Improving all ternary small-molecule organic solar cells by optimizing short wavelength photon harvesting and exciton dissociation based on a bisadduct analogue of [70]PCBM as a third component material

Ternary small-molecule organic solar cells (OSCs) are efficiently optimized and fabricated with small-molecule benzodithiophene terthiophene rhodanine (BTR) as the donor and a blend of Y6 and bisPC71BM or PC71BM as the acceptor. The power conversion efficiencies (PCEs) of BTR:Y6 binary OSCs, BTR:Y6:bisPC71BM and BTR:Y6:PC71BM optimized ternary OSCs are 11.56%, 12.97% and 12.25%, respectively. BTR:Y6:bisPC71BM optimized ternary OSCs show a relatively high open circuit voltage (VOC) of 0.916 V, short-circuit current density (JSC) of 20.2 mA cm−2 and fill factor (FF) of 70.1% compared with BTR:Y6 binary OSCs and BTR:Y6:PC71BM optimized ternary OSCs. The VOC of ternary OSCs monotonically increases with increasing bisPC71BM content in the blend acceptor, which can be mainly ascribed to the shallow LUMO and enlarged energy bandgap. The highest JSC and FF are attributed to the complementary absorption of the BTR:Y6 binary photoactive layer and have good compatibility. We successfully demonstrate that a bisadduct analogue of [70]PCBM (bisPC71BM) is a better third component material than a single analogue of [70]PCBM (PC71BM). The blend of BTR, Y6, and bisPC71BM (the optimized BTR:Y6:bisPC71BM ratio of 1 : 1 : 0.2) is a promising method to prepare efficient ternary OSCs.