Microscopic morphology independence in linear absorption cross-section of CsPbBr3 nanocrystals

Abstract

Multiple morphologies of colloidal perovskite nanocrystals (NCs) diversify their optical and electronic properties. Among them, the linear absorption cross-section (σ) is a primary parameter to determine their intrinsic photophysical features, and consequently, application potential. Herein, three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr3 NCs, nanocubes (NBs), nanoplatelets (NLs), and nanowires (NWs), were targeted, and their linear σ values were obtained through femtosecond transient absorption (TA) spectroscopy analysis. At high excitation energy well above the bandgap, the σ per particle of all CsPbBr3 NCs linearly increased with the particle volume (VNC) regardless of the morphology with the value of σ400 = 9.45 × 104 cm−1 × VNC (cm2). Density functional theory (DFT) calculation confirmed the negligible influence of shapes on the optical selection rules. The Einstein spontaneous emission coefficients calculated from the σ values define the intrinsic radiative recombination rate. However, reduced size dependence is observed when the excitation energy is close to the bandgap (i.e., at 460 nm) with the value of σ460 = 2.82 × 108 cm0.65 × (VNC)0.45 (cm2). This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs. These results provide in-depth insight into the optical characteristics for perovskite NCs.