Effects of Back Annealing on the Structural and Electrical Properties of Cu2ZnSnSe4 Thin Films Grown by a Modified Two-Step Process

In this study, we investigate the electrical and structural properties of Cu2ZnSnSe4 (CZTSe) thin films grown by a two-step process. CZTSe precursors are deposited on a Mo-coated soda-lime glass (Mo/SLG) by coevaporation at 150 degrees C. After deposition, the precursors are annealed in different directions under normal pressure by rapid thermal processing (RTP) at 590 degrees C. One precursor is annealed from the top of the precursor (front annealing), and another is annealed from the Mo/SLG side (back annealing). Using a back-annealing RTP of the co-evaporated Cu-Zn-Sn-Se precursor, the efficiency of CZTSe devices is increased by more than 60%. The surface morphology and grain size of the CZTSe thin film is greatly improved after back annealing. In the XRD patterns, the back-annealed CZTSe thin film also shows the improved crystal quality for the (112), (024), and (132) planes. The reverse saturation current density of the back-annealed CZTSe thin film is 10 times smaller than that of the front-annealed thin film. From these results, we find that the back-annealing method can improve the structural and electrical properties of CZTSe thin films.