Microscopic connection between absolute valence energy alignment and surface dipoles in halide perovskite heterostructures

National audienceIn recent years, hybrid organic-inorganic perovskites (HOP) have undergone extensive research due to their excellent photovoltaic and optoelectronic properties. To further improve their device performance, there is a considerable ongoing research effort on their surface passivation and/or functionalization. This stems from the fact that surface passivation and/or functionalization, including the combination of 2D and 3D perovskites, directly influences the surface dipoles between adjacent layers in a device stack, which in turn changes materials' work functions and absolute energy level alignments. However, the link between the two lacks a general framework bridging classical electromagnetism and modern atomistic approaches. Shedding more light on this link is of great technological importance to fully exploit the potentials of these semiconductors. Hence, this contribution presents a theoretical methodology thatclearly shows the relationship between surface dipoles and work functions. We rely on a semiclassical approach, that will allow scientists not specialized in DFT computation, to make use of their chemical or physical intuitions. We demonstrate the potentials of the methodology through a variety of cases to clearly show i) the effect of surface termination on the absolute energy level alignments, the ability to modulate the work function via ii) surface coating and iii) surface functionalization and/or passivationwith molecules. Finally, we demonstrate the additivity of surface dipoles in heterostructures, which is analogous to the additivity of the dielectric susceptibility in these compounds. Our methodology transcends the limits of halide perovskites and provides a computational strategy to fine-tune the absolute energy level alignments for optimizing the performance of broader families of optoelectronic device