Dredging photocarrier trapping pathways via “charge bridge” driven exciton–phonon decoupling enables efficient and photothermal stable quaternary organic solar cells

Abstract

The operational stability of high-performance organic solar cells (OSCs) based on Y-series small-molecule acceptors is hindered by strong photocarrier trapping processes governed by thermodynamic relaxation in the mixed morphological domains. Herein, the signature of photocarrier trapping associated with exciton–phonon coupling is identified by investigating the pump fluence-dependent exciton diffusion and annihilation dynamics. The kinetic fittings with the exciton–exciton annihilation model demonstrate the intensified exciton–phonon coupling under continuous photothermal stress. Then, we show that a feasible “charge bridge” approach, which enables the decoupling of exciton–phonon interactions of bulk heterojunctions, brings about an enhancement in device efficiency and photothermal stability by dredging non-radiative photocarrier trapping pathways. Experimental proof is provided by the design and fabrication of quaternary OSCs with reduced energetic disorder and the generation of trap states, where a “charge bridge” for charge transfer and transport through the interfacial region is constructed by regulating the energy landscape with the introduced polymer donor and acceptor. The revealed intensified exciton–phonon interactions after photothermal aging are suppressed by the proposed “charge bridge” strategy, giving rise to less exciton and charge trapping resulting from improved exciton–phonon decoupling. This work emphasizes the importance of tailoring exciton–phonon coupling behaviors, providing a design pathway for developing efficient and stable non-fullerene OSCs.