Defect Control for High‐Efficiency Cu2ZnSn(S,Se)4 Solar Cells by Atomic Layer Deposition of Al2O3 on Precursor Film

Cu 2 ZnSn(S,Se) 4 are emerging as promising photovoltaic materials due to their outstanding photoelectrical performances, benign grain boundaries, and Earth‐abundant constituent elements. However, there are largely distributed cation‐disordering defects and defect clusters, which lead to an increase in recombination and a large open‐circuit voltage deficit and thus deteriorate device performance. Herein, defect control for a high‐efficiency Cu 2 ZnSn(S,Se) 4 solar cell by atomic layer deposition of aluminum oxide (ALD‐Al 2 O 3 ) on the precursor film is reporter. Cu Zn defects and Sn‐related deep defects are largely suppressed because of the decrease in Sn 2+ and the increase in Sn 4+ in the film by ALD‐Al 2 O 3 on the precursor are found, and the crystallinity of absorber layer is improved from a double‐layer structure to a completely single‐layer structure. Furthermore, the carrier lifetime and recombination in the bulk and interface are significantly improved for devices with ultrathin Al 2 O 3 . Using this approach, the conversion efficiency increases from 8.8% to 11.0% and the open‐circuit voltage deficit decreases from 0.621 to 0.577 V. Herein, a deep understanding of the relationship between Al 2 O 3 incorporation and high‐efficiency Cu 2 ZnSn(S,Se) 4 devices and a new direction for controlling defects to further improve the performance of kesterite solar cells are provided.