Tuning Exciton Dynamics and Energy Transfer in PM6:Y6-Based Ternary Organic Solar Cells via a Noncondensed Acceptor as a Guest Component

Organic solar cells (OSCs) based on the PM6:Y6 donor–acceptor system have achieved remarkable efficiency. However, further performance enhancement remains constrained by partial exciton utilization, nonradiative recombination losses, and energetic disorder in the active layer. Here, we introduce a noncondensed acceptor, NFA6, as a third component into the PM6:Y6 host binary blend to regulate exciton dynamics and recombination pathways. Spectroscopic investigations including steady-state, time-resolved photoluminescence, and transient absorption under selective excitation reveal pronounced exciton quenching and accelerated charge generation in ternary blends. A significant spectral overlap between emission of NFA6 and absorption of Y6 indicates an efficient energy transfer process, which enhances exciton harvesting and contributes to an increased short-circuit current density ( J SC ). Incorporation of 20% ( w / w ) NFA6 optimizes the nanoscale morphology, promoting efficient charge dissociation and transportation while suppressing bimolecular and trap-assisted recombination. Energetic disorder evaluation further reveals reduced nonradiative losses in the ternary system compared with the binary counterpart. Consequently, the optimized inverted PM6:Y6:NFA6 ternary device achieves a power conversion efficiency of 16.72%, significantly exceeding 14.11% efficiency in the binary PM6:Y6 device fabricated fully under open-air conditions. This enhancement is due to increased J SC, fill factor, reduced voltage loss, improved charge carrier mobility, and prolonged carrier lifetime, confirming more efficient exciton dissociation and suppressed recombination in the ternary system. These findings reveal that the noncondensed acceptor functions primarily as an excitonic sensitizer rather than a direct charge-separating component. This work provides new insights into exciton management strategies for minimizing voltage losses and advancing high-performance ternary OSCs.