Structurally Stable and Highly Enhanced Luminescent Perovskite Based on Quasi-Two-Dimensional Structures upon Addition of Guanidinium Cations

Lead halide perovskites have received much attention as light emitting materials owing to their excellent photoelectronic properties. Despite their high efficiency as light-emitting diodes (LEDs), only a few lead bromide perovskite (APbBr₃)-based devices have been developed due to their low stabilities and/or the formation of undesirable phases under ambient condition. This work demonstrates that the addition of a small quantity of guanidinium (GUA) A-site cations into an all-inorganic CsPbBr₃ perovskite framework leads to the formation of multidimensional perovskites, with enhanced photoluminescence efficiency due to charge carrier funneling and a pinhole-free surface morphology. All-inorganic 3D CsPbBr₃ perovskite films and GUA-incorporated multidimensional quasi-2D films are employed in the fabrication of green LED devices with an inverted structure of glass substrate/indium tin oxide (ITO)/zinc oxide (ZnO)/poly(ethylenimine) (PEI)/perovskite/poly(9-vinylcarbazole) (PVK)/WO₃/Al. With the addition of GUA A-site cations, the LEDs based on GUA-incorporated perovskite thin films exhibited much higher brightness of ∼10000 cd m^-2 and current efficiency of 9.4 cd A^-1 compared to those of Cs-only perovskite thin film LEDs (∼400 cd m^-2 and 0.2 Cd A^-1, respectively).