Molecular\nCross-Linking Enhances Stability of Non-Fullerene\nAcceptor Organic Photovoltaics

Understanding efficiency–durability relationships\nand related\nmitigation strategies is an important step toward the commercialization\nof organic photovoltaics (OPVs). Here, we report that a photoactivated\n6-bridged azide cross-linker (6Bx) improves the morphological stability\nby suppressing the thermally activated diffusion of (Y6) acceptor\nmolecules in PM6:Y6 bulk-heterojunction (BHJ)-based OPVs. Cross-linked\nPM6:Y6 (0.05 wt % 6Bx) BHJ OPVs retain 93.4% of the initial power\nconversion efficiency upon thermal aging at 85 °C for 1680 h\n(<i>T</i><sub>80</sub> = 3290 h). Molecular origins of enhanced\nthermal stability are corroborated by optical spectroscopy, surface\nimaging, 2D solid-state nuclear magnetic resonance (ssNMR), Raman\nspectroscopy, scanning electron diffraction (SED) measurements, and\nanalysis of the BHJ thin films. The facile single-step cross-linking\nstrategy in conjugation with advanced characterization methods presented\nin the study paves the way toward developing durable OPVs based on\nnon-fullerene acceptors (NFAs).