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Quasi‐2D metal halide perovskites (MHPs) are an emerging material platform for sustainable functional optoelectronics, but the uncontrollable, broad phase distribution remains a critical challenge for applications. Nevertheless, the basic principles for controlling phases in quasi‐2D MHPs remain poorly understood, due to the rapid crystallization kinetics during the conventional thin‐film fabrication process. Herein, a high‐throughput automated synthesis‐characterization‐analysis workflow is implemented to accelerate material exploration in formamidinium (FA)‐based quasi‐2D MHP compositional space, revealing the early‐stage phase growth behaviors fundamentally determining the phase distributions. Upon comprehensive exploration with varying synthesis conditions including 2D:3D composition ratios, antisolvent injection rates, and temperatures in an automated synthesis‐characterization platform, it is observed that the prominentn= 2 2D phase restricts the growth kinetics of 3D‐like phases—α‐FAPbI₃MHPs with spacer‐coordinated surface—across the MHP compositions. Thermal annealing is a critical step for proper phase growth, although it can lead to the emergence of unwanted local PbI₂crystallites. Additionally, fundamental insights into the precursor chemistry associated with spacer‐solvent interaction determining the quasi‐2D MHP morphologies and microstructures are demonstrated. The high‐throughput study provides comprehensive insights into the fundamental principles in quasi‐2D MHP phase control, enabling new control of the functionalities in complex materials systems for sustainable device applications.

Solid-state single-photon emitters (SPEs) such as the bright, stable, room-temperature defects within hexagonal boron nitride (hBN) are of increasing interest for quantum information science. To date, the atomic and electronic origins of SPEs within hBN have not been well understood, and no studies have reported photochromism or explored cross correlations between hBN SPEs. Here, we combine irradiation time-dependent microphotoluminescence spectroscopy with two-color Hanbury Brown–Twiss interferometry in an investigation of the electronic structure of hBN defects. We identify evidence of photochromism in an hBN SPE that exhibits single-photon cross correlations and correlated changes in the intensity of its two zero-phonon lines.

Mixed cesium‐ and formamidinium‐based metal halide perovskites (MHPs) are emerging as ideal photovoltaic materials due to their promising performance and improved stability. While theoretical predictions suggest that a larger composition ratio of Cs (≈30%) aids the formation of a pure photoactive α‐phase, high photovoltaic performances can only be realized in MHPs with moderate Cs ratios. In fact, elemental mixing in a solution can result in chemical complexities with non‐equilibrium phases, causing chemical inhomogeneities localized in the MHPs that are not traceable with global device‐level measurements. Thus, the chemical origin of the complexities and understanding of their effect on stability and functionality remain elusive. Herein, through spatially resolved analyses, the fate of local chemical structures, particularly the evolution pathway of non‐equilibrium phases and the resulting local inhomogeneities in MHPs is comprehensively explored. It is shown that Cs‐rich MHPs have substantial local inhomogeneities at the initial crystallization step, which do not fully convert to the α‐phase and thereby compromise the optoelectronic performance of the materials. These fundamental observations allow the authors to draw a complete chemical landscape of MHPs including nanoscale chemical mechanisms, providing indispensable insights into the realization of a functional materials platform.

Understanding the near-field electromagnetic interactions that produce optical orbital angular momentum (OAM) is crucial for integrating twisted light into nanotechnology. Here, we examine the cathodoluminescence (CL) of plasmonic vortices carrying OAM generated in spiral nanostructures. The nanospiral geometry defines a photonic local density of states that is sampled by the electron probe in a scanning transmission electron microscope (STEM), thus accessing the optical response of the plasmonic vortex with high spatial and spectral resolution. We map the full spectral dispersion of the plasmonic vortex in spiral structures designed to yield increasing topological charge. Additionally, we fabricate nested nanospirals and demonstrate that OAM from one nanospiral can be coupled to the nested nanospiral, resulting in enhanced luminescence in concentric spirals of like handedness with respect to concentric spirals of opposite handedness. The results illustrate the potential for generating and coupling plasmonic vortices in chiral nanostructures for sensitive detection and manipulation of optical OAM.