Elucidating the photodegradation pathways of polymer donors for organic solar cells with seven months of outdoor operational stability

The operating lifetime under real-world climates is a critical metric to evaluate the commercial potential of any photovoltaic technology. Organic solar cells (OSCs) have experienced rapid breakthroughs in performance over the past decade owing to advances in device and materials engineering, including interfaces, electron acceptors, and donors. However, the intrinsic photodegradation of polymer donors remains poorly understood, and a path to stable OSCs is yet to be demonstrated under outdoor testing conditions. Herein we elucidate the side-chain-induced degradation mechanism in polymer donors and present an outdoor stability database covering 15 representative non-fullerene-based OSCs, supported by in-lab photostability and thermostability analysis. By understanding the performance losses induced by several photoactive layers and interfaces, we demonstrate that encapsulated non-fullerene-based OSCs can retain 91% of the initial efficiency after seven months of operation under hot and sunny Saudi Arabian climates. These findings reveal encouraging prospects of non-fullerene-based OSCs for outdoor applications.