Elucidation of energetic disorder evolution and degradation mechanisms in organic photovoltaic through transient spectroscopic analysis

Organic photovoltaics (OPVs) have emerged as promising next-generation photovoltaic technology owing to their lightweight, flexibility, and solution-processability. However, achieving long-term operational stability remains a critical challenge essential for their commercialization. Previous stability studies have primarily focused on device performance degradation, such as losses in power conversion efficiency (PCE) and on morphological changes within the active layer. While these approaches provide valuable information, they offer limited insight into the fundamental electronic processes governing device degradation. Here, we propose energetic disorder as a key descriptor for understanding degradation mechanisms in OPVs. Energetic disorder reflects the distribution of energy levels within devices and strongly influences charge generation, transport, trapping, and recombination. In particular, an increase in energetic disorder can promote trap-state formation and non-radiative recombination, ultimately leading to device deterioration. In this study, the evolution of energetic disorder under realistic operating stress conditions, including light, heat, and moisture exposure, is investigated and correlated with charge-carrier dynamics. Major degradation pathways, such as thermally induced morphological instability, photo-induced chemical degradation, and moisture-driven interfacial deterioration, are systematically examined. Time-resolved spectroscopic techniques are employed to quantitatively probe charge generation, transport, and recombination processes, and to establish their relationship with changes in energetic disorder. This approach provides a spectroscopic framework for linking degradation-induced electronic structure evolution to device performance loss, offering new insights into the fundamental origins of OPV instability beyond conventional performance-based assessments.