Surface Treatment of Inorganic CsPbI3 Nanocrystals with Guanidinium Iodide for Efficient Perovskite Light-Emitting Diodes with High Brightness

Highlights A facile and effective surface passivation strategy was demonstrated to improve the optical and stability of CsPbI 3 nanocrystals by using guanidinium iodide post-treatment. Guanidinium cations was shown to be compatible with CsPbI 3 perovskite, leading to significantly improved surface properties of CsPbI 3 nanocrystals. Performance of the CsPbI 3 nanocrystal-based light-emitting device was enhanced by 3.6 folds. The remarkable evolution of metal halide perovskites in the past decade makes them promise for next-generation optoelectronic material. In particular, nanocrystals (NCs) of inorganic perovskites have demonstrated excellent performance for light-emitting and display applications. However, the presence of surface defects on the NCs negatively impacts their performance in devices. Herein, we report a compatible facial post-treatment of CsPbI 3 nanocrystals using guanidinium iodide (GuI). It is found that the GuI treatment effectively passivated the halide vacancy defects on the surface of the NCs while offering effective surface protection and exciton confinement thanks to the beneficial contribution of iodide and guanidinium cation. As a consequence, the film of treated CsPbI 3 nanocrystals exhibited significantly enhanced luminescence and charge transport properties, leading to high-performance light-emitting diode with maximum external quantum efficiency of 13.8% with high brightness (peak luminance of 7039 cd m −2 and a peak current density of 10.8 cd A −1 ). The EQE is over threefold higher than performance of untreated device (EQE: 3.8%). The operational half-lifetime of the treated devices also was significantly improved with T 50 of 20 min (at current density of 25 mA cm −2 ), outperforming the untreated devices (T 50 ~ 6 min).