Electronic Coupling of Highly Ordered Perovskite Nanocrystals in Supercrystals

Abstract

Assembled perovskite nanocrystals (NCs), known as supercrystals (SCs), can have many exotic optical and electronic properties different from the individual NCs due to energy transfer and electronic coupling in the dense superstructures. We investigate the optical properties and ultrafast carrier dynamics of highly ordered SCs and the dispersed NCs by absorption, photoluminescence (PL), and femtosecond transient absorption (TA) spectroscopy to determine the influence of the assembly on the excitonic properties. Next to a red shift of absorption and PL peak with respect to the individual NCs, we identify signatures of the collective band-like states in the SCs. A smaller Stokes shift, decreased biexciton binding energy, and increased carrier cooling rates support the formation of delocalized states as a result of the coupling between the individual NC states. These results open perspectives for assembled perovskite NCs for application in optoelectronic devices, with design opportunities exceeding the level of NCs and bulk materials.

Halide perovskite artificial solids as a new platform to simulate collective phenomena in doped Mott insulators

“…By comparing results obtained on 9 different NC superlattice samples with the same nominal characteristics, we obtain a value of δ that varies between 40 and 80 meV. The estimated δ allows us to exclude multi-excitons effects, which would cause smaller (10-30 meV) red-shifts in similar systems, [49][50][51][52] and would appear also in disordered NCs. Sample to sample variability manifests also in the fine structure of the ∆R/R signal for ω < 2.37 eV.…”

Metal–Halide Perovskite Nanocrystal Superlattice: Self‐Assembly and Optical Fingerprints

“…A reduction in biexciton binding energy and an increase in carrier cooling rates in superlattices are believed to be responsible for this lower threshold. [131] Another study showed that upon 800 nm excitation, ASE appears in 2D photonic CsPbBr 3 supercrystals at a pump fluence of 10.9 mJ cm −2 , indicating facilitated light coupling between individual nanocrystals. [132] It should be noted that stimulated superfluorescence amplified by modulation of microcavities can also be obtained, which shows quite similar spectral features to ASE.…”

Tiny spots to light the future: advances in synthesis, properties, and application of perovskite nanocrystals in solar cells

“…2a. [59][60][61][62] First-principle calculation revealed the presence of a confined hole state (CHS), with a size-dependent energetic separation in respect to the valence band (VB) edge states, 63 which explains the dependence of Stokes shift with the NC size. It was verified that the absorption from CHS to the conduction band (CB) is dark (not seen in the UV-Vis absorption spectra) due to the low density of state (DOS).…”