Study On Properties Of SrTiO₃Photoelectric Materials And Dye-sensitized Solar Cells

Environment and energy issues are still the bottle neck for the continuable development of humanbeing. In order to solve these problems, many researchers contribute their work to protect the environment.Semiconductor photocatalysis is an advanced technology that employs the electrons on conduction bandand holes on valence band by absorbing the photons. Pollutants can be removed via oxidization orreduction and hydrogen can be obtained via water-splitting. In view of efficient solar energy conversion,visible-light-responsive photocatalysts are important because43%of the whole solar energy is visible lightwhile only4%is UV light. In order to apply the visible-light of the solar energy, designing and developingvisible-light-responsive photocatalysts has become a hot topic in photocatalysis. SrTi03can also be used inproducing hydrogen, degrading polluted organic and photochemical cells because of its high bandgap（3.12eV）and photo-catalysis activity.In this dissertation, AgNbO₃,（AgNbO₃）0.5（SrTiO₃）0.5, SrTiO₃and Cr-doped SrTiO₃samples wereprepared by the solid-state-reaction method. Meanwhile, it discussed stability of Chromium in Cr-dopedSrTiO₃photocatalyst, band structure and photoelectrochemical properties of AgNbO₃-SrTiO₃solid solutionthin films, the influence that the amount of PEG400has on the properties of the dye sensitized solar cell.The main contents and achievements in this dissertation are as follows:The Cr-doped SrTiO₃samples were prepared by the solid-state-reaction method using the Cr2O₃, TiO2and SrCO₃as starting materials. The effect of doping amount, doping site and calcination temperature onthe stability of chromium in Cr-doped SrTiO₃were investigated. The stability of Chromium in Cr-dopedSrTiO₃was analyzed by measuring the UV-vis spectra of the solution obtained from filtering the mixture ofCr-doped SrTiO₃and aqueous solution with different pH value. The observed results indicated that themore the amount of Cr2O₃added, the more the amount of Cr₂O₃remained. The samples of Cr substitutedfor Sr in SrTiO₃is more stable than that for Ti in SrTiO₃. The higher calcination temperature is helpful forthe Cr doping reaction.AgNbO₃,（AgNbO₃）0.5（SrTiO₃）0.5and SrTiO₃films on FTO conducting glass substrates werefabricated by pulse laser deposition at873K under10Pa oxygen pressure with the laser energy of300mJ.The crystal structure, optical property and surface morphology was measured by X-ray diffractometor, UV-vis spectroscopy and atomic force microscopy. The energy band structure and photoelectrochemicalbehavior were investigated by measuring the onset potential and photocurrent. The optical band gaps forAgNbO₃,（AgNbO₃）0.5（SrTiO₃）0.5and SrTiO₃are3.1,3.3, and3.6eV, respectively. And the onset potentialfor the AgNbO₃,（AgNbO₃）0.5（SrTiO₃）0.5and SrTiO₃films are-0.34,-0.31and-0.56eV （vs. Ag/AgCl）,respectively, indicating that the valence band top becomes more positive in order of AgNbO₃,（AgNbO₃）0.5（SrTiO₃）0.5and SrTiO₃. The AgNbO₃film shows the smallest steady photocurrent density andthe largest ratio of the transient photocurrent and steady photocurrent, revealing that the photocurrent isclose to the recombination of electron and hole at surface states.The TiO₂film was obtained by scraping method. TiO2slurry was prepared by grinding the mixture ofTiO2powder （P25）, water, PEG400, dispersant acetylacetone and Triton X-100. Then the slurry wasscraped on the conductive glass plate. The TiO2film was heated at450oC for30min to remove someimpurities and produce nanoporous. TiO2/dye electrode was fabricated by immersing the nanoporous TiO2film into dye N719solution（5×10-5M）for24h. The Pt coated FTO as counter eletrode was prepared bythermal decomposition method. The cell was assembled by dropping an electrolyte solution into the spacebetween the TiO2/dye electrode and the counter eletrode. Then the performance test was carried onelectrochemical workstation CHI660. The results show that there are better photoelectric properties underthe condition of adding0.2mL PEG400, heat treatment at450oC for30min, immersed in the N719solution （5×10-5M） for24h of the TiO₂film.