Impact of Oxygen Incorporation on Interface Optimization and Defect Suppression for Efficiency Enhancement in Cu2ZnSn(S,Se)4 Solar Cells

Kesterite Cu 2 ZnSn（S,Se） 4 （CZTSSe） solar cells suffer from severe carrier recombination, limiting the photovoltaic performance. Unfavorable energy band alignment at the p-n junction and defective front interface are two main causes. Herein, oxygen incorporation in CZTSSe via absorber air-annealing was developed as a strategy to optimize its surface photoelectric property and reduce the defects. With optimized oxygen incorporation conditions, the carrier separation and collection behavior at the front interface of the device is improved. In particular, it is found that oxygen incorporated absorber exhibits increased band bending, larger depletion region width, and suppressed absorber defects. These indicate the dynamic factors for carrier separation become stronger. Meanwhile, the increased potential difference between grain boundaries and intra grains combined with the decreased concentration of interface deep level defect in the absorber provide a better path for carrier transport. As a consequence, the champion efficiency of CZTSSe solar cells has been improved from 9.74% to 12.04% with significantly improved open-circuit voltage after optimized air-annealing condition. This work provides a new insight for interface engineering to improve the photoelectric conversion efficiency of CZTSSe devices.