Band Gap and Defect Engineering for High-Performance Cadmium-free Sb_2(S,Se)_3 Solar Cells and Modules

摘要

High-efficiency antimony selenosulfide (Sb_2(S,Se)_3) solar cells are oftenfabricated by hydrothermal deposition and also comprise a CdS buffer layer.Whereas the use of toxic materials such as cadmium compounds should beavoided, both of these issues hinder scaling up to large areas and marketaccess. For this reason, co-sublimation is studied as a manufacturing processfor the active layer as well as the use of Cd-free buffer layers. To furtherimprove the power conversion efficiency (PCE), a graded bandgap profile isdesigned for the absorber layer. A V-shaped graded bandgap in the Sb2(S,Se)3absorber layer is produced on a TiO_2 substrate by co-sublimation of a controlledvarying molar ratio of Sb_2Se_3 and Sb_2S_3. Moreover, increasing theSe/S ratio improves the grain size and favorable (hk1) orientations, reducesthe detrimental bulk defects in Sb_2(S,Se)_3 films. Consequently, the optimizedSb_2(S,Se)_3 solar cells reach a PCE of 9.02%, which is a record value for Cd-freeSb-based solar cells. A PCE of 7.15% is further demonstrated for a Sb_2(S,Se)_3monolithically interconnected minimodule with an active area of 12.32 cm~2.This co-sublimation graded bandgap technique provides a useful guidance forthe optimization of a range of solar cells based on alloy compounds.