Level Alignment in Large-Scale Hybrid Organic-Inorganic Systems from Hybrid Density Functional Theory

Hybrid organic-inorganic systems allow to combine the properties of organic and inorganic substances at the nanoscale and hence open up a wide area for design of new materials with tunable properties. The positions of carrier levels and their alignment determine electronic properties of hybrid materials. A key challenge is that the systems in question tend to be large, due to alignment of components with inherently different lattice parameters or due to complex crystal structure packing. We here use hybrid density functional theory (FHI-aims all-electron code) for systems comprising over 1,000 atoms to reliably predict level alignments in two types of systems. For the paradigmatic interface system tetracene and pentacene at H/Si(111), we demonstrate the necessity of choosing large cells of up to 1,200 atoms that reflect the coincidence pattern and find type II heterojunction behavior with potential separation of charge between organic and inorganic component. For a layered double perovskite we demonstrate how level alignment between organic and inorganic compound is affected when the metal ion is exchanged, and rationalize experimentally observed photoluminescence in these systems.