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Mesoporous TiO2 photoanodes are prepared by an electrophoretic deposition (EPD) method and applied in dye‐sensitized solar cells (DSSCs). Pretreating an F‐doped SnO2 coated glass (FTO) substrate and post‐treating a TiO2 film to introduce an anatase TiO2 layer on the FTO and the TiO2 film, respectively, can greatly improve the power conversion efficiency (PCE) of a DSSC, which constitutes up 31% improvement compared with the untreated device. To disclose the mechanism for improvement, scanning electron microscopy, electrochemical impedance spectroscopy, open‐circuit voltage decay, and photoluminescence spectra are investigated. It is proposed that the preformed compact TiO2 layer can suppress the back recombination by preventing direct contact between the electrolyte and the FTO substrate. Moreover, the compact TiO2 layer can reduce contact resistance between FTO and TiO2 particles. Further increased PCE by post‐treatment is attributed to the promoted charge transfer efficiency. Both pre‐ and post‐treating strategies can offer a reference to enhance the PCE for other porous film‐based DSSCs, as well as promote the application of EPD in DSSCs. [ABSTRACT FROM AUTHOR]

A TiO 2 compact layer was coated on fluorine-doped tin oxide (FTO) glass substrate prior to deposition of SnO 2 nanocrystalline thin film to suppress backflow of electrons from FTO to the SnO 2 nanocrystalline thin film. The resultant thin film was used as a photoelectrode to fabricate dye-sensitized solar cell. For comparison, a SnO 2 compact layer was also prepared to discuss the effect of the TiO 2 compact layer on the electron backflow process. Compared with the dye-sensitized SnO 2 nanocrystalline thin film solar cell without the compact layer, light-to-electric conversion efficiency for the solar cell with the TiO 2 compact layer was improved by 82.1% and it was even improved by 41.7% compared with the cell with the SnO 2 compact layer. Electrochemical impedance spectroscopy and open-circuit voltage decay of dye-sensitized solar cells were measured to demonstrate the improvement mechanism due to the TiO 2 compact layer. Both recombination resistance at the photoelectrode/electrolyte interface and lifetime of electrons on the SnO 2 nanocrystalline thin film were increased due to introduction of the TiO 2 compact layer. Because the conduction band of TiO 2 is higher than that of SnO 2 , the TiO 2 compact layer acts as not only a physical barrier to separate FTO substrate from electrolyte, thus suppressing recombination of electrons on FTO with the electrolyte, but also a potential barrier to effectively block the backflow of electrons from FTO substrate to the SnO 2 thin film. [ABSTRACT FROM AUTHOR]

Compression and incorporated graphene significantly improve light transmittances and charge transport properties of an opaque and poor internal-connected mesoporous photoanode, as well as improve the PCE of the corresponding device. Semi-transparent TiO 2 /graphene photoanodes are prepared at room temperature via an electrophoretic deposition method followed by compression and applied in dye-sensitized solar cells (DSSCs). Compression enhances the power conversion efficiency (PCE) of a DSSC, which constitutes up 18.4 times improvement compared to the uncompressed device. Incorporating graphene into the compressed film further improves the PCE by 28.8%. Simultaneously, compressing and graphene incorporating can greatly increase the film's transmittance at long wavelengths, benefiting to the use of DSSCs as front unit in tandem solar cells. Scanning electron microscopy, porosity measurements, electrochemical impedance spectroscopy and open circuit voltage decay are performed to investigate the mechanisms. It is demonstrated that compressing a film can reduce the porosity and improve the inter-particle connections, which accounts for the increased light transmittance and enhanced PCE. The incorporated graphene can provide extra charge carrier pathway due to its excellent charge transport properties, as well as protect TiO 2 nanostructure by preventing film cracking upon pressing due to its good flexibility, thus increases PCE to 6.75%, which, to our best knowledge, is the highest value among DSSCs with room-temperature prepared photoanodes. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) light with a wavelength of 172 nm has the capacity to convert the oxygen contained metal organic precursor into metal oxide. Here, zinc acetate precursor thin film is directly converted into ZnO thin film by the irradiation of 172 nm VUV light rather than the high temperature sintering. The converting processes were demonstrated by the measurements of FTIR, XRD, SEM and XPS. And then the effect of irradiating time on the morphology, thickness and transparence of the prepared ZnO thin films was discussed. The ZnO thin film was further used as the compact layer in the photoelectrode of dye-sensitized solar cell (DSSC) to suppress the recombination processes of photogenerated electrons on the conducting glass electrode. For the different irradiation times, the photoelectric conversion efficiency of DSSC based on the compact layer prepared by the irradiation for 30 min is the highest reaching 10.27%, which is also higher than that of DSSCs without the compact layer and even with the compact layer prepared by the high temperature sintering. The uniform, dense, pinhole-free and amorphous ZnO thin film on the conducting glass substrate can be successfully prepared using the VUV irradiation technology for the compact layer of DSSCs. The ZnO compact layer prepared by the VUV light of 172 nm from zinc acetate precursor thin film shows better performance than the sintered layer for the photoelectrode of dye-sensitized solar cell. [Display omitted] • ZnO compact thin film is prepared by 172 nm VUV irradiation from zinc acetate. • ZnO thin film is used as a compact layer in photoelectrode of DSSCs. • The compact layer prepared by VUV irradiation is better than the sintered layer. [ABSTRACT FROM AUTHOR]

