Tuning the electronic structure of tin and lead halide perovskites through layering, strain, and distortion

Using density functional theory (DFT)-based calculations, we explore the extent to which achievable modes of structural remodeling can tune the near-gap electronic structure of tin and lead halide perovskites with applications in dye-sensitized solar cells. We show that regardless of how atomic layering is achieved – whether by the growth of layered inorganic phases such as the Ruddlesden-Popper series, hybrid perovskites connected by organic linker molecules, or layered perovskite heterostructures – their band gaps can similarly be widened by several tenths of an eV or more. Furthermore, subjecting perovskites to moderate amounts of compressive strain is found to close the band gap, while subjecting them to tensile strain opens it. By allowing distortions to couple to this strain, we reveal possible pathways by which the conduction and valence band edges may be tuned. Because these classes of compounds are known to have band gaps spanning much of the visible region of the solar spectrum, the ability to control their near-gap electronic structure could further optimize their performance in solar energy conversion applications. Throughout this work, trends in band gap are explained based on the effects of atomic layering, quantum confinement, and symmetry on the character and energy of band-edge crystal orbitals