Synthesis, crystal structure and optical properties of K2Cu2GeS4

•A new layered compound of K2Cu2GeS4 were successfully synthesized via molten thiourea reactive flux method.•The crystal structure is composed of defective anti-PbO like [Cu2GeS4]2- layers which are interleaved by K+ cations.•This compound is a semiconductor with a band gap of 2.3 eV.•This compound is an indirect band gap semiconductor with interesting intermediate band consisting of Ge 4s and S 3p.

A new compound K2Cu2GeS4 was successfully synthesized by using molten thiourea reactive flux method. The structure was determined by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system of space group P2/c with a unit cell of a = 7.063 (3) Å, b = 5.435 (3) Å, c = 11.037 (6) Å and β = 112.83 (3)°. The crystal structure of K2Cu2GeS4 is composed of defective anti-PbO like [Cu2GeS4]2− layers which are interleaved by K+ cations. This compound is a semiconductor with an indirect band gap of 2.3 (1) eV, which is derived from optical absorption spectrum. First principles calculations reveal that K2Cu2GeS4 has interesting intermediate bands consisting of Ge-4s and S-3p orbitals. This new semiconductor is potentially suitable for solar photocatalytic and photoelectric applications.