Selenophene-containing benzodithiophene based donors with different alkyl chains in terminal groups for high-performance all-small-molecule organic solar cells

Abstract

Two small molecule (SM) donors, named CBTSeHR and CBTSeEHR, have been constructed by introducing selenophenes and chlorine atoms simultaneously into the conventional benzodithiophene–terthiophene–rhodanine architecture. In comparison with the non-chlorinated and thiophene based counterpart, the new SM donors exhibit a red-shifted absorption band, lower highest occupied molecular orbital (HOMO) energy levels, stronger intermolecular packing and higher molecular crystallinity. When combined with non-fullerene molecule FO-2Cl, the optimized all-small-molecule organic solar cells (ASM-OSCs) based on CBTSeEHR give a moderate power conversion efficiency (PCE) of 9.30%. Notably, CBTSeHR based devices achieve an outstanding performance of 12.10% with a high open-circuit voltage (V_oc) of 0.881 V, short-circuit current densities (J_sc) of 18.76 mA cm⁻² and fill factor (FF) of 0.732, benefiting from the deep HOMO level, good light-harvesting ability and favorable morphology in the active layer. These findings provide an effective strategy to develop the medium band-gap SM donors for high-performance ASM-OSCs.