Theoretical studies on the effects of π-bridge engineering on the photoelectric performance of Y6

Molecular engineering of high performance non-fullerene acceptors (NFAs) is critical to enhance the power conversion efficiencies (PCEs) of bulk heterojunction organic solar cells (BHJ OSCs). In this work, the density functional theory (DFT) and time-dependent DFT are employed to investigate the effects of π-bridge engineering on the photoelectric performance of high-performance NFA Y6. This π-bridge engineering principally involves 1) inserting different types of π-bridge units between the fused-ring core and the terminal unit of Y6, and then the π-bridge unit with better performance is screened for the next study, 2) inserting different numbers of screened π-bridge units between the fused-ring core and the terminal unit of Y6, and 3) modifying the side chains of the screened π-bridge unit with halogen atoms. Theoretical results predict that the selenophene π-bridge has superior properties in terms of dipole moment, exciton binding energy, and light absorption compared with other π-bridge units. In addition, studies on different numbers of selenophene π-bridges suggest that increasing the number of selenophene π-bridges has significant advantages in enhancing light absorption and electron transport capabilities for enhancing the short circuit current density (JSC). Meanwhile, the study of π-bridged side chains substituted with different halogen atoms indicates that the substitution of halogen atoms can play a significant role in reducing the exciton binding energy and raising the transferred charge amounts. The results obtained in this work are expected to be used to design new Y6 derivatives.