Composition‐Dependent Hot Carrier Relaxation Dynamics in Cesium Lead Halide (CsPbX3, X=Br and I) Perovskite Nanocrystals. Issue 15 (20th March 2017) - Chung, Heejae
Abstract: Cesium‐based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot‐carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot‐carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs‐based perovskite (CsPbX3 with X=Br, I, or their mixtures) NCs on the hot‐carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot‐carrier relaxation dynamics with following order: CsPbBr3 (310 fs)>CsPbBr1.5 I1.5 (380 fs)>CsPbI3 NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI3 NC compared to CsPbBr3 NC. Abstract : Significant dependence of the hot‐carrier relaxation rate on the halide (Br, I, or their mixture) is mainly attributable to the density of states for holes in the valence band of CsPbX3 nanocrystals. The hot‐carrier relaxation rate is observed to decrease from CsPbBr3 to CsPbI3 NC. VB=valence band, CB=conduction band.