Study On Selenization And Photoelectric Performance Of Cu₂ZnSn?S,Se?₄ Thin Film

The research in thin film solar cells has been dominated by light absorber materials based on CdTe and Cu(In,Ga)Se2(CIGS) in the last several decades. However, the concerns of environment influence of cadmium and the limited availability of indium in those materials have driven the research towards developing new substitutes consisting of earth abundant, environment benign elements.Chalcogenides compound semiconductor material Cu2ZnSn(S,Se)4(CZTSSe), which is derived from chalcopyrite CIGS material, has attracted considerable interest, because of CZTSSe's earth-abundant and comparable photoelectric performances CIGS and CdTe.So far, many vacuumand non-vacuumtechnologies have been employed toprepare CZTSSe thin films,where the precursor solutionmethod is the most commonly used. This approach offers advantages such as the possibility to use low-cost and high-throughput equipment, low wastage of raw materials, high uniformity of layer properties over large area and especially, the potential deployment of large-scale production with low capital investment.In this thesis, precursor solution method was utilized for preparing CZTSSe thin film.Large-grained CZTSSe thin film without fine-grained layer was obtained via optimizing the condition of selenization(selenization setup, annealing temperature, annealing time, dosage of selenium powder and multiple annealing processes). Surface photovoltage test and resistivity test were adopted to characterize the photoelectric performance of CZTSSe thin films with different crystallization, and the effect of crystallization of absorber layer thin film on the performances of solar cells were investigated. This work mainly carried out following the three aspects:1. Preparation of CZTSSe thin film. The precursor solution containing copper, zinc, tin, sulfur elements was obtained by dissolving Cu2 O, Sn Cl4·5H2O, ZnCl2·2H2O in turn into the solution of1-butyldithiocarbamic(the reaction product of 1-butylamine and carbon disulfide) in turn, in which ethanol act as the solvent. Subsequently, the spin-coating/low temperature pretreatment processes was followd for several times to obtain precursor film. Finally, a high-temperature post-selenization treatment process was employed to recrystallize the precursor film into CZTSSe thin film.2. Preparation of CZTSSe thin film with large grain. we study the fundamental factor that govern the microstructure of large-grained thin films formed by annealing precursor thin film in selenium-containing atmosphere. Sepecially, we systematically optimize the factor of selenization setup,annealing temperature, annealing time, dosage of selenium powder and multiple annealing processes. And the sample was characterized with X-ray diffraction patterns, Raman spectra, scanning electron microscope(SEM), and energy dispersive spectrometer(EDS) and so on. The results show that the pure kesterite CZTSSe thin film with large dense grain was successfully obtained.3.device fabrication and photoelectric performance characterization. Surface photovoltage test and resistivity test were adopted to characterize the photoelectric property of CZTSSe thin film with different crystallization(nanoparticle thin film, bi-layer structure thin film with a large-grained layer on top and a fine-grained layer on the bottom, large-grained thin film). It turned out that the photoelectric transmission performance based on large-grained thin film is superior to that based on nanoparticle thin film and bi-layer structure thin film. Finally, the solar-cell device was fabricated according to the structure of glass/Mo /CZTSSe /CdS /i-ZnO /AZO/Al. The power conversion efficiency was up to 2.13% with a 0.5cm2 active area.Some viewpoints of this thesis provide a gist for the preparation of large-grained CZTSSe thin film. We believe therefore that these pioneering work will provide significant scientific contribution to the further understanding of the thin film solar cells.