Studies On ZnO/ZnS/CdS Nanotubes Quantum Dot Solar Cells

Dye-sensitized solar cells(DSSC)based on the photosensitization of an oxide semiconductor(such as TiO2,SnO2,ZnO et.al.)by adsorbed organic dyes have recently emerged as the most promising candidate systems.At present,despite the success of DSSC using ruthenium dyes,researching alternative sensitizers is still needed in order to improve the performance and overcome the shortcomings of its easy degradation and short life for dye molecules.So low band-gap semiconductors such as CdS,PbS,and CdSe have been explored to serve as photosensitizers because of their advantages over dyes.Mesoporous semiconductor nanoparticles film is usually used to be anode,but the photogenerated carriers are easily captured by the isolated nanoparticles,defects or surface states and so on.This will reduces the photonic current density and restricts the efficiency of the solar cell.One of the effective ways to solve the photonics recombination is to use one-dimensional nano-array thin film instead of nano-particles film.Consequently,the electrons can reach the substrate directly and-reduce the recombination,leading to high efficient of the solar cell.Although the band gap of ZnO is as similar as TiO2,ZnO has a much higher electron mobility compared with TiO2.Besides,ZnO nanostructures with various morphologies can be fabricated easily.As a result,ZnO has attracted much attentions on the DSSC.Although ZnO-based quantum dot solar cells(QDSSC)have made significant progress,the photoelectric conversion efficiency is still low.It has been reported recently that introduction of the ZnS buffer layer between the ZnO and quantum dot layer could improve efficiency of the solar cell because of the significant reduction of the recombination of photo-induced electrons and vacancy.In this presentation,ZnO/ZnS nanotubes were prepared by etching the ZnO nanorods with thioacetamide(TAA)and used to load CdS quantum dots to study the properties of photoanodes for QDSSC.The main works are as following.1.The ZnO/ZnS/CdS nanorod arrays were successfully prepared on FTO glass and its corresponding QDSSC exhibited a relatively high efficiency.First,ZnO nanorods film were fabricated on the surface of the FTO conductive glass,Then the one-dimensional ZnO/ZnS nanorods core-shell structure was developed by coating ZnS on the surface of ZnO nanorods through liquid-phase deposition method.Finally,ZnO/ZnS/CdS nanorod arrays were successfully obtained by loading CdS quantum dots on the surface of the ZnO/ZnS nanorods.The crytal and morphological structure of the films were studied via X-ray diffraction,scanning electron microscopy and transmission electron microscopy.Amazing,the photoelectric conversion efficiency of QDSSC based on ZnO/ZnS/CdS nanorod array was 0.668%,which is better than that of ZnO/CdS nanorod array.The improvement of the efficiency is attributed to the introduction of ZnS buffer layer,which can tremendously reduce light electronic recombination.2.The ZnO/ZnS/CdS nanotubes on FTO glass were successfully synthesized for the first time in QDSSC field.Firtly,ZnO nanorods were fabricated on the FTO conductive glass.Then they were etched with TAA,which resulted in ZnO/ZnS nanotubes.Finally,the ZnO/ZnS nanotubes were modified using CdS particles by ion exchange method.Surprisingly,the QDSSC based on ZnO/ZnS/CdS nanotudes achieved a photoelectric conversion efficiency of 0.820%.This method is simple and easy to operate,and can provide new ideas for the future research on quantum solar cells.In order to explore the best method for loading CdS on the surface of ZnO/ZnS nanotube arrays,we also compared the successive ionic layer absorption and reaction(SILAR)method with the ion exchange method and investigated effect of the different cycle of SILAR for loading CdS on the performance of QDSSC.