A study on Sr-doping strategy to promote growth and suppress defects for enhancing the optoelectronic performance of solution-processed Cu2ZnSn(S,Se)4 solar cells

Enhancing the quality of the absorption layer represents a major approach to improving the optical response and electronic transport characteristics of Cu2ZnSn(S,Se)4(CZTSSe) solar cells. Numerous studies indicate that cation doping is a productive strategy for enhancement of efficiency. In this context, we present a method to enhance the crystallinity of the absorption layer and to passivate deep traps by doping Sr2+ into the absorption layer to partially replace Zn2+. The results demonstrate that Sr doping concentration of 0.10 yields the most significant improvement in film crystallinity. Concurrently, the density of beneficial defect clusters [VCu + ZnCu] increases, while that of harmful defect clusters [2CuZn + SnZn] decreases. At the same time, Sr doping can efficiently alleviate the band tailing phenomenon in the CZTSSe absorber layer and improve the open − circuit voltage (Voc). Upon the execution of the Sr doping strategy, the efficiency of Cu2SrxZn(1-x)Sn(S,Se)4(CSZTSSe)(0 ≤ x ≤ 0.2) solar cells increases from 6.31 % to 8.07 %, with the main contributing factors being the improvements in Voc and Fill Factor (FF). The proposed innovative methodology provides a comprehensive understanding of crystallization processes in kesterite-based solar cell materials, thereby paving the way for optimizing crystallinity and enhancing light-absorbing layer performance.