CsPbBr₃ Thin Film Grown by Dual-Source Evaporation for PeLED

Recently, researches have focused on perovskite light emitting diodes because of their high color purity and high efficiency. Among them, the inorganic halide perovskite CsPbX₃ (X = Cl, I, Br) has superior optoelectronic properties and stability than the organic halide perovskite. Halide perovskite materials can be synthesized by solution and thermal vacuum evaporation process. Thermal evaporation is suitable for industrial scale-up manufacturing and has no detrimental effect on solvents. In addition, it can be coated uniformly and evenly by precisely controlling the film thickness. In this study, we studied the characteristics of the thin film for the light emitting layer of CsPbBr₃ made by thermal evaporation using dual sources of CsBr and PbBr₂. In the experiment, CsBr and PbBr₂ powders were deposited on a glass substrate by changing the composition ratio of the thin film by controlling the evaporation rate, respectively. CsPbBr₃ shows a γ-Orthorhombic structure at room temperature, but when a temperature in the range of 185°C to 360°C is applied, it has an α-cubic structure and is decomposed at a temperature higher than that. Therefore, we deposited the substrate at room temperature and 300°C. After that, the phase change through annealing and the behaviors of the thin film were observed. At this time, the optical band gap of the CsPbBr3 thin film is about 2.34-2.36 eV and has a value similar to the previously reported 2.3 eV, and the band gap tends to decrease slightly as the post-heat treatment temperature increases. Crystal structure analysis was measured using X-ray diffraction. For surface analysis, microstructures of the deposition and fracture surfaces of the thin film were observed using FE-SEM. Absorbance was obtained using a UV-Vis-NIR spectrophotometer, and photoluminescence (PL) was measured using a fluorescence spectrometer irradiating pulses with a wavelength of 470 nm of an excitation light source. Time-resolved photoluminescence was measured with a 470 nm laser to measure the carrier life time. Finally, the work function and valance band maximum (VBM) were obtained through UPS. In order to know the LED characteristics and efficiency of the deposited thin film, the photoelectric characteristics were checked after stacking the devices while controlling electron transport layer(ETL) and hole transport layer(HTL).