Suppressing Kinetic Aggregation of Non-Fullerene Acceptor via Versatile Alloy States Enables High-Efficiency and Stable Ternary Polymer Solar Cells

Despite considerable advances devoted to improving the operational stability of organic solar cells (OSCs), the metastable morphology degradation remains a challenging obstacle for their practical application. Herein, the stabilizing function of the alloy states in the photoactive layer from the perspective of controlling the aggregation characteristics of non-fullerene acceptors (NFAs), is revealed. The alloy-like model is adopted separately into host donor and acceptor materials of the state-of-the-art binary PM6:BTP-4Cl blend with the self-stable polymer acceptor PDI-2T and small molecule donor DRCN5T as the third components, delivering the simultaneously enhanced photovoltaic efficiency and storage stability. In such ternary systems, two separate arguments can rationalize their operating principles: (1) the acceptor alloys strengthen the conformational rigidity of BTP-4Cl molecules to restrain the intramolecular vibrations for rapid relaxation of high-energy excited states to stabilize BTP-4Cl acceptor. (2) The donor alloys optimize the fibril network microstructure of PM6 polymer to restrict the kinetic diffusion and aggregation of BTP-4Cl molecules. According to the superior morphological stability, non-radiative defect trapping coefficients can be drastically reduced without forming the long-lived, trapped charge species in ternary blends. The results highlight the novel protective mechanisms of engineering the alloy-like composites for reinforcing the long-term stability of NFA-based ternary OSCs.

Automated summary

Introducing alloy-like composites to strengthen the photoactive layer of organic solar cells can improve their storage stability and enhance efficiency.