An ITO-Free Kesterite Solar Cell

Yixiong Ji, Wangxian Chen, Di Yan, James Bullock, Yang Xu, Zhenghua Su, Wentong Yang, Jamie Stuart Laird, Tian Zheng, Na Wu, Wusong Zha, Qun Luo, Chang-Qi Ma, Trevor A. Smith, Fangyang Liu, Paul Mulvaney

Small 20, page 2307242 (2024), https://doi.org/10.1002/smll.202307242

Photovoltaic thin film solar cells based on kesterite Cu2ZnSn(S, Se)4 (CZTSSe) have reached 13.8% sunlight-to-electricity conversion efficiency. However, this efficiency is still far from the Shockley-Queisser radiative limit and is hindered by the significant deficit in open circuit voltage (VOC). The presence of high-density interface states between the absorber layer and buffer or window layer leads to the recombination of photogenerated carriers, thereby reducing effective carrier collection. To tackle this issue, a new window structure ZnO/AgNW/ZnO/AgNW (ZAZA) comprising layers of ZnO and silver nanowires (AgNWs) is proposed. This structure offers a simple and low-damage processing method, resulting in improved optoelectronic properties and junction quality. The ZAZA-based devices exhibit enhanced VOC due to the higher built-in voltage (Vbi) and reduced interface recombination compared to the usual indium tin oxide (ITO) based structures. Additionally, improved carrier collection is demonstrated as a result of the shortened collection paths and the more uniform carrier lifetime distribution. These advances enable the fabrication of the first ITO-free CZTSSe solar cells with over 10% efficiency without an anti-reflective coating.