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

Abstract

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 (V_OC) of 0.916 V, short-circuit current density (J_SC) 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 V_OC 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 J_SC 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.