Effects of organic ligands on efficiency and stability of perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) have attracted considerable attention due to their low cost, high efficiency and narrowband emission. However, poor operational lifetime limits their practical application and the degradation mechanism is not yet clear. Herein, the effect of typical phenylalkylamine and alkylamine ligands on optoelectrical properties and operational stability of cesium/methylammonium lead bromide PeLEDs were systematically investigated. The phenylethylamine (PEA) modified PeLED shows a champion maximum external quantum efficiency (EQE) of 9.35%, which is much better than that of phenylmethylamine (PMA) and phenylbutylamine (PBA) modified devices. For alkylamine-based devices, the maximum EQEs gradually rise from 2.72 to 6.33% and 6.66% as increase of alkyl chain length. PEA modified device exhibits the best half-lifetime of 114 min and alkylamine-based devices exhibit almost equal T₅₀ of approximately 20 min. X-ray diffraction measurements show that the dominant diffraction peaks of pervoskite films disappear or shift and scanning electron microscope detected that many pinholes appeared in perovskite films after operation. Combining with the results of X-ray photoelectron spectroscopy, we conclude that the recrystallization of perovskite occurred during the operation causes the film change in morphology and crystallinity, ultimately result in the degradation of PeLEDs. The effect of typical phenylalkylamine and alkylamine ligands on optoelectrical properties and operational stability of PeLEDs were systematically investigated. The phenylethylamine modified PeLED shows a champion maximum EQE of 9.35% and the best operational lifetime of 114 min. We concluded that the decomposition and recrystallization of perovskite occurred during the operation causes the film change in morphology and crystallinity, ultimately result in the degradation of PeLEDs.