Enhance the Performance of CZTSSe Solar Cells Through Inhibiting the Cu2+, Tu, and (─COOH) Association Reaction

Abstract The Sol‐gel precursor solution reaction mechanism has a significant impact on the Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cells. It is discovered that in the Cu 2 ZnSnS 4 (CZTS) precursor solution (CZTS‐PS) in the preparation, there is an association reaction among Cu 2+ , thiourea (Tu), and carboxyl (‐COOH), which is an important reason for the undesirable CZTSSe solar cells. The strong association reaction generates excessive Cu 2+ ions, forming the Cu x Se secondary phase on the surface of the CZTSSe absorber. The secondary phase causes a short circuit and deterioration of gadget performance. Following a 6‐h aging period for the CZTS‐PS, the average photoelectric conversion efficiency (PCE) of the device is enhanced to 8.02%, and there is also an improvement in device uniformity, as evidenced by a decrease in the standard deviation to less than 1. To inhibit the association reaction and eliminate the aging time phenomenon, a strategy is developed using hydrochloric acid to regulate the CZTS‐PS environment. This strategy shifts the REDOX reaction in Cu 2+ +Sn 2+ toward the formation of Cu 1+ +Sn 4+ , leading to a decrease in the defect concentrations of V Sn (−/0) and Cu Sn (−/0), which increases the carrier concentration and reduces the impact of band tailing. The average power conversion efficiency (PCE) of the devices improved from 7.45% to 9.26%, the PCE of the best‐performing CZTSSe solar cells increased from 9.25% to 9.83%, and the consistency among the devices is further enhanced, as indicated by a reduction in the standard deviation from 0.98 to 0.44. Ultimately, the device performance of the Cu 2+ +Sn 2+ ‐DMF system improved by 11.01% (without the MgF 2 layer) after optimization. This study serves as a reference for regulating the environment of the CZTS‐PS to further enhance the CZTSSe devices' performance, and the photoelectric conversion efficiency is improved by ≈30%.