•Systematically studies on the influence of amine salts on the crystalline and optoelectronic properties of perovskite films.•The CH3NH3PbX3-yIy (X = Cl, Br) films are obtained by exposing PbI2 in different amine salts vapor.•Based on the MAPbI3-yCly (y ≈ 0) film, best efficiency of 17.3% is achieved on planar PSC with good stability over 3600 h.The halide-mixed CH3NH3PbX3-yIy (X = Cl, Br) (MAPbX3-yIy) films have tunable band gaps for applications in perovskite solar cells (PSCs). The performances of PSCs can be further adjusted by halide mixing of perovskite films. Preparing the MAPbX3-yIy films by low pressure vapor-assisted solution process (LP-VASP) could achieve pin-hole free perovskite films, which has the potential to mass production of perovskite films. In this study, the MAPbX3-yIy (X = Cl, Br) thin films are prepared by exposing PbI2 films in various amine salts vapor and applied to fabricate the planar PSCs. Systematical structural-property investigations on the MAPbI3-yXy (X = Cl, Br) thin films demonstrate that the halide-mixed perovskite films could be achieved by adopting different amine salts. The MAPbI3/MAPbCl3 biphasic constitution is observed in perovskite films using pure MACl, while the MAPbI3-yCly (y ≈ 0) could be obtained using MACl:MAI mixture. Using pure MABr or MABr:MAI mixture, the MAPbBr3-yIy films are prepared. The XRD and XPS results indicate that there is no remnant Cl in the MAPbI3-yCly (y ≈ 0) films, nor I in the MAPbBr3-yIy (y ≈ 0) films. Because the amine salts are excess, the halogen in amine salts mainly decide the halogen in CH3NH3PbX3 in our study. Moreover, the MAPbCl3-yIy (y ≈ 0) and MAPbBr3-yIy based PSCs are demonstrated to behave better stability than the MAPbI3 based PSC under continuous illumination at AM 1.5G. Furthermore, the planar PSCs based on 15 wt% MACl mixed MAI exhibit power conversion efficiency of 17.3% with good stability over 3600 h.Download high-res image (202KB)Download full-size image

The remnant PbI2 at the mesoporous-TiO2 (m-TiO2)/CH3NH3PbI3 interface can act as an interface modification layer for high-efficiency perovskite solar cells (PSCs). In this study, we adopted Pb(CH3COO)2·3H2O (PbAc2) to control the amount of remnant PbI2 at the m-TiO2/CH3NH3PbI3 interface. The characterization results demonstrate that the amount of remnant PbI2 could be controlled by the concentration of PbAc2 solution without influencing the crystallographic textures of CH3NH3PbI3 films. By adjusting the PbAc2 solution concentration, the optimized PSC can achieve a 15% enhancement of PCE in the case of using a two-step method for CH3NH3PbI3 preparation. Under the circumstances of using an anti-solution method, it still displayed a 10% enhancement of the average PCE for 10 individual PSCs with PbAc2 (13.6% to 15.0%). The steady-state photoluminescence (PL), time-resolved photoluminescence (TR-PL) and open-circuit voltage decay results demonstrated that the remnant PbI2 could reduce carrier recombination at the m-TiO2/CH3NH3PbI3 interface. Meanwhile, the enhancement of the open-circuit voltage was achieved for PSCs with PbAc2.

Compared to that of methylammonium lead iodide perovskite (MAPbI3), formamidinium lead iodide perovskite (FAPbI3) has a smaller energy band gap and greater potential efficiency. To prevent the transformation of α-FAPbI3 to δ-FAPbI3, preparation of (FA)x(MA)1–xPbI3 was regarded as an effective route. Usually, the planar (FA)x(MA)1–xPbI3 perovskite solar cells are fabricated by a solution process. Herein, we report a low-pressure vapor-assisted solution process (LP-VASP) for the growth of (FA)x(MA)1–xPbI3 perovskite solar cells that features improved electron transportation, uniform morphology, high power conversion efficiency (PCE), and better crystal stability. In LP-VASP, the (FA)x(MA)1–xPbI3 films were formed by the reaction between the PbI2 film with FAI and MAI vapor in a very simple vacuum oven. LP-VASP is an inexpensive way to batch-process solar cells, avoiding the repeated deposition solution process for PbI2 films, and the device had a low cost. We demonstrate that, with an increase in the MAI content, the (101) peak position of FAPbI3 shifts toward the (110) peak position of MAPbI3, the (FA)x(MA)1–xPbI3 perovskites are stable, and no decomposition or phase transition is observed after 14 days. The photovoltaic performance was effectively improved by the introduction of MA+ with the highest efficiency being 16.48% under conditions of 40 wt % MAI. The carrier lifetime of (FA)x(MA)1–xPbI3 perovskite films is approximately three times longer than that of pure FAPbI3. Using this process, solar cells with a large area of 1.00 cm2 were fabricated with the PCE of 8.0%.Keywords: mixed-organic-cation lead halide perovskite; perovskite solar cells; planar heterojunction; power conversion efficiency; vapor-assisted deposition;

•Photo polymerization induced phase separation method was used to prepare TiO2 films.•TiO2 films with three-dimensional network structure were used as photoanodes.•Energy conversion efficiency was enhanced compared to that of P25 film.•Both electrons transport and ions diffusion were promoted compared to P25 film.TiO2 electrodes with a three-dimensional interweaved network structure were fabricated on fluorine-doped tin oxide substrates for use in dye-sensitized solar cells. The structure was realized by photo-polymerization-induced phase separation. The electrodes had a continuous TiO2 skeleton and numerous interconnected macro/mesopores, which formed large three-dimensional cavity channels. The energy conversion efficiency of a dye-sensitized solar cell having the electrode was 3.01%, or 37.2% higher than that of a dye-sensitized solar cell having a P25 electrode with the same film thickness of 5 μm. The enhanced conversion efficiency can be attributed to improved electrons transport and I−/I3− ion diffusion of photoanodes having interweaved network structure.

