Switching from acceptor to FRET donor: how the organic solar cell architecture can change the role of a chromophore

A fused ring non-fullerene acceptor o-IDT-BT-DCV was used in binary and ternary OSCs. The optimised binary device with o-IDT-BT-DCV as the acceptor and PM6 as the donor had a maximum PCE of 10.8%, while incorporation of o-IDT-BT-DCV into a donor:acceptor PM6:Y6 blend delivered a ternary OSC with a maximum PCE of 16.2%. The results combined from fs-TAS, TPV and TPC measurements showed that o-IDT-BT-DCV in the ternary blend did not behave as an acceptor, as it did in the binary film with PM6. Instead, it contributed to charge carrier generation through a sub-picosecond energy transfer process to Y6, followed by a photoinduced hole transfer mechanism with PM6 and/or spontaneous exciton dissociation within the Y6 phase. Besides, the ternary blends were found to be more stable than the binary blend OSCs.