Polymorphic graphene-like cuprous germanosulfides with a high Cu-to-Ge ratio and low band gap

Metal chalcogenides based on heterometallic Ge-Cu-S offer dual attractive features of lattice stabilization by high-valent Ge(4+) 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.