Theoretical exploration of the molecular stacking and charge transfer mechanism of PBQx:Y6 OSCs

The stacking morphology of the active layer molecules of organic solar cells is closely related to the PCE performance. However, experimental techniques are difficult to observe the molecular conformation and dynamic evolution at the atomic scale, which limits the understanding of the active layer charge transfer mechanism and the design of high-performance material molecules. DFT and AIMD methods can simulate the dynamic evolution of molecules at the atomic scale, and we obtained the local molecular stacking morphology of the active layers of PBQx:Y6 (x = 5,6,7) systems by AIMD simulations. The results reveal that PBQ6:Y6 exhibits the highest number of continuous pi-pi stacking molecules and the best ordering. The relatively high Delta E-S1(CTx) (> 0.1 eV) of PBQ7:Y6 results in increased open-circuit voltage loss. Interestingly, we found that the near-overlapping stacking of the D/A interface not only enables S-1/CTX hybridization to reduce Delta E-S1(CTx), but also enables energy level inversion of T-1 and (CT1)-C-3 state to inhibit the non-geminate exciton recombination pathway. This work provides a systematic theoretical exploration of the molecular stacking and charge transfer mechanisms in PBQx:Y6 OSCs, which offer valuable theoretical insights for the development of high-performance photovoltaic devices.