Elemental sulfur-based electrodeposition of indium sulfide films

We report research on electrodeposition of indium sulfide films, with In
₂
S
₃
a less hazardous alternative to CdS buffer layers in solar cells. Numerous organic and aqueous/organic electrolytes of InCl
₃
, NaCl, and elemental sulfur were investigated, including several glycols and amides. Temperatures ranged from 80-170°C, and deposition voltages from -0.6 to -1.2 V (Ag/AgCl with organic filling solution). Substrates included indium tin oxide-on-glass, molybdenum, and titanium, with indium or graphite anodes. Rapid stirring was used. Deposition was sluggish in all baths. Uniformity and adherence were only moderate, with irregular coverage and cracking-and-flaking sometimes evident. The best baths were ethylene glycol or 1, 2-propanediol-based, with golden-yellow films, nominally In
₂
S
_3-x
O
_x
, depositing typically heavier around the substrate edges. With low temperatures and/or large currents, brown films more rich in indium sometimes formed. Cyclic voltammetry elucidated onset potentials, secondary reactions, and photoactivity, with the greatest anodic photocurrents arising from In
₂
S
₃
's n-type conductivity occurring with mixed ethylene glycol/propionic acid/water baths. Scanning electron microscope photographs indicated a compact small grain microstructure for yellow films. Energy dispersive X-ray analysis and photoelectron spectroscopy data indicate up to 15% oxygen content.