It is very important to understand why a small amount of alkali metal doping in Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells can improve the conversion efficiency. In this work, Na-doped CZTSSe is prepared by a simple solution method, and then the effects on the surface properties of the absorber layer, the buffer layer growth, and the modifications of the solar cell performance induced by the Na doping are studied. The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping. In addition, the contact angle of the surface increases because of Na doping. As a consequence, the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased. The difference of quasi-Fermi levels (E_Fn – E_Fp) increases with a small amount of Na doping in the CZTSSe solar cell, so that open circuit voltage (V_OC) increased significantly. This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.

了解为什么在Cu ₂ ZnSn（S，Se）₄（CZTSSe）太阳能电池中少量碱金属掺杂可以提高转换效率非常重要。在这项工作中，通过简单的溶液法制备了掺Na的CZTSSe，然后研究了Na掺杂对吸收层表面性能，缓冲层生长以及太阳能电池性能的影响。由于Na的掺杂，吸收层的表面具有更多的铜耗尽和更少的粗糙度。另外，由于Na掺杂，表面的接触角增加。结果，CdS缓冲层的厚度显着减小，并且CdS缓冲层中的光学损耗减小。准费米能级（E _Fn– E _Fp）随CZTSSe太阳能电池中少量的Na掺杂而增加，因此开路电压（V _OC）显着增加。这项工作通过基于解决方案的方法为Na掺杂对CZTSSe的影响提供了新的见解，并提供了对Na掺杂CZTSSe薄膜太阳能电池效率提高的起源的更深入了解。