Structural optimization of acceptor molecules guided by a semi-empirical model for organic solar cells with efficiency over 15%

Despite much progress in organic solar cells (OSCs), higher efficiency is still the most desirable goal and can indeed be obtained through rational design of active layer materials and device optimization according to the theoretical prediction. Herein, under the guidance of a semi-empirical model, two new non-fullerene small molecule acceptors (NF-SMAs) with an acceptor-donor-acceptor (A-D-A) architecture, namely, 6T-OFIC and 5T-OFIC, have been designed and synthesized. 6T-OFIC exhibits wider absorption spectrum and a red-shifted absorption onset (lambda(onset)) of 946 nm due to its extended conjugation central unit. In contrast, 5T-OFIC with five-thiophene-fused backbone has an absorption with the lambda(onset) of 927 nm, which is closer to the predicted absorption range for the best single junction cells based on the semi-empirical model. Consequently, the device based on 5T-OFIC yields a higher power conversion efficiency (PCE) of 13.43% compared with 12.35% of the 6T-OFIC-based device. Furthermore, an impressive PCE of 15.45% was achieved for the 5T-OFIC-based device when using F-2Cl as the third component. 5T-OFIC offers one of a few acceptor cases with efficiencies over 15% other than Y6 derivatives.