The Photoelectricity Properties Of Porous Silicon And Titanium Dioxide Composite Films

The photoelectric catalysis of semiconductor as a very efficient technology can solve environment problems and energy crisis in recent years.The material selection and the surface modification are key steps to improve photoelectric catalysis of semiconductor photoanode.It is the hot topic that how to stably and efficiently improve the photoelectric catalysis efficiently in this field.In order to effectively improve the photoelectrochemical performance of semiconductor composite thin-films photoanode,we concentrated on the porous Si/TiO2composite thin-film photoanodes and the shape-controlled synthesis of the porous Si microstructures and TiO2 nanowires in this thesis.The research work has been carried out to improve the utilization of light from composite thin-film photoanodes and enhance the transmission and separation of photogenerated carriers.The main research are as follows:The preparation process of the porous Si is based on the metal-assisted chemical etching and using silver particles as the noble metal catalyst.By changing the concentration of AgNO3during the deposition and the etching time during the etching process,porous Si samples with different microstructures were prepared.The SEM results show that different AgNO3deposition concentrations and etching times have a great influence on the microstructure of porous Si samples.The DRS test results show that the porous Si sample with 0.01M AgNO₃and etching time for 35min has the best anti-reflection performance.It explained with the principle of the etching reaction diagram.In order to research the effect of different porous Si samples on the performance of porous Si/TiO2 composite thin-film photoanodes,porous Si/TiO2 composite thin-film photoanodes were prepared by hydrothermal synthesis on porous Si samples with different morphology.The SEM and XRD results show that different microstructures of porous Si affect the growth morphology of TiO2 nanowires,and most of TiO2 nanowires are rutile.In addition,the DRS test results show that the composite thin-film photoanode which based on the porous Si sample with 0.01M AgNO₃ and etching time for 35min also has excellent anti-reflection properties.Besides,the photoelectrochemical test results show that this porous Si/TiO₂ composite thin-film photoanode also has a higher photocurrent and photoelectrocatalytic activity.According to the anti-reflection effect diagrams of different composite thin-film photoanode samples and photoelectrocatalytic principle diagrams,it is believed that porous Si with excellent antireflection properties can improve the light utilization of the composite thin-film photoanode and can effectively enhance the photogenerated electron-hole pair generation ability,and ultimately improve the photoelectrochemical properties of porous Si/TiO2composite thin-film photoanode.In order to research the effect of different TiO₂ nanowires on the performance of porous Si/TiO2 composite thin-film photoanodes,the hydrothermal growth time of TiO2 nanowires was changed,and the porous Si/different TiO2 composite thin-film photoanodes were prepared.SEM results show that the size of TiO2 nanowires increase with the hydrothermal growth time.And the DRS test result show that the composite thin-film photoanode with hydrothermal growth for 8h has the strongest UV absorption.However,the photoelectrochemical tests show that the porous Si/different TiO₂ composite thin-film photoanode with hydrothermal growth for 6h has the higher photocurrent and photoelectrocatalytic activity.It is believed that increasing the thickness of the TiO2 nanowire layer can effectively improve the UV utilization efficiency of the composite thin-film photoanode,but the excessively TiO2 nanowire layer will lead to the photoelectron-hole pair recombination ahead of time,and the quantum efficiency of the photoanode will be reduced,which is not good to the photoelectrochemical performance of porous Si/TiO₂ composite thin-film photoanodes.In order to evaluate the photoelectrochemical properties of the porous Si/TiO₂ composite thin-film photoanode,we also performed the porous Si,Si/TiO₂ composite photoanodes and silicon wafer.The DRS test results show that the porous Si/TiO₂ composite thin-film photoanode has the best anti-reflection performance.The environment illumination and bias voltage conditions during the photoelectrochemical test were adjusted.The photocurrents,photoelectric catalysis?PEC?,directly photo catalysis?DP?under simulated solar light and visible light irradiation were performed,and the electric catalysis?EC?also be performed.The results show that the porous Si/TiO2 composite thin-film photoanode showed the best photoelectrochemical performance in all tests,besides the PEC activity under the simulated sunlight has the best catalytic activity.Due to the heterostructure effect,the construction of n-type porous Si and TiO2 nanowires increases the transmission efficiency of charge carriers and the separation efficiency of electron-hole pairs,and the separation efficiency further increased under the applied bias voltage.Meanwhile,the window effect increases the utilization of simulated solar light.Finally,the photoanode of porous silicon/TiO2 composite film has the best photoelectrochemical performance.