Permeation Barriers Grown by Atomic Layer Deposition Endow Non-Fullerene Organic Solar Cells with Damp-Heat Resilience.

Organic solar cells (OSCs) based on nonfullerene acceptors have seen tremendous progress recently, which qualifies them as a serious next-generation photovoltaic technology. However, their long-term stability is still a key issue that needs to be addressed on the way to commercialization. For relevant long-term stability, gas diffusion barriers are needed to protect the OSCs against ambient gases such as oxygen and moisture. Here, we explore gas diffusion barriers grown by atomic layer deposition (ALD) and demonstrate that aluminum oxide barriers grown at 80 °C afford OSCs that can be operated in the maximum power point in ambient air for more than 1000 h without notable degradation. At the same time, we show that under damp heat conditions, i.e., elevated temperature and humidity, better barriers are needed, that require growth temperatures of >80 °C, which are not tolerated by our standard type OSCs. We significantly improve the thermal stability of our OSCs by the introduction of aluminum-doped zinc oxide nanoparticles (AZO-NPs) as electron extraction layers. OSCs using AZO-NPs are shown to withstand the ALD growth of barrier layers up to 120 °C. Finally, by introducing an aluminum oxide/titanium oxide multilayer barrier, we successfully prevent the corrosion of neat aluminum oxide under damp heat conditions, and OSCs encapsulated with these nanolaminates retain above 80% of their initial efficiency after 1000 h at 70 °C/70% relative humidity. Our results contribute to the improved stability of NFA OSCs even in harsh environments.