, which restricts the outdoor application of PSCs. The issues of the degradation of perovskite and the stability of PSC devices should be urgently addressed to achieve good reproducibility and long lifetimes for PSCs with high conversion efficiency. Without studies on stability, exciting achievements cannot be transferred from the laboratory to industry and outdoor applications. In order to improve their stability, a basic understanding of the degradation process of PSCs in different conditions should be acquired via thorough study. This review summarizes recent studies of the relationship of the chemical stability of PSCs with their environment (oxygen and moisture, UV light, solution process, temperature) and corresponding possible solutions.
Co-reporter:Jiangwei Li, Wenzhe Li, Haopeng Dong, Nan Li, Xudong Guo and Liduo Wang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 16) pp:NaN8889-8889
Publication Date(Web):2015/03/16
DOI:10.1039/C4TA05762G
Lithium salts have been important additives to the hole-transport materials of solid-state hybrid perovskite solar cells to achieve higher hole mobility. However, the observed intercalation of Li+ into TiO2 was demonstrated to decrease the open-circuit voltage (VOC) of the cells. In this work, spinel lithium titanate Li4Ti5O12 (LTO) was used to alleviate this issue by consuming Li+ prior to the contact of Li+ with TiO2 at the interface between sensitized TiO2 and the hole-transport layer through the chemical insertion of Li+ into LTO. Raman and X-ray photoelectron spectroscopy results confirmed the insertion of Li+ into LTO. A Li+ insertion peak in cyclic voltammetry and an increased density of states of TiO2 revealed the role of LTO as a Li+ separator to protect the TiO2 photoanode, providing the mechanism of VOC increase for LTO modification. Electrochemical impedance spectroscopy revealed that LTO modification markedly reduced carrier recombination, improving the fill factor of the devices. Overall, the conversion efficiencies of the devices were significantly increased with a maximum efficiency of 15.1% by addition of LTO. The strategy of using LTO as a multifunctional modifier broadens the scope of interface engineering in solar cells.
Co-reporter:Yi Geng, Yantao Shi, Liduo Wang, Beibei Ma, Rui Gao, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 6) pp:NaN2421-2421
Publication Date(Web):2010/11/25
DOI:10.1039/C0CP01866J
Montmorillonite (MMT) added to electrolytes has been reported in the literature to facilitate the transport of I−/I3−, and improve the ionic conductivity and consequent photocurrent of dye-sensitized solar cells (DSCs). This paper firstly observes, investigates and reports that MMT addition to a poly(ethylene oxide) (PEO)-based gel electrolyte not only improves the ionic conductivity of the gel electrolyte, but also increases the photovoltage and decreases the dark current. From the results of electrochemical impedance spectroscopy (EIS) and transient photovoltage spectra, we evidence that MMT in the polymer gel electrolyte can efficiently retard the charge recombination that occurs at the TiO2/dye/electrolyte interfaces.
Co-reporter:Guangda Niu, Liduo Wang, Rui Gao, Wenzhe Li, Xudong Guo, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 45) pp:NaN19600-19600
Publication Date(Web):2013/07/31
DOI:10.1039/C3CP52678J
Halogen ions (I−, Br−, Cl−) were added into a colloidal solution of CdSe and PbS quantum dots (QDs) to form QDs capped with these inorganic ligands. Halogen ions attached to QDs through electrostatic interactions and the varying coordination strength between the inorganic ligands and QDs led to different degrees of redispersion and stabilization in polar solvents. Moreover, we successfully conducted electrophoretic deposition (EPD) of QDs capped with inorganic ligands. Negatively charged QDs were adsorbed onto a positively charged TiO2 anode. The assembled QDs films were used in photovoltaic devices and offered better efficiency than QDs capped with organic ligands. This work demonstrates that halogen ions are indeed promising ligands to improve the stability of QDs with inorganic ligands and the EPD method shows prospects in assembling QDs films for practical applications.
Co-reporter:Wenzhe Li, Jiaoli Li, Liduo Wang, Guangda Niu, Rui Gao and Yong Qiu
Journal of Materials Chemistry A 2013 - vol. 1(Issue 38) pp:NaN11740-11740
Publication Date(Web):2013/07/29
DOI:10.1039/C3TA12240A
The method of post-modification by aluminum oxide was successfully introduced into perovskite sensitized solar cells with a liquid electrolyte. Post-modification by Al2O3 could both protect the perovskite sensitizer from corrosion by electrolyte and effectively suppressed electron recombination. The UV-vis spectra revealed an enhanced absorption especially in the long wavelength range after modification. The XRD results showed a disappeared peak of PbI2, demonstrating that the modification could effectively protect the perovskite from dissolution in the electrolyte. Stability test showed that the remaining JSC improved from 10% to 50% at a given period of time. The EIS results and dark current curves illustrated that this modification increased the interface resistance in dark, confirming that the electron recombination process was effectively restrained. Finally, the corresponding efficiency was largely increased from 3.56 to 6.00% by 68%. The strategy using aluminium oxide to post-modify a perovskite sensitized solar cell was therefore proved to be a useful tool for the optimization of perovskite sensitized solar cells.
