Boosting the efficiency of kesterite Cu2ZnSnS4 solar cells by optimizing the heterojunction interface quality

Heterojunction interface of the Cu$_{\mathbf {2}}$ZnSnS$_{\mathbf {4}}$ (CZTS) solar cells is one the critical factors for performance loss, especially when applying Zn-based alternative buffer replacing CdS. In this work, the CZTS/ZnCdS interface quality is optimized by applying ammonia as complexing agent in the precursor solution of the SILAR process for ZnCdS deposition. Excess oxide and hydroxide impurities formed at the interface are limited to a low level, which reduces the related electronic defects in the depletion region and alleviates the metastability behavior caused by the Zn(OH)$_{\mathbf {2}}$. The application of ammonia also enables the control of reaction mechanism, improving the epitaxial growth, thereby reducing the heterojunction interface recombination. Finally, efficiency of up to 10% is achieved by modifying the interface structure thanks to the chemistry method.