Effects of bending stress on structural and electrical properties of flexible CZTSSe thin film solar cells

The impact of bending stress on the structural and electrical properties of Cu2ZnSn(S,Se)4 (CZTSSe) thin films was studied in this work. Bending stress caused macroscopic separation of CZTSSe grains and microscopic expansion of its lattice. The former resulted in the formation of defects and defect clusters on the grain surface, while the latter induced tensile inner stress within the film. After bending, the nanoscale electric fields near the grain boundaries changed to a dip-type structure, indicating an accumulation of negative charges. Based on changes in stress and potential, we inferred that these negative charges were primarily ZnSn defects. The performance of flexible CZTSSe devices deteriorated due to the combined effects of structural and electrical changes.