A theoretical framework for microscopic surface and interface dipoles, work functions, and valence band alignments in 2D and 3D halide perovskite heterostructures

We propose a computational methodology that highlights the intimate connection between surface and interface dipoles and work functions or valence band alignments. We apply the methodology to inspect the energy level alignments of halide perovskites considering: (i) the effect of surface termination and the ability to fine-tune and interpret the shift in energy alignments via (ii) surface coating and (iii) surface functionalization and/or passivation with molecules. We highlight the importance of local strain relaxation at the surfaces or interfaces and revisit classical approaches based on capacitor models. Finally, we show that surface dipoles are additive in heterostructures and illustrate it through a 2D/3D perovskite interface. This provides a handy tool to interpret band alignments in complex perovskite-based heterostructures and buried interfaces. The scope of our work goes far beyond halide perovskites and allows bridging results from atomistic ab initio calculations and classical simulation approaches for multilayered thin film devices.