Boosting Charge Generation in Ternary PM6/L8-BO:PC71BM Films through a High-Energy Charge Transfer State

Abstract

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 PC₇₁BM as a third component in the PM6/L8-BO blend. Our findings reveal that PC₇₁BM primarily localizes at the PM6/L8-BO interface, forming an additional high-energy charge transfer (H-CT) state between PM6 and PC₇₁BM, 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 × 10¹² s^–1) than that (5 × 10⁹ s^–1) via the L-CT state. Furthermore, PC₇₁BM incorporation improves electron and hole mobilities as well as ambipolar transport, thereby suppressing charge recombination loss. This work unveils the dual role of PC₇₁BM in optimizing interfacial charge-transfer kinetics and bulk carrier transport, offering fundamental guidelines for a third-component design in high-performance ternary OSCs.