High open-circuit voltage ternary organic solar cells based on ICBA as acceptor and absorption-complementary donors

Ternary organic solar cells (OSCs) are fabricated with indene-C-60 bisadduct (ICBA) as an electron acceptor and the low-band-gap polymer PBDTTT-C-T and the highly crystalline small molecule n-BDT-3T-CNCOO as electron donors. A high open-circuit voltage of 0.98 V is achieved, which is 0.2 V higher than that of ternary OSCs based on phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor. Incorporation of n-BDT-3T-CNCOO promotes the power conversion efficiency (PCE) from 5.01% for polymer binary devices to 5.51% for ternary devices. The improved PCE is attributed to the nanofibrous morphology with enhanced crystallinity of the donors and improved aggregation of the ICBA acceptor, which facilitate charge separation and charge transport. This work reveals that the ternary strategy of blending highly crystalline small molecules enhances PCEs of OSCs based on ICBA and other non-fullerene acceptors.