TiO2 nanoparticle is employed as mesoporous scaffold under low temperature in methylammonium lead iodide (MAPbI3) perovskite layer for planar heterojunction solar cells (PH PSCs). It has been found that the high quality perovskite crystalline is obtained by adding TiO2 nanoparticles into perovskite layer. The incident photon to current conversion efficiency (IPCE) has been significantly improved due to the enhanced light scattering of TiO2 nanoparticles and efficient electron transport in perovskite layer. Specially, interconnected TiO2 nanoparticles improves the electron transport property, leading to reducing hysteresis and obtaining the much higher power conversion efficiency (PCE) (12.96%) with Voc = 0.99 V, Jsc = 22.9 mA/cm2 and FF = 0.562. This fabrication method is promising for flexible PH PSCs application and reducing the preparation cost.

•The SnO2-TiO2 composite layers are low-temperature-processed.•The composite layer for efficient perovskite solar cells was demonstrated.•The composite layer improves the band-alignment and interface-contact.•The composite layer facilitates charge extraction and reduces carrier recombination.•The solar cell based on SnO2-TiO2 layer acquires an efficiency of 14.8%,Inorganic metal oxide electron-transport layers have the potential to promise perovskite solar cells with improved stability and high efficiency, but generally require high temperature to enhance conductivity and reduce defect. Here, low-temperature solution-processed inorganic SnO2-TiO2 composite layer for efficient planar heterojunction perovskite solar cells is demonstrated. The SnO2-TiO2 composite layer brings better bandgap matching at the perovskite/FTO interface that facilitates charge extraction and reduces surface recombination. Cyclic voltammetry, steady-state photoluminescence spectroscopy and electrical impedance spectroscopy were conducted to reveal the energy band alignment and charge carrier dynamics. The SnO2-TiO2 composite films based solar cells acquire a high power conversion efficiency (PCE) of 14.8%, which is higher than PCEs of devices based on individual SnO2 layer and sintered TiO2 layer.Low-temperature solution-processed inorganic SnO2-TiO2 composite layer brings perfect band-gap matching and closes interface-contact between perovskite layer and FTO substrate, which contributes to facilitating charge extraction and reducing carrier recombination, leading to device efficiency as high as 15%.Download high-res image (159KB)Download full-size image

•Polymer assisted growth of high-quality perovskite films was demonstrated.•Polymer PMMA can retard nucleation and crystal growth of perovskite.•The interaction between the perovskite films and PMMA was addressed.•Planar-heterojunction solar cells with efficiencies of 15% were achieved.Long-chain insulating polymers dissolved in perovskite precursor solution can assemble the polymer scaffold acted as the function of TiO2 porous layer to improve the quality of the perovskite films. Here, perovskite films with high electronic quality were prepared by mediating nucleation and crystal growth. Polymer post treatment can induce Lewis acid-base reaction with PbCl2, which alleviates the reaction velocity between PbCl2 and CH3NH3I, and then retard perovskite crystallization. The interactions between the perovskite films and polymer with different concentration are addressed to interpret the function and evolution of the polymer long-chains during the annealing process. These solar cells exhibit efficiency more than 15% with small variation. Our work demonstrates the value of retarding nucleation and crystal growth by Lewis acid-base adducts for high-quality perovskite films.

•Ba doping enlarges the energy band gap of MAPb1-xBaxI3.•Voc and Jsc are enhanced in perovskite solar cells.•DFT calculation proves the experiment results.Elements substitution and doping in perovskite CH3NH3PbI3 exhibit versatile tunability of energy band structure and opto-electric properties. Ba2+ is chosen to substitute Pb2+ for its similar valence state and ionic radius with Pb2+. Ba2+ doping in perovskite (mol% <5) slightly enlarges the optic energy gap by conduction band minimum(CBM) upshifting to vacuum energy level, which is due to the smaller electronegativity of Ba than Pb. The enlarged band gap is also verified by density function theory calculations. In n-i-p structure perovskite solar cells (PSCs), because of the higher CBM of doped perovskite, the Fermi energy difference between n and p side is enlarged and the electron injection from the perovskite to TiO2 is improved. Thus, both the photovoltage and photocurrent are improved by small amount Ba2+ doping, resulting optimized 17.4% efficiency under AM1.5. This work reveals the relationship between the doping element property and the energy band structure of the perovskite, and highlights the doping method to improve the performance of PSCs.Download high-res image (138KB)Download full-size image

