Efficient planar heterojunction perovskite solar cells (PHJ–PSCs) with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al were fabricated using air-induced high-quality CH3NH3PbI3 perovskite thin films, in which the air-inducing process was controlled with a humidity of ∼40%. The air exposure of CH3NH3PbI3 thin films could dramatically improve their properties with large grains and smooth surface, as well as uniform morphology, resulting in an impressive enhancement in carrier lifetime. The ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy results proved that the CH3NH3PbI3 film was n-doped by the absorption of H2O on the surface but was very stable without obvious degradation for 10 days’ exposure in air. The power conversion efficiency (PCE) of PHJ–PSCs with an air exposure process showed a significant increase up to 16.21% as compared to reference PHJ–PSCs with a PCE of 12.02%. The research work demonstrated that an air-exposure process with a suitable humidity could produce high-quality perovskite thin film for efficient PHJ–PSCs, which may pave a boulevard for fabricating high-efficiency PHJ–PSCs in atmospheric environment.

•Large-scale, R2R micro-gravure printing was developed to process ZnO as the electron transport layer (ETL).•The R2R printed ZnO ETL was used to fabricate inverted organic solar cells (OSCs) on flexible substrate.•The inverted OSCs showed comparable performance parameters for using R2R printed and spin-coated ZnO ETLs.•The commercial large-scale, R2R micro-gravure printing process could be potentially used to produce efficient OSCs.Large-scale, roll-to-roll (R2R) micro-gravure printing process was developed to deposit the electron transport layer (ETL) using low-temperature, solution-processable zinc oxide (ZnO) nanoparticle ink on flexible substrate for fabricating inverted organic solar cells (OSCs). The properties of micro-gravure R2R printed ZnO thin film was optimized via using web tension, substrate pre-treatment and printing speed, leading to high-quality and thickness controllable ZnO thin films. The inverted OSCs using R2R micro-gravure printed ZnO thin film as the ETL showed performance parameters comparable to those of spin-coated ZnO thin film ETL on the flexible substrate in both P3HT:PCBM and PTB7-Th:PC71BM based devices. The research demonstrated that the potentially commercial large-scale, R2R micro-gravure printing process could be used to produce high-quality ZnO thin film with controllable thickness for efficient inverted OSCs, which would accelerate the development of fully R2R micro-gravure printing OSCs and their commercialization.Download high-res image (314KB)Download full-size image

•The degradation behavior of perovskite solar cells (PSCs) was studied in both N2-filled glovebox and in air.•The PSCs stored in glovebox without encapsulation showed good stability.•The PSCs stored in air with humidity of 45% degraded dramatically just after 1 h exposure.•Perovskite film stored in air with humidity of 45% didn’t show obvious degradation.•The degradation of PSCs mainly resulted from the interface issues rather than perovskite film itself.The stability and degradation process of low-temperature, solution-processed planar heterojunction perovskite solar cells (PHJ-PSCs) with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al were studied in both nitrogen-filled glovebox and ambient environment (humidity ∼45%). The results suggested that PHJ-PSCs stored in glovebox without encapsulation showed good stability, and the power conversion efficiency (PCE) could be kept over 70% of original value even after 30 days. As compared, PHJ-PSCs stored in ambient environment without encapsulation showed an obvious degradation, and the PCE was about 35% of original value just after 1 h exposure in air. However, PHJ-PSCs fabricated with CH3NH3PbI3 thin films stored in ambient environment for the different times didn’t show obvious degradation and have the similar performance parameters, suggesting that the degradation of PHJ-PSCs mainly resulted from the interface issues rather than the attenuation of perovskite thin film itself. Furthermore, electrochemical impedance spectroscopy (EIS) characterization indicated that the degradation of photovoltaic performance parameters was prevailingly attributed to the interface degradation. The research provides good understanding to the stability and degradation process of low-temperature, solution-processed PHJ-PSCs, which would facilitate the stability improvement of PHJ-PSCs.

