Preparation Of Polyoxometalate/quantum Dot/TiO₂ Nanotube And Application In Quantum Dot Sensitized Solar Cell

People regard solar energy as the cleanest sustainable energy.At present,the development of solar cells is in the ascendant,and quantum dot sensitized solar cells（QDSSCs）have attracted considerable attention.Ti O₂ is superior to other semiconductor materials in photoelectric properties,stability and price.One-dimensional Ti O₂nanotubes have a large specific surface area and can carry more photosensitizers,and the ordered nanotubes can be used as a fast transmission channel for photogenerated electron.However,Ti O₂with large band gap can only absorb 4%～6%of the total amount of sunlight,which can not effectively use solar energy and the recombination of electron-hole pairs,resulting in low photoelectric conversion efficiency.Polyoxometalates（POMs）,as a unique class of semiconductors,can be used as a link to accelerate the electron transport and inhibit the electron-hole recombination.Moreover,the structure of POMs remains unchanged after multi-electron transfer,which has a very high application value in the photovoltaic field.It is proved that polyoxometalates can optimize the photoelectric properties of Ti O₂,but there is a big limitation to improve the conversion rate by using polyoxometalates as photosensitizer alone.Semiconductor quantum dots act as electron providers,broadening the spectrum of absorption.Therefore,in order to solve the problems of narrow light absorption range and electron-hole recombination of Ti O₂nanotubes,polyoxometalates（POMs）and quantum dots（QDs）were used as photosensitizers to improve the photoelectric properties of Ti O₂ nanotube.Based on this,the following three parts of the exploration:TiO₂ nanotubes with pore size of about 100 nm and wall thickness of about 20 nm were prepared by anodic oxidation.Si W₁₂ was deposited by electrodeposition to form Si W_12/Ti O₂ composite nanotubes,and then Pb S quantum dots were adsorbed on Si W_12/Ti O₂ by SILAR method,which form Pb S/Si W₁₂/Ti O₂composite nanotubes.The composite nanotubes were characterized by SEM,XRD,UV-Vi and IR.The investigation of the photovoltaic performance of the Pb S/Si W₁₂/Ti O₂（η/%=0.57）demonstrated showed higher photoelectric conversion efficiency than pure Ti O₂（η/%=0.01）.After doping Pb S and Si W₁₂,the electron transport efficiency increases and the recombination rate of electron and hole decreases.To further improve the photoelectric performance of QDSSCs,Ti O₂ nanotubes were sensitized with Cd Se/Cd S co-quantum dots with polyoxometalates.The co-sensitization of Cd S and Cd Se quantum dots is utilized to improve the electron injection rate and broaden the spectrum absorption range,and the polyoxometalate is used as an electron acceptor to reduce the electron-hole recombination of Cd S and Cd Se.Uv-vis,EIS and J-V tests showed that Cd Se/Cd S/Si W₁₂/Ti O₂ had a wider light absorption range,lower electron-hole recombination rate and higher photoelectric conversion efficiency compared with Ti O₂,Si W_12/Ti O₂ and Cd S/Si W₁₂/Ti O₂,the short-circuit current is 3.42 m A/cm²,the open-circuit voltage is 0.32V,and the photoelectric conversion efficiency is 0.61%.Nonce,the application of perovskite in solar cells has attracted unprecedented attention,but the introduction of polyoxometalates in perovskite is rarely studied.Inorganic perovskite Cs Pb I₃ has high light absorption coefficient,suitable band gap width and favourable stability.Therefore,Cs Pb I₃ and polyoxometalates were used as photosensitizers to modify Ti O₂ nanotubes.Firstly,Cs Pb I₃ quantum dots were synthesized by thermal injection,and then Cs Pb I₃ quantum dots were adsorbed onto Si W₁₂/Ti O₂composite nanotubes by chemical bath deposition method.Through the modification of Cs Pb I₃,the spectral response range was broadened（300-700 nm）,and the photoelectric conversion efficiency reached 0.36%,1.4 times higher than that of Si W₁₂/TiO₂.