Morphology and crystallinity of perovskite layers are crucial for power conversion efficiency (PCE) of perovskite solar cells (PSCs). Here, we introduced amorphous polymer polyvinylpyrrolidone (PVP) with a CO functional group into a CH3NH3PbI3−xClx perovskite precursor to tune the morphology and crystallinity of perovskite layers during the film formation process. The spreading amorphous polymer chains and excellent hygroscopicity of PVP can help the perovskite precursor have better contact with the substrate, leading to better perovskite film coverage. More importantly, the electron pair existing in the oxygen atom of the CO bond in PVP has a strong attraction to Pb(II) ions, which can adjust the location of the nuclei and make the nuclei distribute uniformly in PVP chains, contributing to a uniform and compact perovskite layer. As a result, perovskite films with PVP present favourable morphology and improved crystallinity. The performance of a CH3NH3PbI3−xClx-based perovskite solar cell with optimized PVP content achieves a summit PCE of 16.57% with photovoltage VOC of 1057 mV, short circuit current density JSC of 21.38 mA cm−2, and fill factor FF of 74.52% under standard AM 1.5 solar light of 100 mW cm−2 intensities, which demonstrates a 23.9% increment compared with a PCE of 13.37% of the original device.

•A facile synthesis of perovskite microcrystals was demonstrated.•A tetragonal crystal structure was tested by XRD and FE-SEM.•Red shift and thermal stability were investigated by PL and DSC-TGA, respectively.•CH3NH3PbI3 microcrystal promises a candidate for optoelectronic applications.The organic–inorganic hybrid perovskite CH3NH3PbI3 is becoming an interesting material in the field of optoelectronic application. Most of the previous research focused on thin film and crystal growth of this material. Here we describe the rapid preparation of perovskite CH3NH3PbI3 microcrystals using a facile synthesis method at room temperature. By using ultrasound assisted solutions of PbI2 and CH3NH3I precursors in acid solvents, a single-phase perovskite was obtained. X-ray diffraction data reveal that the prepared CH3NH3PbI3 crystals possess a tetragonal structure. FE-SEM and TEM images show the morphology and grain size of CH3NH3PbI3 crystals. UV-VIS-NIR and PL measurements indicate that the perovskite crystals show a slight reduced bandgap, accompanying with red shift, compared with the perovskite polycrystalline films. DSC-TGA demonstrates that the perovskite microcrystals show the better thermal stability than that of the perovskite films, which suggests the wide potential application.

•We designed a new structure of perovskite solar cells with low-temperature carbon counter electrode.•Compared with Au, Ag or Pt electrodes, carbon counter electrodes are abundant, much cheaper and especially for large-scale production.•For the first time, we have a detailed study of the contact problem between perovskite and carbon layer with low temperature method.•The optimized carbon electrode with the efficiency of 7.29%, good repeatability and stability could be achieved for the perovskite solar cells.•Low-temperature carbon electrode for high efficient perovskite solar cells have the potential to realize commercialization in the near future.The low cost graphite/carbon black counter electrodes were prepared under low-temperature for hole-conductor-free mesoscopic perovskite solar cells. Different mass fraction of carbon black particles in the interspace of graphite flakes not only modulates the connection of carbon black and graphite flakes, but also guarantees the good contact between the counter electrode and perovskite layer, which obviously improves the charge transport properties of the cells. The electrochemical impedance spectra and incident photon-to-current conversion efficiency study show evidences of it. Based on the optimized low-temperature carbon electrode (LTCE) with a thickness of 5 μm, power conversion efficiency about 7.29% and good stability are achieved for the hole-conductor-free mesoscopic perovskite solar cells. The abundant availability and excellent properties of such carbon materials based LTCEs offer a wide prospect for its further applications in perovskite solar cells.

