Molecular Cross-Linking Enhances Stability of Non-Fullerene Acceptor Organic Photovoltaics
Sangcheol Yoon, Braulio Reyes-Suárez, Sang T. Pham, Hervé Vezin, Yeny A. Tobón, Myeongjae Lee, Sam Mugiraneza, Brian Minki Kim, Brian Minki Kim, Mariane Yuka Tsubaki Oide, Seongju Yoo, S.C. Lee, Shu Hui Wang, Sean M. Collins, Christopher M. Bates, Yongsup Park, BongSoo Kim, BongSoo Kim, G. N. Manjunatha Reddy, Thuc‐Quyen Nguyen
Abstract
Understanding efficiency–durability relationships and related mitigation strategies is an important step toward the commercialization of organic photovoltaics (OPVs). Here, we report that a photoactivated 6-bridged azide cross-linker (6Bx) improves the morphological stability by suppressing the thermally activated diffusion of (Y6) acceptor molecules in PM6:Y6 bulk-heterojunction (BHJ)-based OPVs. Cross-linked PM6:Y6 (0.05 wt % 6Bx) BHJ OPVs retain 93.4% of the initial power conversion efficiency upon thermal aging at 85 °C for 1680 h ( T 80 = 3290 h). Molecular origins of enhanced thermal stability are corroborated by optical spectroscopy, surface imaging, 2D solid-state nuclear magnetic resonance (ssNMR), Raman spectroscopy, scanning electron diffraction (SED) measurements, and analysis of the BHJ thin films. The facile single-step cross-linking strategy in conjugation with advanced characterization methods presented in the study paves the way toward developing durable OPVs based on non-fullerene acceptors (NFAs).