•High-quality CH3NH3PbI3 perovskite film is prepared via doctor blading in ambient condition.•The doctor-bladed CH3NH3PbI3 perovskite film is dependent on the in-situ substrate temperature.•The doctor-bladed, large-area CH3NH3PbI3 film has large grain size, good reliability and reproducibility.•The CH3NH3PbI3 photodetector exhibit a responsivity as high as 8.95 AW-1 and a fast response of about 7.0 ms.Organic-inorganic hybrid halide perovskites have attracted much research interest in optoelectronic field due to their excellent photoelectric properties. Herein, we report large-area and high-performance perovskite CH3NH3PbI3 photodetectors fabricated via in-situ thermal-treatment doctor blading technique in ambient condition (humidity ∼45%). As compared with spin-coating deposition technique, the doctor-bladed CH3NH3PbI3 films have larger grain size, as well as good reliability and reproducibility in large area. The doctor-bladed CH3NH3PbI3 photodetectors exhibited high detectivity (D*) of 2.9 × 1012 Jones and high responsivity (R) of 8.95 A/W, as well as the fast response time of less than 7.7 ms. The results indicate that doctor-bladed CH3NH3PbI3 film is a very promising candidate for fabricating large-scale and high-performance optoelectronic devices.Download high-res image (214KB)Download full-size image

High-performance organic heterojunction phototransistors are fabricated using highly ordered copper phthalocyanine (CuPc) and para-sexiphenyl (p-6P) thin films. The p-6P thin film plays an important role on the performance of CuPc/p-6P heterojunction phototransistors. It acts as a molecular template layer to induce the growth of highly ordered CuPc thin film, which dramatically improves the charge transport and decreases the grain boundaries. On the other hand, the p-6P thin film can form an effective heterojunction with CuPc thin film, which is greatly helpful to enhance the light absorption and photogenerated carriers. Under 365 nm ultraviolet light irradiation, the ratio of photocurrent and dark current and photoresponsivity of CuPc/p-6P heterojunction phototransistors reaches to about 2.2 × 104 and 4.3 × 102 A W−1, respectively, which are much larger than that of CuPc phototransistors of about 2.7 × 102 and 7.3 A W−1, respectively. A detailed study carried out with current sensing atomic force microscopy proves that the photocurrent is predominately produced inside the highly ordered CuPc/p-6P heterojunction grains, while the photocurrent produced at the boundaries between grains can be neglected. The research provides a good method for fabricating high-performance organic phototransistors using a combination of molecular template growth and organic heterojunction.

•High-purity black α-phase formamidinium lead iodide (FAPbI3) perovskite film was prepared via doctor blading in air.•The α-phase FAPbI3 perovskite has a large domain size over 200 μm with (00l) preferential orientation.•The FAPbI3 photodetectors were fabricated via doctor blading and exhibited a responsivity as high as 11.46 AW−1.•The FAPbI3 photodetectors showed a ratio of photocurrent/dark current up to 105 and a response speed as fast as 5.4 ms.High-purity black α-phase formamidinium lead iodide (FAPbI3, FA is NH2CHNH+) perovskite polycrystalline film was prepared using low-cost, high-output doctor-blading deposition technique in ambient condition without further annealing process and any additives. The resulting α-phase FAPbI3 perovskite has a large domain size over 200 μm with (00l) preferential crystallographic orientation. The photodetectors with an extremely simple structure were fabricated via doctor-blading, resulting in a responsivity as high as 11.46 AW−1, a ratio of photocurrent/dark current (Ilight/Idark) as large as 105 and a response speed as fast as 5.4 ms. The results suggest that low-cost doctor-blading technique in ambient condition potentially pave a way to eliminate the yellow δ-phase FAPbI3 and get a high-quality black α-FAPbI3 perovskite film, as well as fabricate efficient FAPbI3 perovskite optoelectronic devices.Download high-res image (250KB)Download full-size image