•Di-n-alkylphosphinic acids were used as coadsorbents with indoline sensitizer D149.•We examine the effect of the different alkyl chains on DSCs performance.•The device performance was obviously enhanced with increasing the alkyl chain length.•The device efficiency was increased by about 10% with DHdPA co-adsorbed.Three di-n-alkylphosphinic acids (DPAs) with different chain lengths (1, 8, 16) were adopted as coadsorbents in dye-sensitized solar cells (DSCs) with organic sensitizer D149. The adsorption behavior of these coadsorbents on nanoporous TiO2 surface through POTi bond was confirmed by FT-IR spectra. And the performance of all devices was detected on the basis of photocurrent–voltage (J–V) characteristics and electrochemical impedance spectroscopy (EIS). It was found that the amount of dye adsorption gradually decreased with increasing alkyl chain length of DPAs, which was contributed to the competitive adsorption between dye D149 and coadsorbents. In spite of this, di-n-hexadecylphosphinic acid (DHdPA) performed best both in the improvement of short-circuit current density (Jsc) and open-circuit voltage (Voc). The increase of open-circuit photovoltage was ascribed to the negative movement of the conduction band edge and the retardation of electron recombination. Although the dye adsorption amount reduced to a great degree, the break up of dye aggregation mainly contribute to the enhancement of short-circuit current density. The overall conversion efficiency was further improved from 5.53% to 6.09% with DHdPA as the coadsorbent for D149 based device.

•The film has the particular structure, lack of bottleneck for electron transfer.•The structure is good for reducing the charges recombination.•The film showed excellent photocatalytic activity under fluorescent lamp irradiation.•The SPSS structure provides new ideas to develop new anode films of the DSSC.Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO2 films with spinodal phase separation structure (SPSS) and continuous TiO2 skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO2 films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO2 anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.

The TiO2 photoanode film with hierarchical structure which consists of porous structure and spinodal phase separation structure with macroporous continuous skeleton was fabricated by photopolymerization induced phase separation method. The influence of the different photomonomers, different coating layers and different heat treatment temperatures on the structure and photoelectric property of TiO2 film has been investigated and the possible mechanism was proposed. The performances of the TiO2 anode film were characterized by scanning electron microscopy, X-ray diffraction and I–V test. The results indicated that, in contrast with the TiO2 anode film with single structure, the as-prepared TiO2 anode film with hierarchical structure showed higher photoelectric conversion efficiency which is 0.272 %. Even though the photoelectric conversion efficiency is not very high, the strategy presented in the paper should be valuable and it still provides the ideas for the new structure and new preparation method on photoanode film of dye-sensitized solar cells, meanwhile, it lays the foundation for designing the solar cells with high photoelectric conversion efficiency.

Macroporous TiO2 films have been fabricated by a photo polymerization-induced phase separation method without any surfactant and colloidal templates. The gel TiO2 films deposited from the precursor solution containing photo monomer dipentaerythritol pentaacrylate were irradiated by the ultraviolet light. After that, the films were heat-treated at 600 °C for 10 min. The scanning electron microscopy results showed that TiO2 films with macroporous structures could be obtained. The macroporous structure could be controlled by changing the reaction parameters. The as-prepared TiO2 films exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than that of the dense TiO2 film.

TiO2 films with controlled macroporous structures have been prepared from the precursor solution containing photo monomer pentaerythritol tetraacrylate by a photo polymerization-induced phase separation method (PIPS) in the absence of any surfactant and colloidal templates. The gel TiO2 film deposited from the precursor solution by dip-coating was irradiated with ultraviolet light for some time. During the irradiation process, the polymerization of the photo monomer was induced, which resulted in the phase separation in the film system. After the reaction, two phases existed in the film, one was the emerging polymer rich phase, another was the residual monomer–TiO2 oligomer rich phase. After heat-treatment at 600 °C, the entire polymer decomposed and a well-defined interconnected macroporous TiO2 films could be obtained. X-ray diffraction, scanning electron microscopy, atomic force microscopy, thermogravimetric and differential thermal analysis were used to characterize the macroporous TiO2 films. The results showed that the macroporous texture could be tuned by changing the composition of the precursor solution. The solvent evaporation was controlled by the addition of polyvinylpyrrolidone. Highly macroporous TiO2 films prepared by the PIPS method exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than the dense TiO2 film.

TiO2 films with controlled macroporous structures have been prepared from the precursor solution containing photomonomer dipentaerythritol pentaacrylate by a photopolymerization-induced phase-separation method (PIPS) in the absence of any surfactant and colloidal templates. The gel TiO2 film deposited from the precursor solution by dip-coating was irradiated with the ultraviolet light for some time. During the irradiation process, the polymerization of the photomonomer was induced, which resulted in the phase-separation in the film system. At the end of the polymerization reaction, two phases existed in the film, one was the emerging polymer rich phase, and another was the residual monomer-TiO2 oligomer-rich phase. After heat-treatment at 600 °C, the entire polymer decomposed and a well-defined interconnected macroporous TiO2 films could be obtained. X-ray diffraction, scanning electron microscopy, atomic force microscopy, thermogravimetric, and differential thermal analysis were used to characterize the macroporous TiO2 films. The results showed that the macroporous texture could be tuned by changing the composition of the precursor solution and the type of the reactive monomer. Polyvinylpyrrolidone was introduced into the system to slow the solvent evaporation. Highly macroporous TiO2 films prepared by the PIPS method exhibited much higher photocatalytic activity for the decomposition of methylene blue dye than the dense TiO2 film.