The photoelectric conversion mechanism is the core foundation of photovoltaic devices, determining their ability to convert sunlight into electricity. For hydrothermally deposited Sb2(S,Se)3 solar cells, it is conventionally recognized that gradient-bandgap Sb2(S,Se)3 was thought to form a heterojunction with flat-bandgap CdS for carrier separation/transport. In this study, we uncover a previously unidentified photoelectric conversion mechanism. Annealing is shown to drive selenium diffusion into CdS, resulting in the formation of gradient bandgap Cd(S,Se). The Cd(S,Se) homojunction-based solar cell unexpectedly delivers a short-circuit current density of 1.43 mA cm-2. This reveals that the electron-hole separation is not exclusively occurred at the Sb2(S,Se)3/Cd(S,Se) interface, the Sb2(S,Se)3 and Cd(S,Se) form a "V"-shaped bandgap mixed absorber layer concurrently separates charge carriers with the remaining Cd(S,Se). Additionally, the Na2S4O6 additive significantly improves the heterojunction performance. These findings reshape the understanding of photoelectric conversion mechanism and guide band alignment design in the hydrothermally deposited Sb2(S,Se)3 solar cells.
Yu et al. (Thu,) studied this question.