Long-range exciton diffusion in non-fullerene acceptors and coarse bulk heterojunctions enable highly efficient organic photovoltaics

We investigated singlet exciton diffusion in three ITIC derivatives used as electron acceptors in organic photovoltaics (OPVs) by time-resolved photoluminescence volume quenching and exciton-exciton annihilation. The exciton diffusion coefficient was found to be in the range of 0.003-0.007 cm 2 s −1 which leads to a three-dimensional exciton diffusion length of up to 31 nm. We fabricated solar cells using bulk heterojunctions of these acceptors with the electron donor PTB7-Th which showed ∼7% efficiency and large scale phase separation. Our results show that long range exciton diffusion and large domains offer significant advantages for OPVs. Time-resolved photoluminescence measurements provide an accurate estimate of the three-dimensional exciton diffusion length in three ITIC s based non-fullerene acceptors (NFAs).