Study of wide bandgap n-type CdS window layers for thin-film solar cells

Chemical bath deposition is used for deposition of pure and Al-doped CdS layers on glass substrates at 80 °C. Thin films were prepared from a solution containing sodium sulphide, cadmium nitrate, aluminium chloride, sodium hydroxide used, respectively, as source for sulphur, cadmium, aluminium and as complexing agent. Films were characterised for structure, conductivity type and optical properties using XRD, hot probe technique and UV–VIS, respectively. Characterisation showed CdS thin films were either hexagonal or cubic, oriented along H(002) or C(111), respectively, and transparency ranged 40 to 80% in 300–1000 nm. With increasing doping concentration, absorbance raised and transmittance started falling. Films showed absorption coefficient increased with concentration of aluminium dopants, with energy bandgaps (2.76, 2.55, 2.47, 2.64, and 2.59 eV) for the as-deposited and Al-doped CdS films varying with Al (1, 2.5, 5, and 10) mol%. All thin films showed n-type conductivity, suggesting CdS a better widow layer for solar cells. Graphical abstract