Perovskite photodetectors are fabricated via structuring a perovskite/organic heterojunction with CH3NH3PbI3 and a high-mobility and stable organic semiconductor dioctylbenzothieno [2,3-b] benzothiophene (C8BTBT), which possess broad range photoresponse from ultraviolet to near-infrared, fast response, and excellent stability. The CH3NH3PbI3/C8BTBT heterojunction photodetectors exhibit an excellent ratio of photocurrent to dark current, Ilight/Idark, as high as 2.4 × 104, a high responsivity up to 24.8 AW−1, and a fast response of about 4.0 ms. Meanwhile, the photodetectors can maintain 90% performance even exposed in ambient condition without encapsulation for 20 d. In addition, the detailed mechanism is disclosed based on ultraviolet photoemission spectroscopy, steady-state photoluminescence (PL) spectra, and PL lifetime experiments. The C8BTBT layer acts as an efficient hole-extraction layer to let the holes quickly transport to the electrodes due to its perfect filling in the gaps between perovskite grains, as well as its intrinsic high mobility and the energy-level match with the CH3NH3PbI3. The stable C8BTBT layer can well play as a waterproof layer as well to prevent the perovskite CH3NH3PbI3 from the degradation. The research provides an excellent method for fabricating high-performance and stable perovskite photodetectors using perovskite/organic heterojunction.

•Efficient perovskite solar cells (PSCs) were fabricated via in-situ thermal-annealing doctor blading in ambient condition.•The in-situ thermal-annealing temperature dramatically influence the formation process of CH3NH3PbI3 thin film.•The efficiency over 11% was achieved for PSCs with a simple structure of ITO/PEDOT:PSSS/CH3NH3PbI3/PCBM/Ag.•The in-situ thermal-annealing doctor blading can match with large-scale, roll-to-roll process in ambient condition.The in-situ thermal-annealing doctor blading was developed to fabricate high-quality perovskite CH3NH3PbI3 thin film and efficient planar heterojunction perovskite solar cells (PHJ-PSCs) in ambient condition with humidity of ∼45%. The morphology of CH3NH3PbI3 thin film fabricated by in-situ thermal-annealing doctor blading varied from random nanowires to oriented domains as increasing the substrate temperature, and the domain size became larger and larger with increasing substrate temperature. The PHJ-PSCs with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Ag was fabricated based on in-situ thermal-annealing doctor-bladed CH3NH3PbI3 thin film in ambient condition, resulting in the power conversion efficiency up to 11.29% without obvious hysteresis under different scanning directions and speeds. The performance is comparable to that of PHJ-PSCs fabricated by spin-coating deposition in glovebox with the same structure. The research results suggested that efficient PHJ-PSCs could be fabricated by large-scale in-situ thermal-annealing doctor blading in ambient condition, which is matchable with large-scale, roll-to-roll process and shows potential application in industrial production.Download high-res image (186KB)Download full-size image

Highly efficient planar heterojunction perovskite solar cells (PHJ–PSCs) with a structure of ITO/PEDOT:PSS/CH3NH3PbI3–xClx/PCBM/C60/Ag was fabricated, in which the compact and pinhole-free CH3NH3PbI3–xClx perovskite thin film was obtained using a mixture of precursors containing lead iodide (PbI2), lead chloride (PbCl2), and methylammonium iodide (CH3NH3I) at an optimized ratio of 1:1:4. The morphology and formation process of CH3NH3PbI3–xClx thin film was closely related to the annealing temperature and time, which would result in the controllable performance for the PHJ–PSC devices. The morphology, crystallization process, and element analysis suggested that the chlorine gradually diffused and sublimated from the film surface while the iodine moved to the surface, together with the removal of the pinholes in the film. The PHJ–PSCs with the as-prepared CH3NH3PbI3–xClx thin film showed good performance and excellent repeatability. The power conversion efficiency (PCE) up to 14.03% was achieved without obvious hysteresis under different scanning conditions. The understanding of the iodine and chlorine element evolving process during the thermal treatment is beneficial to develop a more efficient scalable one-step solution processing method for fabricating large-area, highly efficient CH3NH3PbI3–xClx-based PSCs.

