SnO films were fabricated at low temperature (60–220 °C) by rf magnetron sputtering. X-ray diffractometry and scanning electron microscopy revealed that the films contained polycrystalline SnO nanorods several tens of nanometers long and SnO2 was present in films grown at ≥180 °C, suggesting the decomposition of SnO by disproportionation. Photoacoustic and transmittance spectroscopies revealed an indirect fundamental gap of 0.7 eV and a direct gap of ∼2.9 eV, respectively. Thermoelectric and Hall measurements both indicated that films grown at ≤180 °C exhibited p-type conductivity. The electrical and optical properties of the films are rationalized by considering the structural changes caused by disproportionation.

Cu2ZnSnS4 thin films containing grains grown using Sn vapor transport (TVT) were investigated. Structural characterization revealed that the grain sizes were equal to or larger than the film thickness (1–4 µm) and significantly larger than those in the case of growth without TVT (60 nm). Furthermore, no phase separation was detected. Photothermal diffraction spectroscopy revealed that the optical absorption coefficient was very low in the subgap region, 7×101 cm-1, suggesting the suppression of defect formation. Finally, a TVT-processed thin film was used as an absorber in a solar cell, and a conversion efficiency of 6.9% was achieved.

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