Polymorphic Graphene-like Cuprous Germanosulfides with a High Cu-to-Ge Ratio and Low Band Gap

Abstract

Metal chalcogenides based on heterometallic Ge–Cu–S offer dual attractive features of lattice stabilization by high-valent Ge⁴⁺ and band gap engineering into solar region by low-valent Cu⁺. Herein via cationic amine intercalation, we present three new copper-rich materials with the Cu-to-Ge ratio as high as 3. Two different patterns of Cu–Ge–S distribution could be achieved within each honeycomb sheet. The decoration of such honeycomb sheet by −Cu−S− chain or self-coupling between two honeycomb sheets leads to two layer configurations with different thickness and band gaps. The band gap of these new phases (2.06–2.30 eV), tuned by the layer thickness and the Cu/Ge ratio, represents a significant red shift over known Cu–Ge–S phases with lower Cu/Ge ratios