Titanium dioxide (TiO2) with dispersed W-doping shows its capability for efficient electron collection from perovskite to TiO2 in perovskite solar cell. The conduction band (CB) of TiO2 moves downward (positive shift) with increasing the tungsten (W) content, which enlarges the energy gap between the CB of TiO2 and the perovskite. Thus, the efficiency of electron injection from perovskite to TiO2 is increased. Due to the increased electron injection, W-doped TiO2 (≤0.2% W content) enhances the short-circuit photocurrent (Jsc) of perovskite solar cell and improves the performance of perovskite solar cell. Perovskite solar cell with 0.1% W-doped photoanode obtains the highest power conversion efficiency (η = 10.6%), which shows enhancement by 13% in Jsc and by 17% in η, as compared with the undoped TiO2 perovskite solar cell.

•Perovskite solar cells using F4-TCNQ doped spiro-MeOTAD layers was reported.•The F4-TCNQ dopant changes the spiro-MeOTAD conductivity and HOMO energy.•The F4-TCNQ doped spiro-MeOTAD endows the device high efficiency and stability.•An enhanced PCE of 10.59% was achieved.We report planar heterojunction perovskite solar cells with tetrafluoro-tetracyanoquinodimet-hane (F4-TCNQ) doped spiro-MeOTAD by solvent treatment as hole transport layer. The non-hygroscopic F4-TCNQ doped spiro-MeOTAD plays the same role as Li-bis (trifluoromethanesulfonyl) imide doped spiro-MeOTAD in perovskite solar cells, endowing the device both high efficiency and good stability. The F4-TCNQ dopant was optimized to enhance the conductivity and adjust the highest occupied molecular orbital of spiro-OMeTAD to match the valence band maximum of perovskite for efficient hole extraction, which results in a high fill factor, open circuit voltage and short current density, simultaneously. Device including the F4-TCNQ doped spiro-MeOTAD exhibits a power conversion efficiency of 10.59%, which is a 160% improvement relative to that of the control device with the pristine spiro-MeOTAD as hole transport layer. Time-dependent solar cell performance measurements revealed significantly improved air stability for perovskite solar cells with the F4-TCNQ doped spiro-MeOTAD hole transport layer.Planar heterojunction perovskite solar cell with tetrafluoro-tetracyanoquinodimet-hane (F4-TCNQ) doped spiro-MeOTAD by solvent treatment as hole transport layer was demonstrated. The device exhibits a power conversion efficiency of 10.59% and significantly improved air stability.

Thin film solar cells can work efficiently by successful interfacial charge separation/collection. The solution-processed perovskite (CH3NH3PbI3) film carries many trap states on the surface, which is detrimental to the high performance of solar cells. Therefore, it is of great urgency to control the interface in the device. In this study, polar silane molecules with amino end groups are self-assembled at the interface of the perovskite/hole transport materials, which works efficiently for the cells even without enough thermal annealing. It reforms the surface of the insufficiently annealed perovskite film, which leads to a normally performing solar cell without the S-shaped current density–voltage curve. For sufficiently annealed perovskite film, the small amount of PbI2 formed and a Si–O–Si network at the interface passivates the surface traps and acts as an energy barrier to reduce recombination in the perovskite solar cells. With the amino-ended silane modification, the optimized performance of the perovskite solar cell reaches 11.8%, which shows great advantages over the original device with a performance of 8.25% (0.92 Sun, AM1.5).

•Perovskite materials were developed via microwave radiation.•Perovskite solar cell using microwave radiation exhibits an efficiency of 10.29%.•Perovskite solar cell were performed in air condition under high humidity (∼60%).•A fast and less energy-intensive process was introduced in device fabrication.A rapid annealing technique for fabricating perovskite materials via microwave radiation in air condition is presented. A planar-heterojunction perovskite device via microwave radiation within 6 min exhibits an efficiency of 10.29%, compared to 11.08% for a 90 min heating-annealed device in inert atmosphere, which is higher than that (8.04%) of a heating-annealed device in air condition under high humidity (∼60%). We believe that the microwave annealing technique provides a fast and less energy-intensive process for fabricating ideal perovskite active layers for high performance solar cells.

