Probing Chemical-Composition-Induced Heterostructures and Interfaces in Lead Halide Perovskites.

Lead halide perovskites (LHP) are of great interest for their optoelectronic properties and photovoltaic applications. Various heterostructures are created in these materials to achieve favorable optical properties and improved stability at the interfaces during the fabrication of devices. Such heterostructures are often assumed to be formed based on the reactivity of precursors and are not directly probed. In this Feature Article, we report how various strategies have been employed in LHP thin films and nanocrystals (NCs) that generate heterostructures to boost their stability and photovoltaic (PV) efficiencies and how variable energy photoelectron spectroscopy (VEPES) can probe the chemical composition variation in heterostructured materials and interfaces. We specifically discussed the internal heterostructures of LHP NCs generated due to the surface chemistry and postsynthesis anion exchange followed by a detailed discussion of the heterostructures induced by the chemical composition (anion, cation, and degradation) of LHP thin films. The difficulties in determining heterostructures as well as the potential scope of the application of VEPES in unwrapping heterostructures in diverse materials are also discussed.