Research On Properties Of Novel Method Based CulnSe₂and Cu₂ZnSn（Se,S）₄Thin Films For Solar Cells Application

CuInSe2(CISe) and Cu2ZnSn(Se,S)4(CZTSe/S) based thin film solar cells have been considered the most promising solar cells due to respectable conversion efficiency and their outdoor stability. Most high-efficiency CISe PV absorption materials are deposited via vacuum-based deposition processes (e.g., sputtering or evaporation). However, vacuum-based deposition processes are complex and expensive. To eliminate this demanding tolerance requirement, the simple and low-cost techniques based on non-vacuum deposition of CISe absorption layer have been researched. On the other hand, CISe contains expensive materials Indium, which is a problem in mass production. CZTSe/S thin films have attracted significant attention as a potential alternative to CISe thin films, owing to the similar photoelectric properties as CISe thin films. The oxides based CZTSe/S was also investigated. The thesis mainly includes four parts, as follows:The first part is a low temperature solid state synthesis of oxides for CISe thin films. First, highly monodisperse oxides nanoparticles were synthesized via a low temperature solid state reaction, which is facile and easily scaled up. Second, the oxide particulate precursors were deposited in a thin layer by doctor-blade technique. Finally, the dry layers were sintered into CISe thin films. In order to improve the crystallinity of CISe thin films, the effects of heat treatment in vacuum or Ar atmosphere with elemental selenium vapor on the properties of CISe thin films were also investigated. Selenization under Ar atmosphere led to better crystallinity and an increase in the grain size. Meanwhile, densification studies were performed to improve the morphology of CISe thin films. The preliminary CISe solar cells with Ag/AZO/i-ZnO/CdS/CISe/Mo/Glass structure were fabricated. The solar cell device showed efficiency of3.4%.The second part includes the preparation of CISe thin films with In2O3-free by selenizing pre-annealed Cu-In hydroxide precursors. CISe thin films were prepared from hydroxides instead of oxides, which can avoid the formation of In2O3impure phase. The precursor film based on Cu, In hydroxides was firstly prepared by drop-casting and then sequential pre-annealing and selenization treatments were performed in Ar and Se vapor, respectively. The influence of pre-annealing temperature on the preparation of single phase CISe thin films has been systematically investigated. CISe thin films with smooth surface, dense and In2O3-free can be achieved when pre-annealing was performed at350℃. A Cu-deficient surface layer was found although the bulk composition was Cu-rich. The In-rich surface was benefited for the high efficiency CISe solar cells.The third part is a low-cost non-vacuum process for fabrication of Cu2ZnSnSe4(CZTSe) thin films by direct selenization of oxides nanoparticles. To reduce the cost of solar cell, the CZTSe thin film can be obtained by replacing the expensive element indium in CISe with the low-cost zinc and tin. First, highly monodisperse Cu, Zn, Sn oxides nanoparticles were synthesized via a facile, low temperature solid state route. Second, the CZTSe thin films were deposited via doctor blade from precursor slurry consisting of Cu, Zn, Sn oxides and selenization. We have studied the effects of compact precursor on the structure, morphology and optical property of CZTSe thin film. The near stoichiometric CZTSe thin films with micron-sized grains were obtained in our work. These results provide a novel non-vacuum route for the preparation of CZTSe thin film solar cell.The last part is the preparation of non-toxic Cu2ZnSnS4(CZTS) thin film solar cell from oxides nanoparticles ink. The CZTS thin films were obtained by annealing oxide precursor under sulfur vapor atmosphere. The band gap of CZTS (1.5eV) is more suitable as an absorption material, compared to CZTSe (1.0eV). Generally, the crystallinity of CZTS is poor than that of CZTSe. In order to improve the crystallinity of CZTS thin films, we have made a systematic study on the annealing conditions. Through the introduction of high temperature sulfurization, the CZTS thin film with high quality was obtained. These results laid a solid foundation for the fabrication of high efficient CZTS thin film solar cell.