Formation of Alloyed Cu₂CoZn_1-Sn(S,Se)₄ Absorption Layer and Its Application in Solar Cells

Partial substitution of cations is crucial for suppressing harmful defects in Cu₂ZnSn(S,Se)₄ thin-film solar cells. In this study, based on the mixed n-butylammonium and butyrate solution system, the alloyed Cu₂CoZn_1-Sn(S,Se)₄ phase can be prepared by substituting Zn²⁺ with Co²⁺, which can suppress harmful defects and optimize the crystallinity of the Cu₂ZnSn(S,Se)₄ absorption layer, and improve the photoelectric conversion efficiency (PCE) of devices. By systematic investigation of the impact of Co content on the performance of devices, the optimal substitution amount of Zn²⁺ with Co²⁺ is 0.05. At this time, PCE, the open-circuit voltage (V_OC), current density (J_SC), and fill factor (FF) of the devices can reach 9.0%, 416 mV, 33.87 mA/cm², and 64%, respectively. It is the first time that the replacement of Zn²⁺ with Co²⁺ is applied to optimize PCE of CZTSSe solar cells. The excellent results also demonstrate that the substitution of Zn²⁺ with Co²⁺ can become a new approach for further performance optimization of Cu₂ZnSn(S,Se)₄ solar cells.