Fine-tuning the side-chains of non-fullerene small molecule acceptors to match with appropriate polymer donors

Side-chain engineering of donor and acceptor materials is an important topic in the field of organic photovoltaics. The influence of side-chains in active layer molecules on the corresponding photovoltaic device performances is still elusive, especially for the devices based on non-fullerene small molecule acceptors. In this work, we designed and synthesized two non-fullerene acceptors (IDTT-BH and IDTT-OBH) using an indacenodithieno[3,2-b] thiophene (IDTT) moiety as the central building block and (2-3-oxo-2,3-dihydro-1H-cyclopenta[b] naphthalen-1-ylidene) malononitrile (NINCN) as the end-group, which have similar energy levels and optical absorption spectra, and differ in the side-chains. We systematically investigated the effect of the side-chains on the device performance based on these two non-fullerene acceptors pairing with different donor materials. For the devices with J71 and PDCBT as donor materials, IDTT-BH showed better PCEs of 11.05% and 10.35%, respectively. Notably, 10.35% efficiency is among the top values in PDCBT-based OSCs. While, the devices based on PBDB-T: IDTT-OBH showed a better PCE of 10.93% than that of IDTT-BH based devices. It was found that the side-chains of non-fullerene acceptors have an effect on tuning the morphology of blend films and thus affect the photovoltaic performance, and different donor materials should be paired with the acceptors with the most suitable side-chains to achieve the best photovoltaic performance.