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 Cu2ZnSnSxSe4–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.