Exploring Polaronic, Excitonic Structures and Luminescence in Cs₄PbBr₆/CsPbBr₃

Abstract

Among the important family of halide perovskites, one particular case of all-inorganic, 0-D CsPbBr and 3-D CsPbBr-based nanostructures and thin films is witnessing intense activity due to ultrafast luminescence with high quantum yield. To understand their emissive behavior, we use hybrid density functional calculations to first compare the ground-state electronic structure of the two prospective compounds. The dispersive band edges of CsPbBr do not support self-trapped carriers, which agrees with reports of weak exciton binding energy and high photocurrent. The larger gap 0-D material CsPbBr, however, reveals polaronic and excitonic features. We show that those lattice-coupled carriers are likely responsible for observed ultraviolet emission around ∼375 nm, reported in bulk CsPbBr and CsPbBr/CsPbBr composites. Ionization potential calculations and estimates of type-I band alignment support the notion of quantum confinement leading to fast, green emission from CsPbBr nanostructures embedded in CsPbBr.

Pressure-induced emission of cesium lead halide perovskite nanocrystals

“…The binding energy of STE (relative to a free exciton) was calculated by the equation: E b  =  E (GS) +  E g  –  E (exciton), where E (GS) and E (exciton) are the total energies of the ground state and the STE state, respectively, and E g is the band gap. Our results on the ambient-pressure phase of Cs 4 PbBr 6 are qualitatively in agreement with the previous studies 21,38 , though different exchange correlation functionals were used.…”

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…Recent transient absorption measurements on green luminescent Cs 4 PbBr 6 films by Yin et al 19 were interpreted by assuming a short polaron lifetime of ∼2 ps, and the hypothesis of polaronic features in Cs 4 PbBr 6 was confirmed by other groups. 41 However, the transient absorption data strongly resemble those of colloidal CsPbBr 3 NCs, as was reported by Wu et al 99 In both the works of Yin et al and Wu et al, at fast delay times (0.2–0.5 ps), an exciton bleach was observed at the lowest-energy excitonic band, and an exciton absorption feature was observed 15 nm above the band edge. Moreover, in both the green luminescent Cs 4 PbBr 6 films of Yin et al and the CsPbBr 3 NCs of Wu et al, the exciton-induced shift almost completely disappeared after 2 ps, and the TA spectra only exhibited exciton bleach at the bandgap.…”

Structure and optical properties of perovskite-embedded dual-phase microcrystals synthesized by sonochemistry

“…CsPbBr 3 NCs. ε/ε 0 = 3.1 was calculated for Cs 4 PbBr 6 by a density functional theory 18 . The spectral shifts we measured from the spectra indicate d = 6.2 nm and 5.6 nm, respectively.…”