Organic–inorganic hybrid halide perovskite nanowires (PNWs) show great potential applications in electronic and optoelectronic devices such as solar cells, field-effect transistors and photodetectors. It is very meaningful to fabricate ordered, large-area PNW arrays and greatly accelerate their applications and commercialization in electronic and optoelectronic devices. Herein, highly oriented and ultra-long methylammonium lead iodide (CH3NH3PbI3) PNW array thin films were fabricated by large-scale roll-to-roll (R2R) micro-gravure printing and doctor blading in ambient environments (humility ∼45%, temperature ∼28 °C), which produced PNW lengths as long as 15 mm. Furthermore, photodetectors based on these PNWs were successfully fabricated on both silicon oxide (SiO2) and flexible polyethylene terephthalate (PET) substrates and showed moderate performance. This study provides low-cost, large-scale techniques to fabricate large-area PNW arrays with great potential applications in flexible electronic and optoelectronic devices.

•C8BTBT-based OFETs with a mobility of 1.20 cm2 V−1 s−1 were fabricated by organic molecular beam deposition.•C8BTBT-based OFETs with a mobility of 3.56 cm2 V−1 s−1 were fabricated by solution processing.•The deposition parameters show great influence on the morphology and structure of C8BTBT thin film.•The polystyrene additive dramatically improves the crystallinity of C8BTBT thin film and the interface property.•C8BTBT-based OFETs exhibits the potential applications in flexible and printed electronics.Organic field-effect transistors (OFETs) based on organic semiconductor material 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8BTBT) as the active layer were fabricated by using organic molecular beam deposition (OMBD) and solution-processed methods, in which the C8BTBT thin-film morphology could be well controlled. In OMBD method, C8BTBT thin-film morphology could be controlled by the thickness of organic semiconductor layer and the deposition rate, of which the high-quality C8BTBT thin film was obtained at a thickness of about 20 nm and at a deposition rate of 1.2 nm/min, resulting in an obvious mobility improvement from 2.8 × 10−3 cm2 V−1 s−1 to 1.20 cm2 V−1 s−1. While in the solution-processing, C8BTBT thin-film morphology and thickness are related to the spin-coating speed and the substrate position in spin coater, i.e., in-centre and off-centre position. The off-centre spin-coating with an optimized speed produced large-size domain C8BTBT thin film and accordingly resulted in a mobility of 1.47 cm2 V−1 s−1. Furthermore, an additive polystyrene (PS) was added into C8BTBT solution could further improve the thin-film morphology with more metal-stable phase as well as improve the interface contact with the substrate SiO2, resulting in the highest mobility up to 3.56 cm2 V−1 s−1. The research suggested that C8BTBT-based OFETs with the mobility over 1.20 cm2 V−1 s−1 could be fabricated by using both OMBD and solution-processed methods through the thin-film morphology and structure optimization, which shows the potential applications in high-performance flexible and printed electronics.

•Efficient perovskite solar cells (PSCs) were fabricated via two-step solution processes with intramolecular exchange.•The pre-deposited PbI2(DMSO) layer accelerated the formation of high-quality CH3NH3PbI3 thin film.•The efficiency over 14% was achieved for PSCs with a simple structure of ITO/PEDOT:PSSS/CH3NH3PbI3/PCBM/Al.•The fabrication process could match with large-scale, roll-to-roll printing or coating techniques.The high-quality CH3NH3PbI3 perovskite thin film with excellent coverage and uniformity was prepared using an intramolecular exchange technology via a low-temperature, two-step sequential deposition process. The PbI2(DMSO) complex was synthesized at room temperature without any additives and was deposited, then the CH3NH3I solution was deposited subsequently. The further controllable thermal annealing process resulted in the complete formation of flat and uniform CH3NH3PbI3 thin film with large-size grains and (110) preferred crystallographic orientation. The perovskite solar cells (PSCs) with a very simple inverted planar heterojunction structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al and without other buffer layers, e.g., C60, LiF, BCP, etc., were fabricated, resulting in a power conversion efficiency (PCE) as high as 14.26%. The results suggest that the low-temperature, two-step sequential deposition process with intramolecular exchange technology provides a good route to fabricate high-quality perovskite thin film and efficient PSCs, which would match with large-scale, high-output roll-to-roll (R2R) printing/coating techniques.

