Reducing Limitations of Aggregation‐Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron–Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells

The kinetic aggregation of nonfullerene acceptors under nonequilibrium conditions can induce electron–phonon interaction roll‐off and electronic band structure transition, which represents an important limitation for long‐term operational stability of organic solar cells (OSCs). However, the fundamental underlying mechanisms have received limited attention. Herein, a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation is proposed based on the different aggregation behaviors of BTP‐eC9 in bulk‐heterojunction and layer‐by‐layer processed multicomponent OSCs. Two separate factors rationalize their correlation mechanisms: 1) the local lattice and/or molecular deformation can be regarded as the results of BTP‐eC9 aggregates in binary system under continuous heating, which brings about attenuated intermolecular electron–phonon coupling with intensified photocarrier trapping. 2) The higher density of trap states with more extended tails into the bandgap give rise to the formation of highly localized trapped polarons with a longer lifetime. The stabilized intermolecular electron–phonon coupling through synergistic regulation of donor and acceptor materials effectively suppresses unfavorable photocarrier trapping, delivering the improved device efficiency of 18.10% and enhanced thermal stability in quaternary OSCs. These results provide valuable property–function insights for further boosting photovoltaic stability in view of modulating intermolecular electron–phonon coupling. The relationship between intermolecular electron–phonon coupling and trapping of electronic excitation behind kinetic aggregation of nonfullerene acceptors (NFAs) is revealed in multicomponent organic solar cells (OSCs). The synergistic regulation of donor and acceptor materials can prevent unfavorable aggregation of NFAs, maintaining stable intermolecular electron‐phonon coupling to suppress the increase of trap depth and density for photocarrier trapping in quaternary OSCs.