Halide Perovskites

Perovskites are a chemically diverse family of materials that are being studied intensely due to a wealth of properties including ferroelectricity, ferromagnetism, superconductivity and many more. Only recently, hybrid organic-inorganic halide perovskites have been (re)discovered as highly efficient photovoltaic absorber materials and solar cells based on such perovskites have exceeded power conversion efficiencies of 25%. Their complex phase diagrams, intricate structure, and multi-scale phenomenology, however, pose challenges to theory and experiment alike. In close collaboration with experimentalists, we are working on computing accurate spectroscopic properties to better understand and tune the electronic structure of existing halide perovskites and predict new, environmentally benign materials.

In the last years, we have been particularly involved in predicting and understanding the electronic structure and dynamics of halide double perovskites and their 2D derivatives. In close collaboration with the Karunadasa lab@Stanford, we have elucidated the indirect-to-direct band gap transition that is observed in some of these systems when they are reduced to the monolayer limit. Density functional theory calculations are playing a vital role in disentangling the intricate interplay of d-orbital interactions, spin-orbit coupling, structural distortions and dimensional reduction that is relevant in these systems.

We have also been involved in developing a "pencil and paper" (LCAO) method for predicting relevant features of the band structure of these systems. However, accurate predictions of electronic and optical properties rely on first principles calculations based on density functional theory and Green's function-based many-body perturbation theory. In this respect, we are working on developing improved methods for this particularly challenging family of materials.

Ongoing work is focused on the structural dynamics and optical properties of 3D and 2D (double) perovskites, and exploring defect dynamics and the surface/interface properties of these materials. Some of our recent papers on halide perovskites include: