First-Principles Studies of Two-dimensional Hybrid Inorganic-Organic Perovskites: Successes and Challenges*

I will discuss our first-principles computational investigations into several interesting aspects of two-dimensional (i.e. layered) hybrid organic-inorganic perovskites, including the organic-inorganic energy level alignment, spin-orbit-coupling induced band splitting, and its coupling with lattice dynamics. In addition to the new insights and understanding we obtained from first-principles modeling in collaboration with experimental groups, I will also highlight key challenges we currently face. 

For a class of two-dimensional hybrid organic-inorganic perovskite semiconductors, the flexibility in varying the organic and inorganic components allows control over the nature, energy, and localization of carrier states in a quantum-well-like fashion. Our first-principles predictions, based on the large-scale hybrid density-functional theory with spin-orbit coupling, show that the interface between the organic and inorganic parts within a single semiconductor can be modulated systematically, enabling us to induce different energy level alignments. Additionally, we show how the spin-orbit-coupling-induced lifting of the spin degeneracy depends indirectly on constituting organic motifs. We examine experimentally synthesized structures, and the effect of the organic spacer cation is elucidated. Interestingly, we observed the momentum-independent persistent spin texture splitting rather than the conventional Rashba/Dresselhaus splitting in one case, and subtle modification to organic cation is found responsible for inducing this interesting material property. I will also discuss how lattice dynamics might induce instantaneous band-splitting and relevant timescales for such temporal changes in centrosymmetric systems. Lastly, I will touch briefly on computational/theoretical challenges for designing hybrid organic-inorganic perovskite semiconductors by discussing progress and challenges in accurate computation of the energy-level alignment and excitons of different characters.