Cu[sub 2]SnS[sub 3] and Cu[sub 4]SnS[sub 4] Thin Films via Chemical Deposition for Photovoltaic Application

Thin films of copper sulfide (CuS, 200 nm thick) were deposited over thin films of tin sulfide (SnS, 180 nm thick) by sequential chemical deposition. The layers were heated in nitrogen atmosphere at 350 and . The grazing incidence X-ray diffraction analysis of these layers established the formation of thin films of ternary composition, and . Optical bandgaps of the films are direct, 0.95 eV for and 1.2 eV for , and the electronic transitions are of the forbidden type in both cases. The films are p-type, with electrical conductivities of and hole concentrations of . Based on the optical absorption coefficients, the light generated current density as a solar cell absorber was evaluated for these materials for air mass 1.5 global solar radiation. For a film thickness of , and could offer of 34 and , respectively. Corresponding optical conversion efficiencies of solar energy into electron–hole pairs are 32 and 24%. The built-in potential for and junctions would be above 0.9 V and above 1.1 V when ZnO replaces CdS as the window layer.