Boosting Charge Generation in Ternary PM6/L8-BO:PCBM Films through a High-Energy Charge Transfer State.

The ternary strategy represents a promising approach to improving the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the mechanism of the third component in optimizing both the active layer morphology and charge transfer processes remains elusive. Here, we employ a multiscale computational framework integrating first-principles calculations, molecular dynamics (MD), and kinetic Monte Carlo (KMC) simulations to elucidate the critical function of PCBM as a third component in the PM6/L8-BO blend. Our findings reveal that PCBM primarily localizes at the PM6/L8-BO interface, forming an additional high-energy charge transfer (H-CT) state between PM6 and PCBM, alongside the intrinsic low-energy CT (L-CT) state between PM6 and L8-BO. This H-CT establishes a new high-efficiency pathway for PM6 exciton dissociation, succeeding in leading to a much larger charge separation (CS) rate (6 × 10 s) than that (5 × 10 s) via the L-CT state. Furthermore, PCBM incorporation improves electron and hole mobilities as well as ambipolar transport, thereby suppressing charge recombination loss. This work unveils the dual role of PCBM in optimizing interfacial charge-transfer kinetics and bulk carrier transport, offering fundamental guidelines for a third-component design in high-performance ternary OSCs.