Efficiency improvement of electrodeposition-processed Cu(In,Ga)Se2 solar cell with widen surface bandgap by spin-coating In2S3 thin film

Abstract

The Cu(In,Ga)Se2 (CIGSe) -based solar cell is a promising candidate in the photovoltaic market due to its excellent performance. It was reported that the surface bandgap of CIGSe is crucial to improve the device properties. However, in the post-selenization process of precursor layers, Ga tends to accumulate at the back contact leading to a narrow surface bandgap. In this work, the surface bandgap of CIGSe film was successfully widened by a spin-coating In2S3 thin film on the CIGSe surface. After annealing treatment of the CIGSe/In2S3 stack, sulfur incorporates into the absorber layer and a Cu-poor surface composition is formed. Thus, a surface inversion of CIGSe from p-type to n-type occurs leading to formation of a buried homojunction. The effect of different In2S3 thicknesses on device performance were investigated. A champion efficiency of 12.88 % for CIGSe solar cell was obtained with 40 nm In2S3 compared to 10.03 % for the reference device without In2S3. However, the performance of CIGSe solar cells were deteriorated with In2S3 film thicknesses over 40 nm. These results demonstrate that a suitable In2S3 film thickness is significant to increase the surface bandgap and promote the efficiency.