Stabilizing Perovskite Light-Emitting Diodes by Incorporation of Binary Alkali Cations

The poor stability of perovskite light-emitting diodes (PeLEDs) is a key bottleneck that hinders commercialization of this technology. Here, the degradation process of formamidinium lead iodide (FAPbI(3))-based PeLEDs is carefully investigated and the device stability is improved through binary-alkalication incorporation. Using time-of-flight secondary-ion mass spectrometry, it is found that the degradation of FAPbI(3)-based PeLEDs during operation is directly associated with ion migration, and incorporation of binary alkali cations, i.e., Cs+ and Rb+, in FAPbI(3) can suppress ion migration and significantly enhance the lifetime of PeLEDs. Combining experimental and theoretical approaches, it is further revealed that Cs+ and Rb+ ions stabilize the perovskite films by locating at different lattice positions, with Cs+ ions present relatively uniformly throughout the bulk perovskite, while Rb+ ions are found preferentially on the surface and grain boundaries. Further chemical bonding analysis shows that both Cs+ and Rb+ ions raise the net atomic charge of the surrounding I anions, leading to stronger Coulomb interactions between the cations and the inorganic framework. As a result, the Cs+-Rb+-incorporated PeLEDs exhibit an external quantum efficiency of 15.84%, the highest among alkali cation-incorporated FAPbI(3) devices. More importantly, the PeLEDs show significantly enhanced operation stability, achieving a half-lifetime over 3600 min.