Organic solar cells (OSCs) continuously attract much attention due to their potentials as the low-cost and lightweight sources of renewable energy, and the power conversion efficiency (PCE) of the state-of-the-art OSCs has reached over 10.0%. Especially, there has been an unexpected breakthrough and rapid evolution of highly efficient organic-inorganic hybrid perovskite solar cells (PSCs), and the PCE has been improved to over 20%. The interface plays a very important role on the performance of both OSCs and PSCs, as well as their stability. It is imperative to control the interface properties and understand the mechanisms for obtaining highly efficient OSCs and PSCs. In this review, we will summarize our research progress on the interface modification of OSCs and PSCs using the electron transport layer and hole transport layer, as well as the molecular template layer.有机太阳能电池具有柔性、廉价、质轻等优势, 多年来一直受到研究人员的大量关注, 光电转换效率已经达到10%以上. 特别是最近几年, 基于有机-无机杂化的钙钛矿太阳能电池发展迅猛, 短短几年内, 光电转换效率突破了20%. 界面对有机和钙钛矿太阳能电池的光电转换效率和稳定性具有举足轻重的作用. 因此, 研究人员聚焦有机和钙钛矿太阳能电池的界面材料、界面修饰、界面工程等开展了深入研究, 并取得了诸多进展. 本文主要基于作者课题组多年来在有机和钙钛矿太阳能电池的界面研究所取得的初步进展进行了总结, 并对界面材料的发展方向进行了展望, 期望满足未来基于印刷技术制备高效率、大面积、柔性有机和钙钛矿太阳能电池的需要.

Highly efficient planar heterojunction (PHJ) perovskite solar cells (PSCs) with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al were fabricated by a low-temperature solution process. As employed silica-coated gold (Au@SiO2) nanorods at the interface between the hole transport layer PEDOT:PSS and the active layer CH3NH3PbI3, the average power conversion efficiency (PCE) showed over 40% enhancement, of which the average PCE was improved from 10.9% for PHJ-PSCs without Au@SiO2 to 15.6% for PHJ-PSCs with Au@SiO2, and the champion one up to 17.6% was achieved. Both experiment and simulation results proved that prominent efficiency enhancement comes from the localized surface plasmon resonance of Au@SiO2 nanorods which could improve the incident light trapping as well as improve the transport and collection of charge carrier, resulting in the enhancement in device parameters. The results suggest that metal nanorods, e.g., Au@SiO2, could be employed to fabricate high-efficiency and low-cost PHJ-PSCs.

•P3HT, PCBM, and P3HT:PCBM blend solutions have different stabilities, and influence the device performance differently.•These solutions are much more stable than P3HT, PCBM, and P3HT:PCBM in thin film form.•P3HT:PCBM blend solution can be stable over two months, much more stable than P3HT or PCBM solutions stored separately.•P3HT and PCBM could stabilize each other in their blend solution resulting from the formation of P3HT:PCBM dimers.•It provides a new understanding of the solution stability of active materials, and has great practical applications.The solution stability of the active materials poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61 butyric acid methyl ester (PCBM), and P3HT:PCBM blends were studied by a combination of organic photovoltaic (OPV) device performance, ultraviolet–visible (uv–vis) spectroscopy, and simulation calculations. OPV devices based on the structure ITO/PEDOT:PSS/Active layer (P3HT:PCBM)/Al showed that pure P3HT, pure PCBM, and P3HT:PCBM blend solutions could be stable for as long as one month when stored in either a glovebox or in air. Especially, P3HT:PCBM solution blends are much more stable than P3HT or PCBM solutions stored separately, in which the former could be stored stably over two months. The addition of PCBM to P3HT solution forms P3HT:PCBM dimers, avoiding the formation of charge transfer complexes. The calculation results showed that the electronic wave-function of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are isolated in P3HT:PCBM dimers. The research provides a new understanding on the stability of P3HT and P3HT:PCBM solutions, and has great practical application in the fabrication of large-area OPV modules by printing or coating techniques.

