Preparation and photoelectric properties of CsPbBr<sub>3</sub> perovskite nanoplates

Abstract

All inorganic cesium lead halide (CsPbX3, X=Cl, Br, I) perovskites, as a best candidate in perovskite family, have attracted great interest due to their fascinating optical, chemical and semiconducting properties and have demonstrated as potential building blocks in various applications such as photodetectors, light-emitting diodes, solar cells and lasers. Numerous efforts have been made to develop various CsPbBr3 perovskites with tunable morphology such as quantum dots (0-D), nanowires (1-D) and nanoplates (2-D) to achieve desired properties. Among them, anisotropic colloidal quasi- two-dimensional nanoplates have been attracting a great deal of research enthusiasm. In this work, all-inorganic CsPbBr3 perovskite nanoplates were prepared by precisely controlling the synthesis temperature and time in the hot-injection method. The reaction was performed under the protective atmosphere of nitrogen, at 110°C for 5 s and the reaction mixture was cooled by ice-water bath. Afterwards, the solution was purified by centrifugation at 12000 r min-1 and the precipitates were dissolved in n-octane. The structure, morphology and optical properties of as-synthesized CsPbBr3 perovskite nanoplates were characterized and analyzed by the series of characterization techniques. The results show that a sharp PL emission was detected at the peak of 500 nm with a narrow full width at the half maximum (FWHM) of 26 nm. The high-resolution transmission electron microscopy (HR-TEM) showed that the as-prepared CsPbBr3 nanoplates were uniform in size, with an average length of 20–21 nm and a thickness of 3–5 nm. All the above studies evidenced that, the improved high temperature-injection method have yielded the CsPbBr3 perovskite nanoplates with uniform size distribution, high color purity and improved optical properties. In addition, light emitting diode (LED) with CsPbBr3 perovskite nanoplates as the perovskite luminescent layer were fabricated by the simple solution spin-coating and vacuum evaporation technique. The device structure of the LED is ITO/PEDOT:PSS/TFB/CsPbBr3 NPs/TPBI/LiF/Al. In the device configuration, the patterned ITO is used as the anode, the spin-coated TFB with larger hole mobility is used as the hole transport layer, vacuum evaporated TPBI is chosen as the electron transport layer, as-prepared CsPbBr3 perovskite nanoplates are used as the light emitting active layer, and the vacuum evaporated LiF as the electron injection layer with Al cathode. The external quantum efficiency (EQE) of 1.71% and the luminous brightness of 297 cd m-2 was achieved for the LED devices fabricated by the solution method. Moreover, the densification and roughness of CsPbBr3 perovskite nanoplates as the luminescent layers were measured by atomic force microscopy (AFM). The improved efficiency and performance of our device was directly related to the compact and smooth surface of CsPbBr3 luminescent active layer. This result lays a foundation for the fabrication of high efficiency light emitting diode devices by utilizing all-inorganic CsPbBr3, and provides a relatively simple method for the synthesis of CsPbBr3 nanoplates, as well as good repeatability of thin film device fabrication process.