Rapid Grain Growth to Attain over 13% Certified Flexible CZTSSe Solar Cell

A high-quality absorber layer is crucial for highly efficient Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. However, current research on absorber layer is mainly focused on the high-temperature selenization process. Herein, a rapid crystal growth is achieved via regulating the pre-annealing temperature. Lower pre-annealing temperature improves the microstructure of the precursor, which not only facilitates the penetration of Se but also possibly exerts the grain growth-promoting effect during selenization from Ag, thereby leading to improvement in absorber layer quality. Thus, the carrier separation and transport efficiency at grain boundaries are significantly enhanced, the bulk and interface defects are reduced, and the carrier recombination of a device is effectively suppressed. Finally, a flexible CZTSSe solar cell with a certified efficiency of 13.22% (aperture area) is obtained. This work reveals the impact of the pre-annealing process on crystal growth and puts forward an effective strategy to improve the quality of kesterite film.