•Efficient and non-hysteresis planar heterojunction perovskite solar cells were fabricated.•High-quality CH3NH3PbI3 perovskite film was obtained by solvent engineering.•The device performance is strongly dependent on the morphology of perovskite film.•The PCE up to 13.49% was achieved for organic/perovskite planar heterojunction solar cells.Highly efficient and non-hysteresis organic/perovskite planar heterojunction solar cells was fabricated by low-temperature, solution-processed method with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al. The high-quality perovskite thin film was obtained using a solvent-induced-fast-crystallization deposition involving spin-coating the CH3NH3PbI3 solution followed by top-dropping chlorobenzene with an accurate control to induce the crystallization, which results in highly crystalline, pinhole-free, and smooth perovskite thin film. Furthermore, it was found that the molar ratio of CH3NH3I to PbI2 greatly influence the properties of CH3NH3PbI3 film and the device performance. The equimolar or excess PbI2 was facile to form a flat CH3NH3PbI3 film and produced relatively uniform perovskite crystals. Perovskite solar cells (PSCs) with high-quality CH3NH3PbI3 thin film showed good performance and excellent repeatability. The power conversion efficiency (PCE) up to 13.49% was achieved, which is one of the highest PCEs obtained for low-temperature, solution-processed planar perovskite solar cells based on the structure ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al. More importantly, PSCs fabricated using this method didn’t show obvious hysteresis under different scan direction and speed.

•Efficient electron-blocking layer (EBL)-free perovskite solar cells (PSCs) were fabricated.•The EBL-free PSCs were simply structured with ITO/CH3NH3PbI3/PCBM/Al.•The power conversion efficiency (PCE) of over 11% was achieved in EBL-free PSCs.•The open-circuit voltage (Voc) up to 1.06 V was obtained in EBL-free PSCs.Perovskite solar cells (PSCs) with a simple device structure are particularly attractive due to their low cost and convenient fabrication process. Herein, highly efficient, electron-blocking layer (EBL)-free planar heterojunction (PHJ) PSCs with a structure of ITO/CH3NH3PbI3/PCBM/Al were fabricated via low-temperature, solution-processed method. The power conversion efficiency (PCE) of over 11% was achieved in EBL-free PHJ-PSCs, which is closed to the value of PSC devices with the PEDOT:PSS as the EBL. It is impressed that the open-circuit voltage (Voc) up to 1.06 V, an average value of 1.0 V for 43 devices, was obtained in EBL-free PHJ-PSCs. The electrochemical impedance spectroscopy (EIS) results suggested that the high PCE and Voc are attributed to the relatively large recombination resistance and low contact resistance in EBL-free PHJ-PSCs. The solution-processed, EBL-free PHJ structure paves a boulevard for fabricating high-efficiency and low-cost PSCs.

•Solution-processed, annealing-free TiO2 NPs layer was fabricated and used in organic photovoltaics (OPVs).•The OPV performance was dramatically enhanced with inserting an annealing-free TiO2 NPs layer.•Solution-processed, annealing-free TiO2 NPs shows greatly potential applications in printable OPVs.A solution-processed, annealing-free TiO2 nanocrystalline particles (TiO2 NPs) as an interface modification layer was inserted in organic photovoltaics (OPVs), in which the widely used polymer poly (3-hexyl thiophene) (P3HT), a low band gap alkoxylphenyl substituted [1,2-b:4,5-b′] dithiophene-based polymer (PBDTPO-DTBO), and a soluble small molecule benzodithiophene derivative (TIBDT) were used as the donor material, respectively. The annealing-free TiO2 NPs could be easily spin-coated upon the surface of organic active layers, and showed comparable properties to thermal-annealed ones. The power conversion efficiencies (PCEs) of OPV devices could be enhanced dramatically with inserting an annealing-free TiO2 NPs layer. The PCEs of OPV devices based on P3HT:PC61BM, PBDTPO-DTBO:PC71BM and TIBDT:PC61BM bulk heterojunctions were improved by 28%, 15% and 27%, respectively, with an annealing-free TiO2 NPs layer, in which the highest PCE of 5.76% was achieved in PBDTPO-DTBO:PC71BM OPVs. The solution-processed, annealing-free TiO2 NPs thin films show great potential applications in the fabrication of large-area OPVs by printing or coating techniques on flexible polymer substrates. In particularly, it would promote to fabricate solution-processed, annealing-free OPV devices with suitable hole transport layer and organic/polymer active materials.

