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

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.