Co-reporter:Nan Li, Haoyuan Li, Yu Li, Shufeng Wang and Liduo Wang
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 37) pp:NaN24097-24097
Publication Date(Web):2015/08/20
DOI:10.1039/C5CP03803K
In meso-superstructured solar cells (MSSCs), the state-of-the-art perovskite acts as both the light harvester and electron transporter due to its ambipolar properties. The inefficient pore filling and infiltration of perovskite directly affect the continuous distribution of perovskite in mesoporous Al2O3, resulting in discontinuous carrier transport in the mesoporous structure and insufficient electron injection to the compact TiO2 layer. Herein, we introduce a simple pre-spin-coating process to improve the infiltration and pore filling of perovskite, which results in higher light absorption and enhanced electron injection, as seen in UV-vis spectra and photoluminescence (PL) spectra, respectively. We first apply time of flight (TOF) experiments to characterize charge transport in MSSCs, and the results reveal that more continuous charge transport pathways are formed with the pre-spin-coating process. This effective method, with ease of processing, demonstrates obviously improved photocurrents, reaching an efficiency as high as 14%, and promotes the application of lead halide perovskite materials in the photovoltaics field.
Co-reporter:Rui Gao, Liduo Wang, Yi Geng, Beibei Ma, Yifeng Zhu, Haopeng Dong and Yong Qiu
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 22) pp:NaN10640-10640
Publication Date(Web):2011/05/05
DOI:10.1039/C0CP02820G
In this paper, the interface modification effects of 4-tertbutylpyridine (TBP), especially the interaction with dye molecules, were discussed. The results of FTIR showed that TBP interacted with dye molecules, in addition to its interaction with the TiO2 film. Reaction between N3 and TBP by the interaction force of the H atom in the –COOH group of N3 and the N atom of TBP could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. Furthermore, the results of cyclic voltammograms and UV-vis absorption edge revealed the interaction between TBP and dye molecules could cause the energy level of the dye molecules to change, influencing the electron injection efficiency in DSCs. The IPCE results indicated that with TBP modification, the injection efficiency decreased, but the electron collection efficiency was enhanced.
Co-reporter:Beibei Ma, Liduo Wang, Haopeng Dong, Rui Gao, Yi Geng, Yifeng Zhu and Yong Qiu
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 7) pp:NaN2658-2658
Publication Date(Web):2010/12/16
DOI:10.1039/C0CP02415E
PbS QDs have been synthesized by an in situ photocatalysis method using the photocatalytic activity of nanocrystalline TiO2 films. Both the photovoltaic response and size of the synthesized PbS QDs were analyzed. Compared with the conventional synthesis route, this method is simpler and produces less waste.
Co-reporter:Guangda Niu;Rui Gao;Beibei Ma;Haopeng Dong;Yong Qiu
Journal of Materials Chemistry A 2012 - vol. 22(Issue 33) pp:
Publication Date(Web):2012/07/31
DOI:10.1039/C2JM32459H
In this paper, inorganic iodide ligands were used in PbS quantum dot sensitized solar cells (QDSCs) with iodide/triiodide electrolytes. Inorganic ligands are employed to replace organic ligands in QDSCs for the first time. They combined effects of passivating surface states and decreasing the interface resistance between QDs and sensitized TiO2, QDs and electrolyte. Then the corrosion of PbS QDs by triiodide in iodide/triiodide electrolytes was suppressed and electron injection and hole transfer was much easier. Stability test verified iodide ligands could prevent PbS from corrosion of iodide/triiodide electrolytes. Electrochemical impedance spectroscopy (EIS) showed that iodide ligands effectively decreased the interface resistance and improved the electron transfer. Finally, the performance with iodide ligands was significantly improved and achieved 3.7 times that of the untreated cells in efficiency.
Co-reporter:Wenzhe Li, Jiangwei Li, Guangda Niu and Liduo Wang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 30) pp:NaN11695-11695
Publication Date(Web):2015/12/16
DOI:10.1039/C5TA09165A
The interface modification of perovskite thin films has shown great potential to boost the performance of perovskite solar cells during the last few years. Here we demonstrate that cesium chloride (CsCl) as crystal seeds can markedly enhance the coverage of the CH3NH3PbI3−xClx absorber layer on TiO2 in planar heterojunction solar cells, thus boosting the power conversion efficiency (PCE) to 16.8%, with a fill factor (FF) of 0.79. Also, the introduction of CsCl significantly improved the stability of CH3NH3PbI3−xClx under ultra violet (UV) irradiation, which has been verified by XRD, XPS and SEM measurements. The CsCl-treated devices maintained 70% of the original PCE after a prolonged intensive UV irradiation of 200 min while the untreated devices being almost exhausted. Furthermore, we proposed the mechanism concerning CsCl as the modification layer to improve the UV-induced stability issue of perovskite solar cells.
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![BIS(9,9'-SPIROBI[FLUORENE]-2-YL)METHANONE](http://img.cochemist.com/ccimg/782600/782504-07-8_b.png)
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