Clarify the Cathode Degradation in Organic Lead Halide Perovskite Light-Emitting Diodes

Despite achieving over 30% efficiency in 2023, perovskite light-emitting diodes (PeLEDs) suffer from inherently poor stability during storage, causing significant degradation and short operation lifetimes, severely compromising their viability for practical applications. Consequently, it is imperative to block all intrinsic degradation pathways, necessitating urgent and thorough investigation. In our work, we discovered that even when storing the CH3NH3PbBr3 devices inside a nitrogen-filled glove box with trace amounts of oxygen and moisture levels below 1.0 ppm, there is still a time-dependent formation of non-emissive electroluminescence (EL) patterns in the active areas. By varying hole transport layers, perovskite components from 3D to quasi-2D, and diverse cathode configurations, we demonstrated that these non-emissive EL patterns are linked to the degradation of the metal cathode. Trace moisture, temperature fluctuations, or ion migration initiate a chemical reaction with CH3NH3PbBr3 perovskite, leading to degradation products that compromise the metal cathode, thus posing a challenge to the stability and lifespan of the devices. Remarkably, we found that employing a conductive metal oxide, such as Indium-Zinc-Oxide (IZO), in combination with a polyethyleneimine ethoxylated (PEIE) buffer as the cathode structure (PEIE/IZO), or using PEIE combined with Ag as the cathode (PEIE/Ag) instead of Al, effectively prevents cathode degradation. PeLEDs with Al cathodes exhibited non-emissive EL patterns within just 4 hours of storage in the nitrogen-filled glove box. In contrast, PeLEDs with the PEIE/IZO or PEIE/Ag cathode structures showed no dark patterns in the active areas even after 14 days of storage. Our findings reveal that cathode degradation is a crucial factor limiting the performance and lifespan of PeLEDs. Addressing this issue requires the development of suitable electrode buffers incorporating metal or conductive metal oxide-based cathode configurations. This study effectively resolves a major bottleneck in perovskite light-emitting diodes under unbiased conditions, facilitating the advancement of stable perovskite optoelectronics.