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

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Abstract
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 400°C400°C . The grazing incidence X-ray diffraction analysis of these layers established the formation of thin films of ternary composition, Cu2SnS3Cu2SnS3 and Cu4SnS4Cu4SnS4 . Optical bandgaps of the films are direct, 0.95 eV for Cu2SnS3Cu2SnS3 and 1.2 eV for Cu4SnS4Cu4SnS4 , and the electronic transitions are of the forbidden type in both cases. The films are p-type, with electrical conductivities of 0.5–10Ω−1cm−10.5–10Ω−1cm−1 and hole concentrations of 1017–1018cm−31017–1018cm−3 . Based on the optical absorption coefficients, the light generated current density (JL)(JL) as a solar cell absorber was evaluated for these materials for air mass 1.5 (1000W/m2)(1000W/m2) global solar radiation. For a film thickness of 0.5μm0.5μm , Cu2SnS3Cu2SnS3 and Cu4SnS4Cu4SnS4 could offer JLJL of 34 and 27mA/cm227mA/cm2 , respectively. Corresponding optical conversion efficiencies of solar energy into electron–hole pairs are 32 and 24%. The built-in potential for CdS/Cu2SnS3CdS/Cu2SnS3 and CdS/Cu4SnS4CdS/Cu4SnS4 junctions would be above 0.9 V and above 1.1 V when ZnO replaces CdS as the window layer.

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