基于(Zn,Mg)O缓冲层的宽带隙Cu2ZnSn(S,Se)4太阳电池异质结界面匹配

Recently, Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells have attracted considerable attention, as one of the most promising PV technologies which take advantages of low-cost, eco-friendliness, and large efficiency potential. The large band gap CZTSSe solar cells have larger potential owing to the ideal band gap that perfectly matches with the solar spectrum. However, suffered from the hetero-junction interface mismatch with conventional CdS buffer layer, the large band gap CZTSSe solar cells encounter large open circuit voltage deficit and poor power conversion efficiency. In this proposal, we will focus on the hetero-junction interface of the large band gap CZTSSe solar cells. (Zn,Mg)O films deposited by electron-beam evaporation will be used as the alternative buffer layers. The band alignment between the CZTSSe and (Zn,Mg)O layers will be improved by fine tuning the conduction band of the (Zn,Mg)O film, and the matching of electronic property for the hetero-junction interface will be improved by a suitable n-type doping for the (Zn,Mg)O layer. In addition, based on the analysis of device simulation and interface characterization, the charge carrier transport mechanism in the junction interface can be elucidated, and the limitation of the open circuit voltage can be overcome, thus facilitating the further development of kesterite solar cells to a more competitive level.

近几年来，铜锌锡硫硒（Cu2ZnSn(S,Se)4，CZTSSe）薄膜太阳电池因其环境友好、低成本、发展潜力大等优势，获得了广泛的关注。其中，宽带隙CZTSSe电池具有与太阳光谱相匹配的理想吸收层带隙，因而具有更大的发展潜力。然而，与传统CdS缓冲层构成的异质结界面失配成为严重制约宽带隙CZTSSe太阳电池开路电压和光电转换效率的一个重要因素。本项目围绕宽带隙CZTSSe太阳电池的异质结界面匹配问题展开，采用电子束蒸发法制备新型(Zn,Mg)O缓冲层，通过精确调控(Zn,Mg)O缓冲层的导带位置，实现电池异质结界面的能带匹配；通过 (Zn,Mg)O薄膜的n型掺杂调控，实现电池异质结界面的电学性能匹配。结合理论模拟和异质结界面分析表征，阐明CZTSSe太阳电池异质结界面的载流子输运机制，突破开路电压限制，推动CZTSSe薄膜太阳电池的发展。

本项目主要围绕铜锌锡硫硒材料的缺陷调控和异质结界面优化等方向展开，取得了一系列系统性成果，主要研究内容及成果包括：通过改善材料生长过程中的元素互扩散过程改善吸收层材料背面电势分布，通过改善铜锌锡硫硒半导体材料生长过程中局部化学环境，有效抑制深能级本征缺陷和高浓度带尾态的形式，并实现了12.5%的铜锌锡硒太阳电池新世界记录，获得第三方权威机构认证；通过优化锌锡氧、锌镁氧等缓冲材料的生长工艺和界面化学环境，优化了宽带隙铜锌锡硫硒太阳电池异质结能带匹配，显著提高开路电压和电池效率；结合深入实验测试分析和器件物理理论推导，揭示限制宽带隙铜锌锡硫硒薄膜太阳电池开路电压和效率损失更主要的机制，即高载流子浓度与高受主型界面缺陷浓度耦合引起的严重界面复合，为进一步提高铜锌锡硫硒太阳电池指明方向。