Synergistic effects of Li&Na co-doping enabling flexible Cu2ZnSn(S,Se)4 solar cells with over 10% certified efficiency

Abstract Double ion doping is an effective strategy for efficiently flexible Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells, simultaneously relieving the adverse effects of various defects. Here, a Li&Na co-doped strategy is applied to synergistically inhibit the detrimental bulk defects in CZTSSe absorbers and improve the devices performances. A power conversion efficiency ( PCE ) of 10.53% with certified 10.12% for the flexible CZTSSe solar cell has been achieved. The space charge limited current (SCLC) and temperature-dependent conductivity (TDC) characterizations show that Li incorporation passivates harmful Cu Zn anti-site defects and Na incorporation increases beneficial defects in the CZTSSe films. Synergistic effects of Li and Na incorporations increase carrier concentration and reduce the interfacial defects, thereby enhancing V oc by 19.76% compared with the undoped device. In addition, profiting from the high-performance small-area (0.205 cm 2 ) devices, we achieve a large-area (2.38 cm 2 ) flexible CZTSSe device with a 9.41% PCE . The co-doping investigation to alter the characteristics of detrimental defects provides a new perspective for efficiently flexible CZTSSe solar cells.