An efficient Cr-doping strategy to optimize the solution-processed Cu2ZnSn(S,Se)4 solar cells for better optoelectronic performance

Abstract

Owing to open-circuit voltage (VOC) deficits, Cu2ZnSn(S,Se)4 (CZTSSe) alloy film solar cells have limited improvements in device performance. Cation replacement in CZTSSe absorbers is key in studying the enormous potential of kesterite solar cells and thus in developing cost-effective photovoltaic technology. In this study, Cu2CrxZn1−xSn(S,Se)4 (0 ≤ x ≤ 0.2) (CCZTSSe) films were prepared using solution-processing and a two-step annealing technique. The device properties and effects of Cr-doping on the structure, morphology, and optoelectrical performance of the CCZTSSe films were investigated. The results showed that appropriate Cr-doping promotes grain growth, which enables the production of compact CCZTSSe films with larger grain sizes and fewer holes. In addition, the significantly enhanced absorption of the CCZTSSe thin films indicates the presence of intermediate bands (IB) in the band gaps, which promotes the absorption of low-energy photons. Cr-doping can also reduce the CuZn antisite defects. Finally, the efficiency of the CCZTSSe (x = 0.1) device was enhanced from 3.74 % to 5.44 %, and the VOC was boosted from 0.35 V to 0.39 V, compared to the pure CZTSSe (x = 0) device. These findings pave the way for improvements in the efficiency of CZTSSe devices.