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 Cu2ZnSn(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 CuZn 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 Voc by 19.76% compared with the undoped device. In addition, profiting from the high-performance small-area (0.205 cm2) devices, we achieve a large-area (2.38 cm2) 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.