Oligomerized Electron Acceptors with Alkynyl Linkages to Suppress Electron-Phonon Coupling for Low-Energy-Loss Organic Solar Cells.

A novel series of alkynyl-linked oligomerized electron acceptors have been synthesized via Sonogashira coupling. The alkynyl linkages can enhance molecular planarity and aggregation, suppress electron-phonon coupling, and reduce non-radiative losses. Binary organic solar cells (OSCs) achieved an efficiency of 17.90%, with a non-radiative loss of 0.185 eV, while ternary OSCs reached a remarkable efficiency of 19.52%. Oligomerized electron acceptors, featuring molecular weights akin to polymers and well-defined chemical structures, have emerged as promising candidates for organic solar cells (OSCs) due to their consistent batch-to-batch reproducibility and improved thermal stability. In this study, we developed a series of oligomerized electron acceptors incorporating alkynyl linkages via an efficient Sonogashira coupling reaction between alkyne-substituted Y-type precursors and multi-substituted iodobenzenes. This method produced monomeric (S-Alkyne-YF), dimeric (D-Alkyne-YF), and trimeric (T-Alkyne-YF) configurations, enabling systematic control over molecular size and substituent arms. The alkynyl linkages, characterized by high bond strength and planar geometry, enhanced molecular planarity and aggregation in films, thus facilitating precise control over morphology and phase separation in the photoactive layers. Notably, the inclusion of these linkages effectively suppressed electron-phonon coupling, resulting in reduced non-radiative energy losses and elevated photocarrier lifetime. OSCs based on PM6:T-Alkyne-YF achieved a power conversion efficiency of 17.90%, a low non-radiative energy loss of 0.185 eV, and an open-circuit voltage of 0.943 V. Furthermore, integrating T-Alkyne-YF into the D18:N3 blend yielded an exceptional PCE of 19.52%. These results underscore the potential of alkynyl-linked oligomerized acceptors in advancing highly efficient and stable OSCs, offering a viable pathway for reducing electron-phonon coupling and enhancing device performance.