Vacuum evaporation deposited RbxCs1-xPbBr3 thin films for spectrally tunable and stable all-inorganic blue light-emitting diodes

Abstract

Perovskite light emitting diodes (PeLEDs) have emerged as a promising technology for new display applications due to their high color purity and precisely adjustable band gap. However, compared to green and red PeLEDs, blue PeLEDs suffer from lower luminous efficiency and stability. Traditionally, pure blue perovskite luminescence is achieved using mixed halogens, which often leads to phase separation issues. In this paper, we directly introduced RbBr and prepared Rb_xCs_1-xPbBr₃ (x = 0.5,0.6,0.7) thin films using thermal evaporation, achieving wavelength-tunable and stable blue light emission ranging from 477 nm to 489 nm.This is the first report of using thermal evaporation for the fabrication of Rb_xCs_1-xPbBr₃ films. PeLEDs based on these films exhibited stable electroluminescence under varying driving voltages. Operated continuously over 30 min at 6 V in ambient air with 36 % humidity, these devices showed superior spectral stability. Using pure bromine-based material Rb_xCs_1-xPbBr₃ (x = 0.5,0.6,0.7) in the light-emitting layer solves the problem of phase separation of mixed halogens and achieves blue-light emission. Additionally, the introduction of Rb⁺ distorts the crystal structure of perovskite. This distortion decreases the bond length of Pb-Br bonds, increases the bond energy, and raises the formation energy of halogen anion vacancies. As a result, the density of perovskite defect states decreases, and thus the stability is enhanced. This work represents a rare example of vacuum thermal-evaporation processed Rb_xCs_1-xPbBr₃ films and all-inorganic perovskite LEDs.