Band Gap and Defect Engineering for High‐Performance Cadmium‐free Sb2(S,Se)3 Solar Cells and Modules

High‐efficiency antimony selenosulfide (Sb2(S,Se)3) solar cells are often fabricated by hydrothermal deposition and also comprise a CdS buffer layer. Whereas the use of toxic materials such as cadmium compounds should be avoided, both of these issues hinder scaling up to large areas and market access. For this reason, co‐sublimation is studied as a manufacturing process for the active layer as well as the use of Cd‐free buffer layers. To further improve the power conversion efficiency (PCE), a graded bandgap profile is designed for the absorber layer. A V‐shaped graded bandgap in the Sb2(S,Se)3 absorber layer is produced on a TiO2 substrate by co‐sublimation of a controlled varying molar ratio of Sb2Se3 and Sb2S3. Moreover, increasing the Se/S ratio improves the grain size and favorable (hk1) orientations, reduces the detrimental bulk defects in Sb2(S,Se)3 films. Consequently, the optimized Sb2(S,Se)3 solar cells reach a PCE of 9.02%, which is a record value for Cd‐free Sb‐based solar cells. A PCE of 7.15% is further demonstrated for a Sb2(S,Se)3 monolithically interconnected minimodule with an active area of 12.32 cm2. This co‐sublimation graded bandgap technique provides a useful guidance for the optimization of a range of solar cells based on alloy compounds. The V‐shaped graded bandgap Sb2(S,Se)3 absorbers with the reduced shallow and deep defects are prepared by the easily scalable co‐sublimation technique. The optimized Sb2(S,Se)3 solar cells achieve a PCE of 9.02%, which is a record value for Cd‐free Sb‐based solar cells. Furthermore, a PCE of 7.15% is demonstrated for a larger area Sb2(S,Se)3 solar module with an active area of 12.32 cm2.