Built-in field and energy band alignment decide the charge separation and transportation in perovskite solar cells. Composition change in perovskites to tune the energy states is thus valuable to try. In contrast to the equivalent substitution of Pb, here trivalent Sb is for the first time incorporated into CH3NH3PbI3, with a tuned optical band gap from 1.55 to 2.06 eV. Density function theory (DFT) calculations unveil the enlarged energy band gap and n-type doping property by Sb with more valence electrons than Pb. n-Type doping by Sb elevates the quasi-Fermi energy level of the perovskite/TiO2 and promotes electron transport in the working solar cell. Thus, the doped perovskite solar cell gains a lot in photovoltage while maintaining a high photocurrent, resulting in enhanced performance of 15.6% (0.956 sun, AM1.5). The results highlight the method of n/p-type doping of perovskites by heterovalent elements and its tunability to the energy states.

Quasi-solid-state dye-sensitized solar cells (DSSCs) fabricated with the mixed-plasticizer (MP) modified polymer electrolyte are reported in this paper. The mixture of hydroxyethyl methylacrylate (HEMA) and ethylene glycol (EG) as plasticizer are added into the original composite polymer electrolyte (CPE) based on poly(ethylene oxide)/poly(vinylidene fluoride-hexafluoropropylene) (PEO/P(VDF-HFP)) and KI/I2. The olefinic bonds in HEMA and hydroxyl bonds in EG provide strong molecular polarity to effectively reduce the crystallinity of the polymer electrolyte, thus largely improve the ionic conductivity of the CPE. On account of MP, the decrease of crystallinity provides a better photovoltaic performance, the best photon-to-current conversion efficiency is 6.79% with a short current density Jsc of 15.23 mA cm−2 under AM 1.5 illumination. Fourier transforms infrared (FT-IR), differential scanning calorimetry (DSC), ionic conductivity, electrochemical impedance spectroscopy are test to analyze superior property of DSSCs assembled with MP-modified CPEs. It shows that the performance of the CPEs can be largely improved by MP.

•Perovskite films treated by two annealing methods were compared.•Annealing temperature and duration greatly affected perovskite films.•Slow annealing resulted in high-efficient perovskite solar cells.•The slow annealing device showed the best efficiency of 13.58%.The morphology, structure, optical and electrical properties of perovskite films treated by two different annealing methods with different annealing temperature ramp and their corresponding device performance have been studied and compared. Annealing temperature ramp significantly influences the surface morphology and optical properties of perovskite films which determines the performance of solar cells which determines the performance of solar cells. The perovskite films treated by one-step direct annealing method tend to exhibit irregular and weak ultraviolet–visible absorption spectrum, which can easily result in great variation in the final performance of solar cells. While multi-step slow annealing is beneficial for preparing highly uniform and well-crystallized perovskite films, and thus these devices present tightly-distributed performance parameters. The best device treated by multi-step slow annealing method showed a short circuit current density of 21.49 mA/cm2, an open circuit voltage of 0.988 V, a fill factor of 64.86%, and a power conversion efficiency (PCE) of 13.58%, which is a 57% enhancement of the overall PCE relative to 8.65% of the device treated by one-step annealing method. These findings suggest that optimized slow temperature ramp is necessary to prepare high-efficient and well-reproducible perovskite solar cells.In this article, multi-step slow annealing is adopted for preparing highly uniform perovskite films and high-efficient and well-reproducible planar perovskite solar cells that present tightly-distributed performance parameters.