Quaternary Cu 2 ZnSnS 4 (CZTS) nanocrystalline thin films were in situ grown on FTO coated conductive glass by a low cost solvothermal method. The effect of the reaction time and the concentration of precursor solution on the purity and morphologies of the deposited thin films was studied. The morphology, crystal structure and composition of the deposited thin films were characterized by scanning electron microscope, high resolution transmission electron microscope, X-ray diffraction, Raman spectroscopy and energy-dispersive X-ray spectroscopy. The pure wurtzite CZTS nanoparticles can be formed as the reaction time is 20 h. The film prepared at the optimized precursor solution concentration has uniform thickness, smooth surface and tight binding between the nanoparticles. The performance of the deposited CZTS thin films used as the counter electrode for dye-sensitized solar cells (DSSCs) was evaluated by measuring photocurrent density-voltage curves of DSSCs, electrochemical impedance spectroscopies and Tafel polarization curves of the symmetric cells. Photoelectric conversion efficiency of DSSC based on the optimized CZTS counter electrode reached 6.19%. The excellent photoelectric performance is attributed to the better surface morphology and conductive skeleton of the prepared CZTS thin film. The in situ solvothermal preparation method of the CZTS thin films for counter electrode of DSSCs is green, low cost and simple. Cu 2 ZnSnS 4 thin film in situ deposited on FTO substrate by a low cost solvothermal method has good microstructure and catalytic activity to the iodide reduction to be used as a high efficient counter electrode of dye-sensitized solar cells. Image 1 • Cu 2 ZnSnS 4 thin film is in situ deposited on FTO substrate by a low cost solvothermal method. • Cu 2 ZnSnS 4 film is well adhered to the substrate to greatly reduce the inactivation interface. • As CE of dye-sensitized solar cells, Cu 2 ZnSnS 4 film has equivalent catalytic activity to Pt. [ABSTRACT FROM AUTHOR]

BaTiO 3 is used to fabricate the electron transport layer of perovskite solar cells due to its spontaneous polarization. Li+ ions were doped into BaTiO 3 by the hydrothermal synthesis to increase the spontaneous polarization. The particle size of the as-prepared BaTiO 3 nanoparticles becomes smaller and more uniform for doping of Li+ ions with a molar ratio of 1.0 during the synthesis processes. The absorption edge shifts towards the short wavelength with the increase in the doping amount. Further, TiO 2 nanocrystalline thin film was deposited on the Li-doped BaTiO 3 thin film, the double layer was used as an electron transport layer of perovskite solar cell to indirectly demonstrate the effect of doping on the spontaneous polarization of BaTiO 3. The perovskite solar cell based on BaTiO 3 with 1.0 doping molar ratio of Li+ ions shows the highest light-to-electric conversion efficiency of 14.3% accompanying with the highest short-circuit photocurrent density. The measurements of impedance spectra and intensity modulating photocurrent spectra indicate that the photocurrent enhancement of perovskite solar cells is attributed to the spontaneous polarization enhancement of Li-doped BaTiO 3 thin films. The enhanced internal electric field in the BaTiO 3 thin layer accelerates the photogenerated electron transport in the electron transport layer of perovskite solar cell. Image 1 • The Li+ doping affects spontaneous polarization on BaTiO 3. • The spontaneous polarization in Li-doped BaTiO 3 promotes the electron transport. • Li-doped BaTiO 3 in electron transport layer improves performance of perovskite solar cell. [ABSTRACT FROM AUTHOR]