Defect regulation enhances the efficiency of Cu₂ZnSnS₄ solar cells by solution engineering

The preparation of Cu₂ZnSnS₄ (CZTS) through the solution method demonstrates significant application potential due to its high efficiency, simplicity and low cost. However, CZTS still faces several issues, including poor crystallinity of the absorber and complex intrinsic harmful defects, which severely limit the efficiency of the cell. We have developed a simple and effective method for growing large-grain CZTS thin films and regulating defects. By reducing the concentration of the precursor solution, the crystallinity of the absorber is significantly enhanced, thereby avoiding the occurrence of voids and fine grains, and greatly improving the Fill Factor of the solar cell. Due to the improved crystallinity of the absorber and the shallower energy level of the Cu_Zn defect, the carrier density has significantly increased. Furthermore, the reduction in the density of deep-level defects also decreases non-radiative recombination. Through this method, the photovoltaic performance of CZTS solar cells without extra post-annealing has been significantly improved, achieving a cell efficiency of 7.6 %.