Aromatic side chain manipulation in A-DA′D-A type acceptors for organic photovoltaics

Organic photovoltaics based on narrow band gap small molecule acceptors (SMAs) having structural tunability have received tremendous attention in recent years because of their high device performance. Side chain engineering can be used to directly tune the molecular packing and energy levels, and therefore the fill factor and VOC in devices, which is a convenient and feasible strategy to improve device efficiency. In the current study, three small molecule acceptors BTP-0-iPr, BTP-1-iPr and BTP-3-iPr based on the Y6 backbone with different side chains were designed, synthesized and characterized. The photoelectric properties and the impact on device performance resulting from the steric hindrance of different aromatic chains linked to the central backbone were discussed. The developed BTP-1-iPr with side chains of 4-isopropylphenyl achieves a power conversion efficiency (PCE) of 17.19%, together with the PM6 donor. The results highlight the potential of phenylalkyl side chains with large steric hindrance for the improvement of photovoltaic performance for devices based on small molecule acceptors. Three acceptors with different aromatic side chains were synthesized and the photovoltaic performance effects of steric hindrances were studied. BTP-1-iPr better matches the energy level of PM6, obtaining higher VOC, FF and PCE of 17.19%.