Conduction of electric charges is often done in polycrystalline materials. Unavoidably, the crystallite size, orientation, and domain boundaries (DBs) affect the transport of the charge carriers. It is particularly so for organic semiconductors known to be highly anisotropic and strongly dependent on DBs. Understanding those effects will have a strong impact on improving the performance of organic electronic and optoelectronic devices. Herein, we report our investigation on the crystal-domain orientation and boundary on the charge transport of operating device with copper phthalocyanine (CuPc) thin films grown on p-sexiphenyl (p-6P) by Kelvin probe force microscopy. In CuPc intradomains, the voltage drop increases as the angle increases between the domain orientation and the source-drain electric field. In DBs, the potential wells and steep voltage drops were observed. The increase of the DBs width and the angle between the orientations of neighboring domains results in the raise of voltage drop across the DBs, which restrict the charge transport in DBs simultaneously. The mobility of CuPc thin films increases with the domain size, resulting from the reduction of the mismatched orientation degree and the number of DBs.

•Organic small molecule photovoltaics were fabricated by interface modification.•An inserted molybdenum oxide layer largely enhances open-circuit voltage.•An inserted molecular template layer dramatically improves short-circuit current.•The power conversion efficiencies are almost doubled with interface modification.We report discrete heterojunction small molecular organic photovoltaics (OPVs) with enhanced performance by modifying the interface using molybdenum oxide (MoOx) and molecular template layer perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA). A large increase in open-circuit voltage was obtained in copper phthalocyanine/fullerene, i.e., CuPc/C60 and CuPc/PCBM, discrete planar heterojunction photovoltaics with an insertion of 5 nm MoOx hole transport layer at the interface between the anode electrode and the CuPc donor layer. It results from the band bending at the interface and the pinning of the highest occupied molecular orbital level of CuPc to the Fermi level of MoOx due to the defect states (oxygen vacancies) in MoOx thin films. Moreover, the short-circuit current showed an efficient improvement by inserting a 1 nm PTCDA layer at the interface between the MoOx layer and the CuPc layer. The PTCDA layer induces the growth of CuPc thin film with lying-down molecular arrangement, supporting the charge transports along the vertical direction. The power conversion efficiencies of CuPc/C60 and CuPc/PCBM discrete planar heterojunction photovoltaic devices were improved from about 0.80% to 1.50% with inserting both MoOx and PTCDA layers. The results suggest that the performance of organic discrete planar heterojunction photovoltaics could be optimized by interface modification with combining hole transport layer and molecular template layer, which are potentially suitable for other highly efficient OPVs, such as small molecular tandem OPVs.

•PBDFTDTBT is a benzo[1,2-b:4,5-b′]difuran-based donor–acceptor (D–A) conjugated polymer.•PBDFTDTBT is used to fabricate organic field-effect transistors (OFETs) with good performance.•PBDFTDTBT OFETs show a hole mobility of 0.05 cm2/Vs and an on/off ratio of 4.6 × 105.•OFETs have a photosensitivity (Ilight/Idark) of 1.2 × 105 under white light illumination.•PBDFTDTBT OFETs are very stable and have no obvious degeneration for 3 months in air.Organic field-effect transistors (OFETs) were fabricated through a solution process with a donor–acceptor (D–A) conjugated polymer poly{4,8-bis(2′-ethylhexylthiophene)benzo [1,2-b;3,4-b′]difuran-alt-5,5-(4′,7′-di-2-thienyl-5′,6′-dioctyloxy-2′,1′,3′-benzothiadiazole)} (PBDFTDTBT) as the active layer, which is a highly efficient D–A conjugated polymer as a donor in polymer solar cells with a power conversion efficiency (PCE) over 6.0%. The OFET devices showed a hole mobility of 0.05 cm2/Vs and an on/off ratio of 4.6 × 105. Those are one of the best performance parameters for OFETs based on D–A conjugated polymers including benzo[1,2-b:4,5-b′]dithiophene (BDT) or benzo[1,2-b:4,5-b′]difuran (BDF) unit. The photoresponse of OFETs was investigated by modulating light with various intensities. The devices produced a photosensitivity (Ilight/Idark) of 1.2 × 105 and a photoresponsivity of 360 mA W−1 under white light illumination. The drain current in saturation region increases gradually with increasing illumination intensity. The threshold voltage exhibited a positive shift from −15.6 V in darkness to 27.8 V under illumination, which can be attributed to the well-known photovoltaic effect resulting from the transport of photogenerated holes and trapping of photogenerated electrons near the source electrode in organic phototransistors. Meanwhile, the devices showed good stability and with no obvious degeneration for 3 months in air. The study suggests that D–A conjugated polymers including BDF unit can be potentially applied in OFETs and organic phototransistors in addition to highly efficient polymer solar cells.Graphical abstract