Depositing pinhole-free perovskite films is of vital importance for achieving high performance perovskite solar cells, especially in a planar heterojunction device. Here, perovskite films with coverage approaching 100% and with highly oriented crystal domains were obtained by carefully controlling the annealing temperature and duration. Perovskite solar cells with an average efficiency of 12% and a maximum efficiency of 15.17% were achieved in a planar heterojunction structure. Comprehensive characterization and analysis showed that appropriate annealing temperature and duration allowed the perovskite crystals to grow slowly, resulting in highly oriented crystal domains without any internal voids or pinholes. The anisotropic transport properties of perovskite crystals ensure efficient electron and hole transport to their corresponding electrodes.

•ITO-free polymer solar cells (PSCs) were fabricated by dip coating method.•Highly conductive PEDOT:PSS films used as anode were prepared.•The ITO-free PSCs performance was comparable with that of the spin coated devices.•Our results suggest the possibility of replacing ITO with dip coated PEDOT:PSS.The fabrication of anodes and active layers by dip-coating in indium tin oxide (ITO)-free polymer solar cells (PSCs) is investigated. A highly conductive poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) layer was used as an anode while a blend film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was employed as an active layer. The transmittance and sheet resistance of dip-coated PEDOT:PSS layers prepared with different thickness were studied. These layers were integrated into PSCs. The PSCs with the dip-coated PEDOT:PSS and P3HT:PCBM films exhibited power conversion efficiencies of 3.21% and 3.03% on glass and polyethylene terephthalate substrates, respectively, comparable to those of conventional ITO-based cells. Our research results suggest the feasibility of fabricating PSCs without a traditional spin-coating process and the possibility to substitute the ITO electrodes for conducting polymer films using the facile dip-coating method.

Core–shell TiO2 microspheres were synthesised by a one step solvothermal method in ethanol solvent. The single anatase TiO2 core–shell structure exhibited high reflectance and large surface area due to its special structure. When applied in the dye-sensitized solar cells (DSCs), this micro-spherical core–shell structure effectively enhanced light harvesting and led to the increase of the photocurrent of the DSCs. As a result, 29% improvement in conversion efficiency of DSCs was achieved after introducing the core–shell TiO2 scattering layer. A comparative experiment between the core–shell structure and a solid structure further confirmed that the core–shell structure is more beneficial for light scattering and photovoltaic performance. The excellent properties of the microspherical core–shell TiO2 make it a promising candidate as a scattering material for DSCs.

•Surface traps and bulk traps in the photoanodes of DSSCs are distinguished in this work.•The influence of each trap state to the electron transport is characterized.•Bulk trap states should be avoided during photoanode preparation to get high quality DSSCs.•Interface recombination time is closely related to the property of the trap states.Trap states play important role in electron transport of dye sensitized solar cells (DSSCs). Different trap states (surface and bulk traps) contribute differently to the performance of DSSCs. However, there is a lack of classification of the trap states, especially in recent doping works of the photoanodes. In this work, the Ce4+ (0.3, 0.6 and 0.9% molar ratio) in TiO2 and Ti4+ (15, 40 and 70% molar ratio) in SnO2 are assigned to surface traps and surface-and-bulk coexisted traps, respectively. The property of each trap state and its influence to the electron transport are characterized. Both the surface and bulk traps deteriorate the electron transport in DSSCs, however, the negative role of surface traps can easily be eliminated by surface modification in contrast to the bulk traps. Furthermore, contrary to the literature that the trap states will accelerate the interface recombination, it is found that the interface electron recombination time is prolonged with Ce4+ surface traps in TiO2 and Ti4+ bulk traps in SnO2, indicating that the recombination time is closely related to the property of the trap states.

Laminar cobalt sulfide (Co3S4) nanosheets are successfully deposited on fluorine doped tin oxide (FTO) substrates by a facile one-step hydrothermal method. When it was applied to dye sensitized solar cells as the counter electrode (CE), the laminar Co3S4 electrode, consisting of interconnected nanosheets, exhibits prominent catalytic activity and outstanding metallic conductivity. It is the special structure that facilitates the electron transfer and reduces interface resistance. Under one sun (100 mW cm−2) illumination, the dye-sensitized solar cell with the Co3S4 CE shows comparable photovoltaic conversion efficiency (Eff = 7.19%) to that with a Pt CE (Eff = 7.27%). The results indicate that the in situ hydrothermal method and the prepared novel laminar Co3S4 CE has potential for developing low-cost and high-efficient counter electrodes.

