Synergistic Crystallization Modulation and Defects Passivation in Kesterite via Anion‐Coordinate Precursor Engineering for Efficient Solar Cells

Abstract It has been validated that enhancing crystallinity and passivating the deep‐level defect are critical for improving the device performance of kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. Coordination chemistry interactions within the Cu‐Zn‐Sn‐S precursor solution play a crucial role in the management of structural defects and the crystallization kinetics of CZTSSe thin films. Therefore, regulating the coordination environment of anion and cation in the precursor solution to control the formation process of precursor films is a major challenge at present. Herein, a synergetic crystallization modulation and defect passivation method is developed using P₂S₅ as an additive in the CZTS precursor solution to optimize the coordination structure and improve the crystallization process. The alignment of theoretical assessments with experimental observations confirms the ability of the P₂S₅ molecule to coordinate with the metal cation sites of CZTS precursor films, especially more liable to the Zn²⁺, effectively passivating the Zn‐related defects, thereby significantly reducing the defect density in CZTSSe absorbers. As a result, the device with a power conversion efficiency of 14.36% has been achieved. This work provides an unprecedented strategy for fabricating high‐quality thin films by anion‐coordinate regulation and a novel route for realizing efficient CZTSSe solar cells.