# Device Postannealing with Superficially Ag‐Modified Absorber for High‐Efficiency Cd‐Free Cu2ZnSnS4 Solar Cells

## TL;DR

Researchers improved the efficiency of CZTS solar cells by modifying the absorber layer with silver and postannealing, reducing defects and boosting performance.

## Contribution

A superficial Ag2ZnSnS4 modification combined with postannealing is introduced to reduce recombination loss and enhance CZTS solar cell efficiency.

## Key findings

- The Ag2ZnSnS4 modification reduces interfacial deep-level defects and increases minority carrier lifetime in CZTS.
- Postannealing recovers junction quality without introducing new defects, achieving 10.50% efficiency with high current density.
- The process suppresses nonradiative recombination and enables Cd-free CZTS solar cells with 10.53% efficiency.

## Abstract

Cation substitution is a promising research direction for further improving the device performance of Cu2ZnSnS4 (CZTS) solar cells by mitigating recombination loss at deep‐level defects. Here, a superficial Ag2ZnSnS4 (AZTS) modification process on presulfurized cosputtered CZTS precursor is employed for fabricating a CZTS absorber film of layer‐spanning grains with reduced interfacial CuZn 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.

A superficial Ag‐modification process using spin‐coated Ag2ZnSnS4 layer on presulfurized CZTS precursor is proposed to improve the surface defect properties. The absorber fabrication process reduces the interfacial nonradiative recombination loss and suppresses the generation of deep defects during device annealing, enabling 10.53% efficient Cd‐free CZTS solar cells.© 2026 WILEY‐VCH GmbH