Ternary Organic Solar Cells with Reduced Graphene Oxide–Sb₂S₃ Hybrid Nanosheets as the Cascade Material

Abstract We demonstrate that the efficiency of a poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)](PCDTBT):[6,6]‐phenyl‐C₇₁‐butyric‐acid‐methyl‐ester (PC₇₁BM) bulk heterojunction solar cell can be improved from 5.53 % to 6.81 % by incorporating reduced graphene oxide–antimony sulfide (rGO–Sb₂S₃) hybrid nanosheets as the third component. By using this hybrid as the cascade material, we combine the ultra‐conductive multi charge transfer paths provided by graphene with the favorable arrangement of the material energy bands due to the presence of Sb₂S₃ nanocrystals. The higher lowest unoccupied molecular orbital (LUMO) energy level of rGO–Sb₂S₃ relative to PC₇₁BM results in an increase of the open circuit voltage upon increasing the rGO–Sb₂S₃ concentration, while the photocurrent and fill factor are enhanced due to the presence of more exciton dissociation interfaces and more efficient charge transport.