Suppressing Exciton–Vibration Coupling and Reducing Nonradiative Energy Loss in Conjugated Polymers Through Fluorine Substitution in Side Chains

Fluorine (F) substitution in polymers modulates both molecular energy levels and film morphology; however, its impact on exciton–vibrational coupling and molecular reorganization energy is often neglected. Herein, we systematically investigated F-modified polymers (PBTA-PSF, PBDB-PSF) and their nonfluorinated counterparts (PBTA-PS, PBDB-PS) through simulations and experiments. We found that F atoms effectively lower the vibrational frequency of the molecular skeleton and suppress exciton–vibration coupling, thereby reducing the nonradiative decay rate. Moreover, introducing F atoms significantly decreases the reorganization energy for the S₀ → S₁ and S₀ → cation transitions while increasing the reorganization energy for the S₁ → S₀ and cation → S₀ transitions. These changes facilitate exciton dissociation and reduce the energy loss caused by dissociation and nonradiative recombination of excitons. Additionally, introducing F atoms into polymers enhances the π–π stacking strength and the crystal coherence length in both neat and blended films, ultimately resulting in improvements in the power conversion efficiency of PBTA-PSF:L8-BO and PBDB-PSF:L8-BO are 16.51% and 17.59%, respectively. This study provides valuable insights for designing organic semiconductor materials to minimize energy loss and achieve a higher power conversion efficiency.