Quasi-solid-state dye-sensitized solar cells (DSSCs) are fabricated using tetraethylammonium tetrafluoroborate (Et4NBF4)-modified poly(ethylene oxide)/poly(vinylidene fluoride-hexafluoropropylene) (PEO/P(VDF-HFP)) composite polymer electrolytes (CPEs) along with KI and I2. Compared to the original CPE, the addition of Et4NBF4 mainly changes the conformation of the polymer structure, reduces the crystallinity of the polymer electrolyte specifically, and hence, increases the triiodide diffusion coefficient and the ionic conductivity, leading to the notable improved photovoltaic performance of DSSC. The DSSC based on the Et4NBF4 (0.15 g)-modified CPE exhibits the best performance, with a short current density of 14.70 mA cm−2 and a photoenergy conversion efficiency of 6.243% under an irradiance of 96.17 mW cm−2.

A PEO/P(VDF-HFP) polymer-blend electrolyte is modified by different amounts of LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfone)imide, LiTFSI). Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) are carried out to examine the configuration changes of the polymer electrolyte. LiTFSI acts as a plasticizer influencing the ionic conductivity of the LiTFSI-modified polymer electrolyte, and improves the short-circuit photocurrent effectively. The electrochemical impedance spectroscopy (EIS) indicates that the intercalation or adsorption of overdose Li+ to the TiO2 photoanode surface positively changes the Fermi energy level and the conduction band. This improves the interface recombination in the DSSC and reduces the open-circuit voltage. With moderate LiTFSI content (0.05 g, nKI/nI2 = 7:1) modification, the DSSC exhibits a 1.6 mA cm−2 improvement of current density and an improved performance of 5.03% compared with 4.51% of the original DSSC.

Quasi-solid-state dye-sensitized solar cells (DSSCs) are fabricated using acetamide-modified PEO/P(VDF-HFP) composite polymer electrolytes (CPEs) along with KI and I2. The DSSC assembled with acetamide-modified CPE shows higher open-circuit voltage and higher short-circuit photocurrent density than those of DSSC with unmodified CPE. With moderate acetamide content (0.20 g) modification, the DSSC exhibits a 14.3 mV improvement of photovoltage, a 2.83 mA cm−2 improvement of current density and a improved performance of 6.04% compared with 4.68% of the original DSSC. Variations in the Voc and Jsc are explained in terms of shift of the flat band potential of TiO2 and a complex formation between I3- and –NH2 of acetamide in the electrolyte.Graphical abstractHighlights► Acetamide deprotonates the TiO2 photoanode surface leading to the increased Voc. ► The short-circuit photocurrent was enhanced effectively after acetamide is added. ► The efficiency of DSSC with this acetamide-modified electrolyte was up to 6.04%.

Using the continuum self-consistent field theory (SCFT), the adsorption of flexible homo-polymers onto the surfaces of two identical cylinders immersed in a neutral polymer solution is studied. The effects of various system parameters (the chain length, the radius of the cylinders, the number density of objects, the intensity of short-region field, etc.) on the bridging chain conformation and the total amount of the adsorbed chains are investigated. The efficient multigrid method is adopted to solve the modified diffusion equation. The “masking” technique is applied to deal with the interface between the cylinders and the polymer solution, which enables the use of the Cartesian grid. Simulation results show that, the total amount of the adsorbed chains scales linearly with respect to the radius of the cylinders. On the other hand, the total amount of the bridging chain conformation does not follow a linear scaling relation with the radius of the cylinder due to the curvature effect of the cylinders. Simulation results reveal that, the total amount of the bridging chain conformation increases with both the chain length and the strength of the short-range attractive interaction between the object surface and the monomers, but eventually saturates.Graphical abstract

