Pre-deposition of CdS layers to improve the diode quality of CZTSSe solar cells

Abstract

The CdS layers are vital for diode quality of cell devices, which have great influences on high-performance CZTSSe solar cells. Optimizing the deposition processes of CdS layers are necessary to improve the diode quality and device efficiency. In this work, CZTSSe solar cells were fabricated without and with pre-deposited CdS layers, which are referred to as one-step and two-step processes, respectively. Then the performances of the CZTSSe solar cells were comparatively studied. Comparing with one-step processes, the efficiency of the solar cell by two-step processes improves from 7.24% to 9.45%. The efficiency improvement is mainly due to the gain of fill factor (FF) from 60.3% to 73.1%. Although the cell devices by different CdS processes have similar levels of interface recombination deduced from the activation energy (Ea), the temperature-dependent ideality factor A and shunt resistance (Rsh) indicate that the device fabricated by two-step possess higher diode quality and lower leakage current, which results in the increase of FF and efficiency. The optimization of CdS layer preparation is an effective approach to improve the efficiencies of solar cells.