Clarify the Cathode Degradation in Perovskite-Based Light-Emitting Diodes

This study investigates the degradation mechanisms of perovskite-based light-emitting diodes (PeLEDs) during storage and reveals the formation of time-dependent non-emissive electroluminescence (EL) regions, known as EL dark patterns, even under relatively inert conditions. Analyses identify cathode degradation as the dominant factor obstructing charge injection and driving the formation of these patterns. Residual moisture/oxygen in the storage environment is implicated in triggering chemical reactions at the aluminum (Al) cathode, likely involving interaction with perovskite degradation. To mitigate this, a strategy of incorporating a polyethyleneimine ethoxylated (PEIE) cathode buffer layer or replacing the conventional 3D perovskite with a quasi-2D structure is introduced. These measures aim to block ion diffusion or suppress ion mobility, delaying EL dark pattern formation. Pairing PEIE with more stable cathodes (indium-zinc oxide (IZO) or silver (Ag)) significantly enhances stability. While EL dark patterns emerge within just 4 h in devices using the conventional LiF/Al cathode, none are observed after 168 h (7 days) or 336 h (14 days) in devices employing PEIE/IZO or PEIE/Ag. This work identifies Al cathode degradation as a primary limitation to PeLED storage stability and highlights the potential of stable electrode materials and interface engineering to extend the lifetime of perovskite optoelectronic devices.