Facet-dependent and interfacial plane-related photocatalytic behaviors of semiconductor nanocrystals and heterostructures

Recent studies on polyhedral semiconductor nanocrystals and semiconductor wafers have revealed that their electronic and photocatalytic properties are highly facet-dependent. For example, Cu2O rhombic dodecahedra are highly photocatalytically active, but cubes are inactive. Through density functional theory (DFT) calculations, these observations can be understood because different crystal surface planes display variable band structures, giving rise to tunable degrees of valence and conduction band bending and difficulty to charge carrier migration across these surfaces. In the case of Cu2O cubes, the observed photocatalytic inactivity results from a large barrier height at the {100} face, preventing charge carriers from moving past this crystal surface. Remarkably, growing another semiconductor such as ZnO, CdS, ZnS, or Ag3PO4 nanostructures on Cu2O cubes, octahedra, and rhombic dodecahedra often lead to varying degrees of photocatalytic activity suppression, rather than the expected enhancement. These studies have suggested that the specific contacting lattice planes at the heterojunction can significantly affect charge carrier transport across the interface through a large degree of interfacial band bending, meaning the outcome of photocatalytic activity is highly interfacial plane-related. Such insights are quite important, and imply that solar cells and heterostructured photocatalyst designs need to pay attention to such effects to effectively improve their performance. This Review largely uses examples from our work to illustrate recent advances in the understanding of facet-dependent electronic and photocatalytic properties of semiconductor materials. (C) 2019 Elsevier Ltd. All rights reserved.