A Thin In2S3 Interfacial Layer for Reducing Defects and Roughness of Cu2ZnSn(S,Se)4 Thin‐Film Solar Cells

Cu2 ZnSn(S,Se)4 (CZTSSe) has generated considerable research interest owing to its composition of abundant elements and excellent light-absorption properties. However, CZTSSe thin-film solar cells suffer from a considerable deficit in the open-circuit voltage (VOC ), which is mainly due to the severe interfacial recombination induced by the rough surface of CZTSSe and numerous physical defects. In this study, to improve the morphology and reduce the interfacial recombination, an In2 S3 passivation layer was introduced between the CZTSSe and CdS layers via a chemical bath deposition process, and the effects of the In2 S3 layer on the device performance were systematically examined by performing various electrodynamic analyses. The CZTSSe solar cells with thin In2 S3 layers exhibited impressive increases in VOC and conversion efficiency (from 7.33 to 9.24 %), due to the suppression of physical defects and the refined surface morphology resulting from filling the voids and pinholes. In addition, the nanoscale roughness of the In2 S3 /CZTSSe surface increased the number of nucleation sites for the CdS nuclei, which may reduce the activation energy of the heterogeneous nucleation. The presence of In2 S3 layer resulted in uniform growth of CdS without macroscopic CdS agglomerates (i. e., reduced roughness of full devices), which improved the quality of the interface. These findings confirmed that the reduction of physical defects and the improved deposition of the CdS layer enabled by the added In2 S3 passivation layer improved the device performance.