Device Postannealing with Superficially Ag‐Modified Absorber for High‐Efficiency Cd‐Free Cu 2 ZnSnS 4 Solar Cells

Cation substitution is a promising research direction for further improving the device performance of Cu 2 ZnSnS 4 (CZTS) solar cells by mitigating recombination loss at deep‐level defects. Here, a superficial Ag 2 ZnSnS 4 (AZTS) modification process on presulfurized cosputtered CZTS precursor is employed for fabricating a CZTS absorber film of layer‐spanning grains with reduced interfacial Cu Zn tail states of deeper level and increased minority carrier lifetime. Results show that the open‐circuit voltage and short‐circuit current density of the CZTS device are increased after the modification, though the FF is decreased due to a reduced carrier density of CZTS and a degraded junction electric field. With a postdevice air annealing process, the poor junction quality of the AZTS‐modified CZTS can be recovered without introduction of extra interfacial deep‐level defects. An encouraging efficiency of 10.50% with a remarkably high short‐circuit current density of 22.9 mA cm −2 is achieved with antireflecting coating. This study demonstrates a unique method for reducing interfacial and bulk recombination loss while improving the junction quality of CZTS, which can help in designing strategies for improving the V OC and FF of CZTS.