†imec-partner in Solliance, Kapeldreef 75, 3001 Leuven, Belgium.
‡Department of Electrical Engineering (ESAT), KU Leuven, Kasteelpark Arenberg 10, 3001 Heverlee, Belgium.
ACS Appl Mater Interfaces. 2015 Jul 15;7(27):14690-8. doi: 10.1021/acsami.5b02122. Epub 2015 Jul 6.
The removal of secondary phases from the surface of the kesterite crystals is one of the major challenges to improve the performances of Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells. In this contribution, the KCN/KOH chemical etching approach, originally developed for the removal of CuxSe phases in Cu(In,Ga)(S,Se)2 thin films, is applied to CZTSe absorbers exhibiting various chemical compositions. Two distinct electrical behaviors were observed on CZTSe/CdS solar cells after treatment: (i) the improvement of the fill factor (FF) after 30 s of etching for the CZTSe absorbers showing initially a distortion of the electrical characteristic; (ii) the progressive degradation of the FF after long treatment time for all Cu-poor CZTSe solar cell samples. The first effect can be attributed to the action of KCN on the absorber, that is found to clean the absorber free surface from most of the secondary phases surrounding the kesterite grains (e.g., Se0, CuxSe, SnSex, SnO2, Cu2SnSe3 phases, excepting the ZnSe-based phases). The second observation was identified as a consequence of the preferential etching of Se, Sn, and Zn from the CZTSe surface by the KOH solution, combined with the modification of the alkali content of the absorber. The formation of a Cu-rich shell at the absorber/buffer layer interface, leading to the increase of the recombination rate at the interface, and the increase in the doping of the absorber layer after etching are found to be at the origin of the deterioration of the FF of the solar cells.
从黄铜矿晶体表面去除次生相是提高 Cu2ZnSn(S,Se)4 (CZTSSe) 薄膜太阳能电池性能的主要挑战之一。在本研究中，最初开发用于去除 Cu(In,Ga)(S,Se)2 薄膜中 CuxSe 相的 KCN/KOH 化学刻蚀方法被应用于具有不同化学组成的 CZTSe 吸收体。在处理后，CZTSe/CdS 太阳能电池表现出两种截然不同的电性能：(i) 对于最初电特性发生扭曲的 CZTSe 吸收体，在蚀刻 30 秒后填充因子 (FF) 得到改善；(ii) 对于所有 Cu 贫化的 CZTSe 太阳能电池样品，在长时间处理后 FF 逐渐恶化。第一种效应可以归因于 KCN 对吸收体的作用，发现 KCN 可以清除吸收体自由表面上大多数围绕黄铜矿晶粒的次生相（例如 Se0、CuxSe、SnSex、SnO2、Cu2SnSe3 相，除了 ZnSe 基相）。第二种观察结果被认为是 KOH 溶液优先从 CZTSe 表面刻蚀 Se、Sn 和 Zn 的结果，同时吸收体的碱含量发生改变。在吸收体/缓冲层界面处形成富 Cu 壳，导致界面处复合速率增加，以及蚀刻后吸收体层掺杂增加，这被认为是太阳能电池 FF 恶化的原因。
