Crown Ether-Assisted Colloidal ZnO Window Layer Engineering for Efficient Kesterite (Ag,Cu)₂ZnSn(S,Se)₄ Solar Cells

The nature of interfaces between each functional layer of Cu 2 ZnSnS x Se 4– x (CZTSSe) solar cells is the key issue impacting cell performance, typically its influence on carrier recombination and charge transportation. The routine magnetron sputtering method for the ZnO/ITO layers can destroy ordered lattices due to the continuous bombardment of the CZTSSe/CdS heterojunction region. In this work, a sol–gel solution-processed ZnO layer (ZnO-SG) is incorporated to construct a nondestructive heterojunction interface, and 18-crown-6-ether (18C6) is used to further modify this ZnO-SG window layer for better performance. Our investigation reveals that noncovalent interaction between 18C6 and ethanolamine from the ZnO-SG not only reduces defects from the ZnO layer itself but also modulates the energy band position for better band alignment to facilitate carrier transportation. Finally, based on our 18C6-modified ZnO-SG, a total-area 14.06% efficiency and 13.77% certified efficiency have been achieved.