3D graphene-like semiconductor Ba2HfTe4 with electronic structure similar to graphene and bandgap close to silicon

Abstract

Summary: Opening the graphene zero bandgap and simultaneously keeping its linear electronic dispersion has been widely accepted as a very challenging scientific puzzle. Moreover, one of the biggest obstacles for all-perovskite tandem solar cells is the lack of perovskite semiconductors with a narrow bandgap (<1.2 eV). Here we examine these two issues and theoretically identify the environmentally friendly perovskite A2HfTe4 (A = Ca, Sr, Ba), especially Ba2HfTe4. This material is a good candidate for three-dimensional graphene-like semiconductors with two-dimensional electronic dimensionality, linear band-edge dispersion, a direct bandgap of 0.77–0.96 eV, carrier effective mass and mobility similar to graphene, visible-light absorption beyond Pb-based perovskites, and power conversion efficiency approaching ∼28%. A2HfTe4 is a promising bottom-cell material that helps achieve all-perovskite tandem solar cells thanks to its narrow bandgap and acts as a potential alternative to the currently popular perovskite-silicon tandem solar cells.

Keywords

• narrow bandgap
• layered chalcogenide perovskite
• electronic structure
• linear dispersion
• flat band
• carrier mobility