Layered Quaternary Compounds in the Cu2S-In2S3-Ga2S3 system.

Several new materials with four structure-types (e.g., Cu0.32In1.74Ga0.84S4 (CIGS4), Cu0.65In1.75Ga1.4S5 (CIGS5), Cu1.44In2.77Ga0.76S6 (CIGS6), and Cu1.1In2.49Ga1.8S7 (CIGS7)) have been evidenced in the Cu2S-In2S3-Ga2S3 pseudo-ternary system. All of them present a 2D structure built upon infinite 2/∞[InS2] layers ((InS6) octahedra sharing edges) on which condense on both sides mono-, bi-, or tri-2/∞[MS] layers ((MS4) tetrahedra (M = Cu, In, Ga) sharing corners). (M(Td))n-2(In(Oh))Sn slabs are separated from each other by a van der Waals gap, and subscript n refers to the number of sulfur layers within the building block. These compounds have the propensity to display stacking faults but also polymorphic forms. Their optical gap (ca. 1.7 eV) is quite similar to the one of the Cu(In0.7Ga0.3)S2 chalcopyrite absorbers used in tandem solar cells, and the major charge carriers are holes. This suggests that they might be very attractive for photovoltaic applications in thin film devices but also for photocatalysis.