Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals

Abstract

Forster resonant energy transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as an optoelectronic design element to transport energy. However, so far, nanocrystal (NC) systems supported only diffusion lengths of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm 2 /s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (CsPbBr 3 PNCs). Exciton diffusion was directly measured via steady-state and timeresolved photoluminescence (PL) microscopy, with physical modeling providing deeper insight into the transport process. This exceptionally efficient exciton transport is facilitated by PNCs' high PL quantum yield, large absorption cross section, and high polarizability, together with minimal energetic and geometric disorder of the assembly. This FRET-mediated exciton diffusion length matches perovskites' optical absorption depth, thus enabling the design of device architectures with improved performances and providing insight into the high conversion efficiencies of PNC-based optoelectronic devices.

Suppressing Strong Exciton–Phonon Coupling in Blue Perovskite Nanoplatelet Solids by Binary Systems

“…[17] On the other hand, the long-range exciton diffusion in the pure NPL solids will also increase the probability of exciton trapping and further aggravate this behavior. [18] As expected, the 3-ML rich binary NPL systems,w ith much weaker exciton-phonon coupling and shorter exciton diffusion lengths,exhibit asignificant decline in the proportion of long-lived component.…”

Suppressing Strong Exciton–Phonon Coupling in Blue Perovskite Nanoplatelet Solids by Binary Systems

“…[17] On the other hand, the long-range exciton diffusion in the pure NPL solids will also increase the probability of exciton trapping and further aggravate this behavior. [18] As expected, the 3-ML rich binary NPL systems,w ith much weaker exciton-phonon coupling and shorter exciton diffusion lengths,e xhibit as ignificant decline in the proportion of long-lived component.…”

“…On one hand, the self‐trapping exciton will not absolutely result in nonradiative decay, the trapped excitons in the band edge possibly recover to free exciton under strong phonon vibrations, thereby we can see a longer fluorescence lifetime [17] . On the other hand, the long‐range exciton diffusion in the pure NPL solids will also increase the probability of exciton trapping and further aggravate this behavior [18] . As expected, the 3‐ML rich binary NPL systems, with much weaker exciton‐phonon coupling and shorter exciton diffusion lengths, exhibit a significant decline in the proportion of long‐lived component.…”

Improved Stability and Exciton Diffusion of Self‐Assembled 2D Lattices of Inorganic Perovskite Nanocrystals by Atomic Layer Deposition

“…In order to promote this, one needs to implement strategies to maintain the optical stability over time. Therefore, in this manuscript, we expand the work we did in the previous work [ 13 ] by comparing samples with two differently processed protective coatings. Recently, several passivation strategies have been explored in order to overcome the stability issues that hinder the actual employment of PNCs in optoelectronic devices, [ 16 ] most commonly, crosslinking of the surface ligands [ 17 ] or the application of polymeric coatings.…”

“…[ 12 ] In the latter case, it is possible for an exciton to hop onto an adjacent QD by FRET mechanism, provided that other conditions for FRET beyond the short distance are met, for instance a significant degree of spectral overlap between the emission spectrum of the excited QD and the absorption spectrum of the ground state QD that is receiving the exciton. Our group has recently demonstrated FRET‐mediated transport in a carefully engineered system that allowed to create long‐range ordered 2D lattices of close‐packed PNCs [ 13 ] and obtain a record transport of 200 nm, [ 13 ] one order of magnitude larger than what previously observed in close‐packed arrays of inorganic QDs (30 nm) [ 14 ] and PNCs assemblies (up to 50–70 nm). [ 15 ] Here, we expanded our investigation by reporting for the first time a complete spectrally resolved map of the exciton diffusion spot in a similar self‐assembled close‐packed monolayer of PNCs.…”