# Oriented Dipoles in Ordered Ensembles of Confined Lead Halide Perovskite Nanocrystals

## TL;DR

Researchers developed a method to assemble perovskite nanocrystals into ordered structures, enabling control over their dipole orientation for improved photonic device performance.

## Contribution

A novel liquid–air interfacial assembly method was developed to control the orientation of perovskite nanocrystals.

## Key findings

- Monolayer ensembles of perovskite nanoplates with face-down and edge-up ordering were achieved over large areas.
- Dipole orientation factors were modulated from Θ = 0.78 to Θ = 0.48 by controlling nanoplate ordering.
- Ordered assemblies could enhance waveguides, light outcoupling, and photon coherence in photonic devices.

## Abstract

Here, we demonstrated
directed self-assembly of quasi-2D cesium
lead bromide perovskite nanoplates by liquid–air interfacial
assembly. Due to their ionic crystal nature, perovskite nanocrystals
are susceptible to degradation by most polar immiscible sublayer solvents
(acetonitrile, diethylene glycol). We used glyceryl triacetate as
a liquid substrate for nanoplate self-assembly. By tuning the interfacial
energy and volume fraction of nanoplates, we achieved monolayer ensembles
of nanoplates with face-down and edge-up ordering >100 μm2 in area. Controlled ordering of these confined structures
allowed us to access aligned electronic transition vectors in perovskite
nanocrystal thin films. The dipole orientation factor, or proportion
of horizontal dipoles, was modulated from Θ = 0.78 for face-down
assemblies to Θ = 0.48 for edge-up assemblies, which corresponds
to the majority in-plane and out-of-plane emissive modes, respectively.
Control over nanoparticle ordering and dipole orientation in perovskite
nanocrystals could lead to enhanced waveguides, light outcoupling,
and photon coherence in photonic devices.