The effect of heteropolyacids and isopolyacids on the properties of chemically bath deposited CdS thin films

The deposition of US films on ITO/glass substrates from a chemical bath containing cadmium acetate, ammonia, ammonium acetate and thiourea has been carried out with and without small amounts of heteropolyacids (HPA) (phosphotungstic acid (PTA): H-3[PW12O40], silicotungstic acid (STA): H-4[SiW12O40], phosphomolybdic acid (PMA): H-3[PMo12O40]) and isopolyacids (IPA) (tungstic acid TA): H2WO4 and molybdic acid (MA): H2MoO4) for different deposition times. The chemical, morphological, structural and optical properties of the films have been determined. The composition in sulphur and in cadmium of the films' surface and volume was determined for various HPA and IPA used in the deposition bath. The HPA and IPA which give the thickest film with the biggest grain size were deduced. The optical transmission at 400 nm of US films deposited with STA at short time (20 min) (50%) is higher than those of US deposited at longer time (6 h) (7%). The optical transmission of US deposited with STA at short time is higher (50%) than that of US deposited without STA (20%). The performances of heterojunctions CdS/CdTe solar cells fabricated from US films deposited with and without STA and CdTe films deposited without STA have been determined. It was shown that the CdS/CdTe heterojunction solar cells fabricated from US films deposited with STA exhibited better photon collection efficiency and solar cell efficiency (eta = 6%) than CdS/CdTe heterojunction solar cells fabricated from US films deposited without STA (eta = 3.3%). (C) 2001 Elsevier Science B.V. All rights reserved.