Coherency and Lattice Misfit Strain Critically Constrains Electron-Hole Separation in Isomaterial and Heteromaterial Type-II Heterostructures

Semiconductors with appropriate band-gaps, band-edges, and lower lattice misfit strain have been assembled to form type II heterostructures to promote the electron-hole separation for photoelectrochemical water splitting. For efficient design of type-II coherent heterostructures, it is essential to calibrate the band gaps, band edge positions, bonding, and lattice misfit strain at the interface. To this end, we apply the first principle study to screen type-II heterostructures by exploring native and non-native structures of widely used semiconductor materials such as TiO2, ZnO, BiVO4, CdSe, and ZnS. Non-native structures differ from the native (ground state) structure of bulk crystals in terms of discrete translational symmetry. Due to a change in discrete translational symmetry, atomic, and electronic properties of native and non-native materials are expected to be different. The screening process is based on three criteria: band edges, type-II band alignment between two semiconductors, and identification of coherent interfaces between them. Band edge calculations show that most of the polymorphs are not only suitable for oxygen evolution reaction, but also for the hydrogen evolution reaction. On the basis of band edge positions, several isomaterial and heteromaterial type-II combinations of heterostructures have been explored in which 221 (out of 297) materials have type-II combinations, including many combinations that have not yet been explored experimentally. However, a requirement of the complementary translation symmetry and motif positions to minimize lattice mismatch brings down the possibilities to 19 misfit strained coherent interfaces (e.g., WZ (10 (1) over bar0)-ZnS/ZB (110)-ZnO). This study points to the centrality of constraints of the coherency of the interface in determining the efficiency of electron-hole separation.