Tunable Electronic Structure of 2D Hybrid Organic-Inorganic Perovskites from a First Principles Approach*

Layered (so-called two-dimensional, 2D) hybrid organic-inorganic perovskites (HOIPs) can be created by combining a wide range of possible inorganic components with an even broader range of organic molecules, offering considerable flexibility to fine-tune their synthesizability and properties. This talk focuses on computational predictions of the electronic (carrier, i.e., electron- and hole-like) energy levels of new 2D HOIP materials. Such predictions pose a considerable challenge due to high required levels of theory and large unit cells (hundreds of atoms) associated with typical 2D HOIPs. We here use high-precision, all-electron hybrid density functional theory including spin-orbit coupling, showing that this combination provides descriptions of the quantum-well like energy level alignment in lead halide based oligothiophene perovskites in excellent agreement with experiments. We then employ the same approach to predictively address the electronic properties of a broad range of further 2D HOIPs, including lead-free (Ag-Bi) based ones. As a final point, we show that the details of the atomic structure used to predict electronic properties matter significantly, even in a qualitative sense, by determining energy level alignments and, therefore, which component (organic or inorganic) forms the band edges. A complete structural understanding of a given target 2D HOIP is thus essential for faithfully predicting the properties that can be leveraged within this promising new semiconductor materials space.
This work is enabled by the very large community of developers and users of the FHI-aims code as well as by close collaborations with leading experimental colleagues, particularly the group of David B. Mitzi (Duke University).