From SnS and PbS towards complex sulfosalts: thin film growth and properties

Polycrystalline thin films of Sn1−xPbxS (0 ≤ x ≤ 0.5) were grown by multi-beam hot-wall deposition using SnS and PbS as source materials. Employing evaporation temperatures of TPbS ≈ 680 °C and TSnS ≈ 600 °C dendritic thin film growth appears due to high supersaturation at the substrate surface (TSubstrate ≈ 240…375 °C). Therefore, both evaporation temperatures were lowered to TPbS ≈ 600 °C and TSnS ≈ 540 °C. Calculated and measured thin film compositions agree very well. The variation of the deposition time exhibits linear thin film growth. At the very beginning of film growth a well-distinct texture can be observed. If the growth proceeds (t > 5 min) this texture disappears. As determined by transmission UV-Vis spectroscopy all Sn1−xPbxS films show a direct allowed transition which bandgap energy increases with increasing x and an indirect allowed transition which bandgap energy decreases with increasing lead content. Decreasing film thickness leads to an increase of both bandgap energies. The obtained results were discussed with respect to a possible application as absorber material in solar cells. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)