In this paper, we used combined self-consistent-field and hybrid particle-field theory to explore the self-assembly behavior of diblock copolymer−nanoparticle mixtures confined between two concentric circular walls. The simulation reveals that the structural frustration, the loss of conformational entropy of the copolymer, and the radii of the two concentric circles have great influence on the morphologies of the system. We also discusss the underlying mechanism of controlling the self-assembly of such a system in terms of enthalpic interaction between particles and copolymers, steric repulsive interactions between particles, and the conformational entropy of copolymers, and a representative phase diagram in terms of block ratio and the particle volume fraction is constructed. This study suggests a route to help experimentalists better create high-performance nanodevices.Keywords: confinement effects; diblock copolymer; hybrid particle-field theory; nanoparticle; self-assembly; self-consistent field theory

The anatase TiO2 hollow spheres with diameter of 500 nm and shell thickness of 25 nm are embedded in P25 TiO2 nanocrystalline photoanodes to improve the light scattering ability of the photoanode. Photoanodes embedded with different contents of TiO2 hollow spheres are prepared and the profiles of the photoanodes are systematically characterized. It is found that the morphologies of the photoanodes were modified by the TiO2 hollow spheres. With increasing the TiO2 hollow spheres’ contents, the light scattering ability of the modified photoanodes is effectively improved, while the dye adsorption decreases. By optimizing the TiO2 hollow spheres’ content in TiO2 nanocrystalline, a higher performance of the DSSC (Jsc = 16 mA cm−2, Voc = 0.72 V, FF = 0.648 and η = 7.59%) is obtained compared with the pure TiO2 nanocrystalline DSSC (Jsc = 13.96 mA cm−2, Voc = 0.686 V, FF = 0.684 and η = 6.67%, measured at 98.3 mW cm−2, AM1.5). The improved performance is mainly due to the enhanced light scattering by the TiO2 hollow spheres. The open circuit voltage of the hollow spheres modified DSSCs is higher than that of the DSSC with pure P25 photoanode, which can be attributed to the fact that TiO2 hollow spheres substitute of the TiO2 nanocrystallines and reduce the interface recombination by decreasing the surface charge trap-site density of the photoanodes.

The formation of vesicles in a binary blend of an amphiphilic diblock copolymer AB/homopolymer C was studied in a dilute solution using the real space two-dimensional self-consistent field theory (SCFT). Special attention was played to the role played by the homopolymer C in controlling the vesicle formation. In the simulations, it was found that as the averaged volume fraction of homopolymer C was decreased while keeping the total averaged volume fraction of block copolymer AB and homopolymer C unchanged, there was a morphological transition from the bilayer vesicles to rod-like/circle-like micelles. The compound vesicle structure was observed in the simulations. When the averaged volume fraction of block copolymer AB was further increased while the total averaged volume fraction of AB and C remained unchanged, the compound vesicle structure became less favored entropically than the unilamellar vesicle structure. The effect of the degree of polymerization of the homopolymer C on the vesicle formation of the amphiphilic system was examined. By reducing the degree of polymerization of the homopolymer C to unity, the component C became a small solvent molecule immiscible with the bulk solvent. It was found that the small solvent C exerted no influence on the morphological stability of the vesicles.

The complex microstructures of bidisperse nanoparticles/diblock copolymer mixtures in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory (SCFT) and the density functional theory (DFT). Special attention is payed to the role played by the block ratio and the interaction parameters between each component in the mixture. It is shown that the conformational entropy of the polymer chains, the block ratio of the diblock copolymer, the chemical difference between two kinds of particles and the steric packing effect of the particles play important roles in determining the morphologies of the systems. It is found that with the increase of the block ratio, the mixture undergoes a morphological transition from compound micelles to spherelike micelles. The increase of chemical difference between the two kinds of particles can promote the formation of “a jujube set in a cake”. When the selectivity of the particles is changed, another type of micelle emerges. Specifically, in the case where the particles are nonselective to the A- and B-blocks, ordered structures from the phase separation between the two types of particles emerge inside the micelles formed by the amphiphilic diblock copolymers in solutions.

