Rational and effective design of nonfullerene acceptors guided by a semi-empirical model for organic solar cell with efficiency over 15%

Although much progress has been made for organic photovoltaics (OPVs), the active layer material design is generally based on a trial and error approach. It is still a challenge to rationally design active layer materials to further improve OPV performance. Herein, guided by a semi-empirical model we have proposed, two new small molecule acceptors, named F-2F and FO-2F, have been designed and synthesized based on an acceptor F-H. With difluoro substituted end group, F-2F shows red-shifted absorption than F-H, but still far from the range required in the semi-empirical model. Thus, with a subtle molecular optimization by inserting oxygen atom into the backbone of F-2F, FO-2F has been designed, which exhibits much red-shifted absorption, close to the preferred absorption range of the semi-empirical model. Blending with donor polymer PM6, OPV device based on FO-2F achieved an impressive PCE of 15.05% with a Voc of 0.878 V, a Jsc of 22.26 mA cm-2 and a notable FF of 0.77. Both the Voc and Jsc are among the predicted range of the model. These results renders molecule FO-2F a new acceptor example which could demonstrates over 15% PCE only observed almost entirely for Y6 series.