Multifunctional Optimization Strategy for High-Efficiency Kesterite Cu₂ZnSn(S, Se)₄ Solar Cell via Cr Doping

Cation doping strategies have shown the significant potential in enhancing the open-circuit voltage (V_OC) of kesterite solar cells. Herein, the extra chromium (Cr) doping is used to improve the efficiency of CZTSSe solar cells by 49%. The introduction of Cr³⁺ ions into the CZTSSe films can promote the cation diffusion, distributing uniformly throughout the film, and help the disappearance of voids at the back interface, increasing its ohmic contact with Mo electrode. The introduction of Cr³⁺ ions can limit to generate the deep level defects by forming Cr_Zn defects, help to improve the electrical properties of the CZTSSe film, and achieve the improved energy (E_U) band structure of heterojunction. The introduction of Cr³⁺ ions can promote the low-energy photon transitions and transport of more photogenerated carriers. These optimized properties of CZTSSe films ensure that the photoelectric conversion efficiency of the device is improved from 8.48% to 12.61%. This work confirms the good role of Cr³⁺ ions doping in optimizing the performance of CZTSSe solar cells, and provides its influence mechanisms of high-performance kesterite photovoltaics.