Nonfused Dimethoxybenzene Electron Acceptors in Organic Solar Cells: From Molecular Design to Structure-Performance Relationship

The photovoltaic mechanism of asymmetric non-fullerene acceptors (NFAs) has not been sufficiently understood, although it is developing as a forceful method to design effective organic solar cells. This article systematically investigated and designed several configurations of nonfused acceptors at the micro level. Skeletons were constructed by a central 1,4-dimethoxybenzene core and flanked by different dithieno-pyrroles and thiophene derivates as electron-donating groups; the end-capped groups were composed of two 1,1-dicyanomethyl-3-indanone. Through theoretical calculation, one found that the designed DBPT series possessed narrower gaps, broadened the absorption to the near-infrared region, larger electron-accepting power, and separated the distance of holes and electrons. They also yielded enhancement mobility, which may relate to the significant dipole moment and electronic coupling. Furthermore, we constructed the device models by using PBDB-T as the donor. The heterojunction model results show that the optimized blends of PBDB-T/DBPT-4F achieved more intermolecular fragment charge amounts, more CT states, and smaller binding energy, showing a significant charge separation/recombination ratio. Then, under the macro-scale model, the device PBDB-T/DBPT-4F has a better power conversion efficiency of 14.69%, owing to a large simulated JSC of 18.82 mA cm-2, consistent with the trend of better interfacial transfer property. This work provided the global description of the molecular light response and the microscopic physicochemical mechanism of the intermolecular charge transfer process, which also sheds light on the structure- property relationship of unfused asymmetric NFAs and enables the strategy to develop valuable OSCs.