Synergistic Vibrational Suppression and Aggregation Control via a Rigid Dimeric Acceptor for 21.13% Organic Solar Cells

The efficiency bottleneck of organic solar cells (OSCs) is predominantly hindered by severe non-radiative energy loss (ΔE₃), which primarily originates from strong electron-phonon coupling and detrimental charge recombination into darker state traps. Herein, we designed and synthesized a highly rigid and polarized dimeric acceptor, DY-SO by incorporating a sulfone bridged unit. It is revealed that the sulfone bridge's steric hindrance restricts backbone torsion and suppresses molecular vibration, enabling DY-SO with significantly reduced reorganization energy compared to small molecule L8-BO, which reduces non-radiative triplet trapping (CT→T₁) and yields photoluminescence quantum yield (PLQY) of 11.70% and exceptionally low ΔE₃ of 0.149 eV. Upon deploying DY-SO into the D18:L8-BO baseline matrix to evaluate its photovoltaic potential, we further discovered that the inclusion of this rigid dimer successfully tames the film-formation kinetics, effectively suppressing the excessive self-agglomeration inherent to rigid structures and promoting more ordered molecular packing and a favorable phase-separated morphology. Benefiting from these synergistic modulations, the optimal ternary D18:L8-BO:DY-SO OSC achieves an outstanding power conversion efficiency of 21.13% (certified as 20.70%). This work demonstrates that by introducing structurally rigidified, highly polarized dimeric acceptor to suppress molecular vibrational coupling, and mitigate non-radiative dissipation is of great significance for improving the performance of OSCs.