Effect of defect on the properties of the CuInSe₂ compound

CuInSe₂ (CISe) is a semiconductor compound used in photovoltaic applications. There are many ways to synthesize CISe, and the different synthesis methods result in CISe compounds with very different properties. The photoelectric conversion efficiency of a single-junction solar cell is predicted by Shockley and Queisser to be as high as 32%; however, the prediction only considers the semiconductor’s bandgap value and the incident solar spectrum. In this study, a nearly cubic CISe supercell is constructed, and the influence of defects under different chemical potentials on the properties, especially the photovoltaic properties, is examined. The results show that p-type CISe is favorable in the stable chemical potential region when defect features are accounted for, but it has a photoelectric conversion efficiency of approximately 15%. The densities of the defects are calculated for the first time, revealing that the deep-level Cu_In defect with a high density could be the limiting factor for efficiency. Notably, there is a narrow chemical potential range that allows a high carrier density and relatively low defect density. The efficiency of p-type CISe can reach 22.77% within this chemical potential with a deep-level defect density, n₀, and p₀ carrier densities of 1.119 × 10¹⁶, 1.295 × 10², and 9.827 × 10¹⁷ cm^− 3, respectively. These findings help clarify defect-induced efficiency loss, which is crucial for improving the large-scale low-cost fabrication of high-efficiency solar cells with intrinsically high defect densities.