Defect Engineering in Earth‐Abundant Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub> Photovoltaic Materials via Ga<sup>3+</sup>‐Doping for over 12% Efficient Solar Cells
Yachao Du, Shanshan Wang, Qingwen Tian, Yuechao Zhao, Xiaohuan Chang, Haiqin Xiao, Yueqing Deng, Shiyou Chen, Sixin Wu, Shengzhong Liu
Abstract
Abstract The efficiency of earth‐abundant Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells is considerably lower than the Shockley–Queisser limit. One of the main reasons for this is the presence of deleterious cation disordering caused by Sn Zn antisite and 2Cu Zn +Sn Zn defect clusters, resulting in a short minority carrier lifetime and significant band tailing, leading to a large open‐circuit voltage deficit, and hence, low efficiency. In this study, Ga‐doping is used to increase the CZTSSe solar cell efficiency to as high as 12.3%, one of the highest for this type of cells. First‐principles calculations show that the preference of Ga 3+ occupying Zn and Sn sites has a benign effect on suppressing the formation of the Sn Zn deep donor defects by upwardly shifting the Fermi level, which is further confirmed by deep‐level transient spectroscopy characterization. Besides, the Ga dopants can also form defect‐dopant clusters, such as Ga Zn +Cu Zn and Ga Zn +Ga Sn , which also have positive effects on suppressing the band‐tailing states. The defect engineering via Ga 3+ ‐doping may suppress the band‐tailing defect with a decreased Urbach energy, elevate the minority carrier lifetime, and in the end, enhance the V OC from 473 to 515 mV. These results provide a new route to further increase CZTSSe‐based solar cell efficiency by defect engineering.