•A facile solution-based method was developed to synthesize TiO2 nanoparticles (NPs).•The PSCs with a TiO2 NPs buffer layer have excellent improvement in PCE and stability.•The conventional structure PSC with TiO2 NPs based on P3HT:PCBM shows a PCE of 4.24%.•The TiO2 NPs play as an efficient ETL and HBL as well as optical spacer layer in PSCs.•TiO2 NPs have potential applications in PSCs, especially for large-area printed PSCs.TiO2 sols synthesized with a facile solution-based method were used as a buffer layer between the active layer and the cathode Al in conventional structure polymer solar cells (PSCs). Using transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) and atomic force microscopy (AFM), the morphological and crystallographic properties of synthesized TiO2 nanoparticles (TiO2 NPs) as well as the buffer layer were studied in detail. It was observed that by increasing H2O in the process of peptization both the crystallinity and particle size of TiO2 NPs were enhanced, while the particles in sol showed a narrower size distribution conformed by dynamic light scattering. Inserting TiO2 NPs as a buffer layer in conventional structure PSCs, both the power conversion efficiency (PCE) and stability were improved dramatically. PSCs based on the structure of ITO/PEDOT:PSS/P3HT:PCBM/TiO2 NPs/Al showed the short-circuit current (Jsc) of 12.83 mA/cm2 and the PCE of 4.24%, which were improved by 31% and 37%, respectively comparing with the reference devices without a TiO2 buffer layer. The stability measurement showed that PSC devices with a TiO2 NPs buffer layer could retain 80% of the original PCEs after exposed in air for 200 h, much better than the devices without such a buffer layer. The effect can be attributed to the protection by the buffer layer against oxygen and H2O diffusion into the active layers. The observations indicate that TiO2 NPs synthesized by facile solution-based method have great potential applications in PSCs, especially for large-area printed PSCs.Graphical abstract

•Low-temperature pre-synthesized TiO2 nanoparticles (NPs) were applied in inverted PSCs.•The power conversion efficiency (PCE) increases under exposure in air at the first 24 h.•The inverted PSCs with TiO2 NPs as the ETL showed a PCE of 4.56% and good stability.•Mott-Schottky capacitance was successfully to analyze both regular and inverted PSCs.•TiO2 NPs showed great potentials to fabricate efficient, stable, and flexible inverted PSCs.The performance of both inverted and conventional polymer solar cells (PSCs) were examined with a low-temperature, solution-processed synthesized TiO2 nanoparticles (TiO2 NPs) as the electron extraction layer. The performance of inverted PSCs based on P3HT:PCBM bulk-heterojunction with a TiO2 NPs layer was dramatically improved and the highest power conversion efficiency (PCE) of 4.56% was achieved via 24 h exposure in air, which is one of the highest PCEs for P3HT:PCBM bulk-heterojunction PSCs using TiO2 as electron extraction layer. Meanwhile, the performance of inverted PSCs was superior to regular PSCs. Mott-Schottky capacitance analysis was carried out for both inverted and regular PSCs to obtain the built-in potential, the depletion width, as well as the doping level of the active layer, which all support the performance improvement of PSCs devices with inverted structure. In addition, inverted PSCs show excellent stability in air without encapsulation. The PCE can retain 87% of its original values after 400 h exposure in air, which is much better than that of regular PSCs. The results indicate that solution-processed TiO2 NPs shows great potential applications in the fabrication of highly efficient and stable inverted PSCs as well as large-area, flexible printed PSCs.Graphical abstract