We perform first principles density functional theory calculations to investigate the geometric and electronic structures of Tin−mH2 (n = 2−7, and m = 1−22). By optimizing geometric structures, we obtain the saturated configurations for hydrogen storage on small Tin (n = 2−7) clusters. Interestingly, we find that with an increase in the size of the Tin cluster, the effective space for each titanium atom to adsorb hydrogen molecules decreases, as does the maximum amount of hydrogen molecules adsorbed on each titanium atom. When the size of the Tin cluster goes beyond n = 5, the maximum number of hydrogen molecules adsorbed on each Ti atom keeps a constant of 3. For Ti7−mH2 clusters, the average Mulliken charges increase at first and decrease afterward, the binding energy EbH per atom of H increases when the hydrogen molecule number m changes from 1 to 3, and then, it shows a slow decrease with m increasing from 3 to 21. Furthermore, we suggest/propose that the hybridization of atomic orbitals in different atoms could be used to estimate the type of the bonds between the different atoms in clusters. As the Tin−mH2 clusters get bigger, due to the charge density redistribution, the interaction between titanium atoms becomes weaker and the bond length of Ti−Ti increases gradually. Meanwhile, the H−H bonds are elongated or even broken. The geometry of the host cluster is distorted from D5h into C3v when 21 H2 molecules are chemisorbed.

•An ultrathin and discrete TiO2 (u-TiO2) was fabricated at low temperature.•High-performance perovskite solar cells based u-TiO2was realized.•u-TiO2 between perovskite and FTO functions as a bridge for electron transport.•u-TiO2 accelerates electron transfer and alleviates charge recombination.A compact TiO2 (c-TiO2) layer fabricated by spin coating or spray pyrolysis following a high-temperature sintering is a routine in high-performance planar heterojunction perovskite solar cells. Here, we demonstrate an effective low-temperature approach to fabricate an ultrathin and discrete TiO2 (u-TiO2) for enhancing photovoltaic performance of perovskite solar cells. Via hydrolysis of low-concentration TiCl4 solution at 70 °C, u-TiO2 was grown on a fluorine doped tin oxide (FTO) substrate, forming the electron selective contact with the photoactive CH3NH3PbI3 film. The perovskite solar cell using u-TiO2 achieves an efficiency of 13.42%, which is compared to 13.56% of the device using c-TiO2 prepared by high-temperature sintering. Cyclic voltammetry, steady-state photoluminescence spectroscopy and electrical impedance spectroscopy were conducted to study interface engineering and charge carrier dynamics. Our results suggest that u-TiO2 functions as a bridge for electron transport between perovskite and FTO, which accelerates electron transfer and alleviates charge recombination.

Core–shell TiO2 microspheres were synthesised by a one step solvothermal method in ethanol solvent. The single anatase TiO2 core–shell structure exhibited high reflectance and large surface area due to its special structure. When applied in the dye-sensitized solar cells (DSCs), this micro-spherical core–shell structure effectively enhanced light harvesting and led to the increase of the photocurrent of the DSCs. As a result, 29% improvement in conversion efficiency of DSCs was achieved after introducing the core–shell TiO2 scattering layer. A comparative experiment between the core–shell structure and a solid structure further confirmed that the core–shell structure is more beneficial for light scattering and photovoltaic performance. The excellent properties of the microspherical core–shell TiO2 make it a promising candidate as a scattering material for DSCs.

Depositing pinhole-free perovskite films is of vital importance for achieving high performance perovskite solar cells, especially in a planar heterojunction device. Here, perovskite films with coverage approaching 100% and with highly oriented crystal domains were obtained by carefully controlling the annealing temperature and duration. Perovskite solar cells with an average efficiency of 12% and a maximum efficiency of 15.17% were achieved in a planar heterojunction structure. Comprehensive characterization and analysis showed that appropriate annealing temperature and duration allowed the perovskite crystals to grow slowly, resulting in highly oriented crystal domains without any internal voids or pinholes. The anisotropic transport properties of perovskite crystals ensure efficient electron and hole transport to their corresponding electrodes.