Effect of Cu–Sn–Se Liquid Phase on Grain Growth and Efficiency of CZTSSe Solar Cells

摘要

Herein, a liquid-assisted grain growth (LGG) mechanism for a vacuum-processed Cu2ZnSn(S1-xSex)(4) (CZTSSe) absorber that is enabled by the presence of a liquid phase containing predominantly Cu, Sn, and Se (L-CTSe) is suggested to explain the large grain size of up to approximate to 6 mu m obtained at low temperatures, such as 480 degrees C. In this system, LGG plays a key role in achieving a large grain CZTSSe absorber, but the residual L-CTSe, a key factor in LGG, deteriorates the device performance. L-CTSe residue can possibly remain when using metal precursors for reasons such as local composition nonuniformity due to the agglomeration of Cu-Sn alloys, uncontrolled Zn volatilization. It is expected that CZTSSe cells with L-CTSe residues have lower efficiency and fill factor than CZTSSe cells without L-CTSe due to the role of L-CTSe as a shunt path and compositional misfit. These tendencies are observed in the statistical results. Thus, when synthesizing CZTSSe using a metal precursor in a two-step process, it is considered important to design the precursors to remove unwanted L-CTSe residues and optimization of composition.