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

Modifying the back contact interface plays a key role in improving the efficiency of Cu2ZnSn(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 Mg2+ 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.