Synthesis And Photoelectric Properties Investigation Of Cu₂ZnSnS（Se）₄and CdIn₂S₄Nanostructures

Solar energy is considered to be the most economic and effective among allavailable renewable energy resources. In the solar energy research field, synthesis ofnovel PV materials with simple method is an important research direction. Recently,chalcopyrite-type semiconductors like Cu（In,Ga）Se2or Cu（In,Ga）S2have verybeneficial properties for photo-voltaic applications. Obtained efficiencies areremarkably high, up to nearly20%; however, gallium and indium used for thepreparation of the active layer are very rare and expensive elements. This could leadto a shortage in the supply of these elements and would inhibit a cost-effectivelarge-scaleproduction.A quaternary semiconductor of Cu₂ZnSnS（Se）₄, which is a direct band gapsemiconductor having a high absorption coefficient of the order of104cm-1, has beenregarded as one of most promising materials for light-absorbing materials in solarcells because of its content of only low-toxicity elements that are abundant in theearth crust. Recently, Cu2ZnSn（Se）S4thin films can be prepared using variousmethods, such as atom beam sputtering, RF magnetron sputtering, thermalevaporation, pulsed laser deposition, etc. However, these methods have somedrawbacks such as expensive precursors, complicated apparatus and even some toxicbyproducts evolved during their synthesis. In this thesis, we synthesizedCu2ZnSn（Se）S4and CdIn₂S₄nanostructures via a simple solvothermal route and investigated their photoelectric properties. The main content and innovation of thisthesis are listed as following:（1） Pure Cu₂ZnSnS₄in a hollow sphere morphology has been successfullysynthesized in a PEG-assisted solvothermal reaction with N, N-dimethylformamide asthe solvent. The extensive investigations demonstrated that the PEG plays animportant role in the formation of the hollow spheres.（2） The growth mechanism for the hollow sphere-like particles has beendiscussed.（3）Cu₂ZnSnSe₄particles with flowerlike morphology have been successfullysynthesized in a solvothermal reaction with ethylenediamine as the reaction solvent.Stannite Cu₂ZnSnSe₄with a near stoichiometry composition synthesized bysolvothermal process. A possible growth process of the films was also proposed.（4） The Cu₂ZnSnS₄thin films have been deposited onto FTO glass substrate by asolvothermal method for the first time. These as-deposited films were annealed atdifferent temperatures from250°C to550°C. The influence of the annealingtemperature on the structure, morphology, and composition of the films has beenstudied. The photelectrochemical measurement with CZTS thin films shows that filmsare photoactive which proves itself to be a promising candidate for cost-effective,high efficiency solar cells in future.（5） For the first time, arrays of Cu₂ZnSnSe₄nanotubes were directly grown onfluorine-doped tin oxide glass substrate by using ZnO nanorods as sacrificialtemplates. The solubility product constant （Ksp） of ZnO is larger than those of ZnSeand CuSe. This implies that the arrays of ZnO nanorods can be used as sacrificialtemplates to synthesize more stable ZnSe by anion exchange and further convert intoCuSe by cation exchange to obtain ZnO/CuSe nanocables. Arrays of CZTSe naotubescan be prepared by using the ZnO/CuSe nanocables as self-sacrificial templates toreact with Zn²⁺and Sn2+via a polyol reduction process. The ZnO cores are slowlydissolved by the H⁺ions produced in the reaction.（6） The length and diameter of the CZTSe nanotubes can be adjusted by turningthe length of the ZnO nanorods. The effect of the length on the performance of the photoelectrochemical cells was also investigated. We found the CZTSe nanotubeswith the length of2μm showed the best performance of photoelectrochemical cells.（7） CdIn₂S₄films composed of nanosheets have been directly deposited onfluorine-doped tin oxide substrates using a simple hydrothermal method. TheL-cysteine acting as sulfur source was found to play an important role in theformation of the final films. A possible growth mechanism for the formation CdIn₂S₄films on FTO substrates has been proposed. It was found that the formation ofuniform CdIn₂S₄films attached the FTO substrates underwent the following steps:1)piranha treatment of FTO substrate;2) formation of hetero-nucleation sites on thesubstrate surface;3) growth of CdIn₂S₄film from the nucleation sites.（8） From the results of the photoelectronchemical properties studies, thephotoelectric conversion efficiency of0.162%was obtained under100mW cm-2illumination.