Taming the Stability of Organic Photovoltaics by Nanoconfinement.

Despite the power conversion efficiency (PCE) of organic photovoltaics (OPVs) exceeding 20%, their commercialization remains hindered by inadequate operational stability. The spontaneous evolution of the phase-separated nanostructures of donor-acceptor blends in the active layer toward equilibrium causes aging of the devices. Here, we report that confining the structures in an ultrathin active layer creates a higher energy barrier for the structural fluctuations, thereby resisting device aging. Specifically, nanoconfinement elevates the glass transition temperature (Tg) by 12 °C and the energy barrier for segmental relaxation by 144 kJ/mol. This stabilizes the nanomorphology of the donor-acceptor blends and increases the device lifetime by 15 times. Most importantly, we found that the kinetics of PCE degradation in devices correlates essentially with the molecular dynamics of the active layer. This layer can be modulated by leveraging the confinement effect, therefore providing a key design principle for high-performance, stable OPV devices.