Unraveling the Role of Crystallization Dynamics on Luminescence Characteristics of Perovskite Light-Emitting Diodes

Metal halide perovskites are one of the most promising materials for optoelectronic applications owing to their unique optoelectronic properties. In the pursuit of achieving the efficient perovskite light-emitting diodes (PeLEDs), the critical role of crystallization dynamics on luminescence properties of cesium lead bromide (CsPbBr₃) perovskite films has been clarified based on the characterizations of in situ photoelectron spectroscopy, synchrotron-based grazing incidence X-ray diffraction, and device fabrication. The crystallinity and crystal orientation of CsPbBr₃ perovskite films has been effectively controlled when tuning the underlayer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) with the ethanolamine modification. The fast crystallization with the formation of pure cubic phase (α-CsPbBr₃) reveals a substantial boost in luminance and device efficiency of PeLEDs, whereas the performance degradation occurs due to the phase transition from α-CsPbBr₃ to orthogonal phase (γ-CsPbBr₃) along with the appearance of PbBr₂. The decomposition of organic additives in the perovskite films is a key factor that results in this phase transition, which changes the absorption and band gap as confirmed by the density functional theory calculation. These experimental and theoretical findings provide a better understanding of the crystallization dynamics of perovskite emitters and their influence on device performance by tuning the substrate properties.