Studies on the Energy Band Discontinuities in SnS/ZnMgO Thin Film Heterojunction

Tin sulfide (SnS), with a direct energy band gap of 1.3 eV and high absorption coefficient >104 cm-1 is a promising candidate for application as an absorber material for solar cell fabrication. Although several research groups have fabricated SnS-related solar cells, the reported efficiencies were low (< 3.0%). One of the reasons for this low efficiency is the mismatch at the band edges in the heterojunction. In the present work, SnS films have been synthesized by sulfurization of Sn layers deposited by evaporation and RF sputtering onto SnO2 coated glass. The structural properties of the layers were discussed. All RF sputtered Zn0.8Mg0.2O (ZMO) and ZnO:Ga were coated on SnS as buffer and window layers respectively. The band offsets at the SnO2/SnS and ZMO/SnS heterojunctions were evaluated using X-ray photoelectron spectroscopy measurements. The conduction band (ΔEc) and valence band (ΔEv) discontinuities were determined as approximately 1.0 eV and 3.5 eV for SnO2/SnS and 0.4 eV and 1.7 eV for ZMO/SnS junction. The related energy band diagram was constructed and the results discussed.