Morphological control of Cu2ZnSn(S,Se)(4) absorber films via inverted annealing for high-performance solar cells

Abstract

In recent years, the method of forming Cu2ZnSn(S,Se)(4) (CZTSSe) by heating precursors has been widely used, but the chalcogen vapor conditions and the placement of the sample have not been disclosed completely. Here, we demonstrate a novel inverted annealing process that enables the reaction between the chalcogen vapor and precursors to remain constant. As a result, we obtained CZTSSe absorber films with an improved morphology and a uniformly distributed elemental composition. The inverted annealed samples showed less variation in the S and Se content as well as in the statistical analysis of the device performance compared with those prepared via the original annealing process. These variations in the S and Se content were confirmed several times through X-ray diffraction, energy-dispersive X-ray, and external quantum efficiency analysis. A pn-junction analysis using a Mott-Schottky plot was also conducted. We anticipate that the inverted annealing process will become widely used as it is easily applicable and effective in improving the morphology of CZTSSe absorber films.