Improving the quality of back contact interface in Cu₂ZnSn(S,Se)₄ solar cells by inserting a thin Mg(OH)₂ intermediate layer

Abstract Modifying the back contact interface plays a key role in improving the efficiency of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. Aiming at the phase decomposition and carrier recombination issues in the CZTSSe/Mo back contact interface, an ultra-thin Mg(OH) 2 intermediate layer was introduced between the Mo substrate and the CZTSSe absorber layer. The Mg(OH) 2 intermediate layer effectively suppressed the interface phase decomposition reactions and inhibited the generation of interface secondary phases. Meanwhile, during the high-temperature selenization process, the Mg 2+ doped into CZTSSe at the back contact interface, reducing the defects and band offset at the CZTSSe/Mo interface. The performance of the device was improved, with a significant increase in efficiency compared to the control device. This work highlights the modification effect of Mg(OH) 2 for improving back contact and also provides an easy-handling method to achieve high-performance CZTSSe solar cells.