Sn(O, S)2 thin films by chemical bath deposition for Cd-free CIGS thin film solar cells

The buffer layers of tin compound semiconductor were deposited on the Cu(In, Ga)Se₂ (CIGS) substrates by chemical bath deposition. Sn(O, S)₂ films were grown in an alkaline ammonia solution by reaction of tin(IV) chloride with thiourea at the bath temperature of 70^oC. The smooth and conformal coverage films were achieved on the CIGS substrates with thickness of 20nm. The morphological and chemical properties were evaluated using scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). On the other hand, layer thickness of 90nm could be grown in an acidic solution with sodium sulfide (Na₂S) within 60min. When we applied the Sn compound thin films as the alternative buffers in thin film CIGS solar cells, the efficiency of 9.4% small area cells were achieved. This result provided the potential for the Sn(O, S)₂ films to be used as buffer or window layers in solar cell devices.