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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.

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The self-trapping of a free carrier in transition-metal oxides can lead to a small polaron, which is responsible for the inadequate performance of the oxide-based optoelectronic applications. Thus, fundamental understanding of the self-trapping mechanism is of key importance for improving the performance of these applications. Herein, the self-trapping in Co 3 O 4 epitaxial monocrystalline films is investigated primarily by transient absorption spectroscopy. The spectral evolution corresponding to the ultrafast transition from free carriers to small polarons is identified, which allows us to extract the self-trapping kinetics. The relationship between the self-trapping rate and temperature suggests a lack of thermal activation energy. A barrierless self-trapping mechanism derived from the small polaron framework is then proposed, which can successfully describe the observation that self-trapping rate decreases linearly with increasing temperature. Given that small polarons are ubiquitous in transition-metal oxides, this self-trapping mechanism is potentially a general phenomenon in these materials.

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