Halide Perovskite Epitaxial Heterostructures

Abstract

ConspectusThe past decade has witnessed the great success and rapid development of halide perovskite materials in photovoltaics and light-emitting devices, which is due to the inherently high photoluminescence quantum yield, long carrier diffusion length, high light absorption coefficient, great defect tolerance, and remarkable tunability. For example, the record efficiency of perovskite solar cells has ramped up to 25.5%, comparable to single-crystal silicon solar cells. In combination with the facile solution processing, perovskite solar cells have gained tremendous attention and interest from both academia and the photovoltaic market. Moreover, as a newly emerging class of semiconductors with excellent properties and low manufacturing cost, it is also promising and meaningful to explore new applications beyond optoelectronic devices, such as transistors, lasers, and memory devices. To this end, the integration of different halide perovskites into epitaxial heterostructures provides an ideal option. On the other hand, from the perspective of fundamental studies, halide perovskite heterostructures also provide a platform to directly visualize ion migration and to study the charge transfer behavior and anomalous exciton phenomena, etc.The aim of our Account is to summarize the synthetic strategies to achieve halide perovskite epitaxial heterostructures and to highlight the effective routes to stabilize halide perovskites and heterostructures. We focus this Account on two-dimensional (2D) halide perovskites and emphasize the important roles the organic ligands play. Specifically, we discuss our recent findings on the incorporation of conjugated organic ligands into 2D halide perovskites leading to enhanced thermal and environmental stability and suppressed halide interdiffusion in the corresponding heterostructures. Molecular dynamics simulation and low-dose aberration corrected transmission electron microscopy were used as powerful tools to unveil and elucidate the working mechanism of stabilization and anion interdiffusion suppression. Following this strategy, diverse halide perovskite heterostructures between different halides, metals, or organic cations and more complex heterostructures and superlattices can be realized. Due to the reduced ion motion and improved stability, the interface of the heterostructures can be kept quite sharp. In the outlook of this Account, we discuss the challenges and a few promising directions with a special focus on the vertical van der Waals (vdW) heterostructures, which are expected to offer more flexibility in heterostructure integration and more opportunities in studying the charge transfer and carrier interaction along the out-of-plane direction. Moreover, the existence of semiconducting organic ligands provides new insights to tune the carrier and exciton behaviors along both in-plane and out-of-plane directions.