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.

Automated summary

This study proposes a photophysical correlation model to explain the relationship between electron-phonon coupling and electronic excitation trapping based on the aggregation behaviors of BTP-eC9 in different processed OSCs. By stabilizing intermolecular electron-phonon coupling through the regulation of donor and acceptor materials, the device efficiency of quaternary OSCs is significantly improved to 18.10%, with enhanced thermal stability, providing valuable insights for further boosting photovoltaic stability.