Hybrid photovoltaic structures based on polymer/chemically grown cadmium selenide films: effect of silicotungstic acid on the junction properties

Thin cadmium selenide layers were deposited by chemical bath deposition (CB D) on various substrates: glass, gold, indium tin oxide (ITO), and poly(3-m ethylthiophene) (PMeT), an organic conducting polymer. In all cases, CdSe a dhered strongly to the substrate. X-ray diffraction, scanning electron micr oscopy, and optical transmission revealed an effect of the substrate nature upon the structural and optical properties of CdSe films. Because CdSe is an n-type semiconductor and PMeT either a p-type semiconductor or a quasi-m etallic conductor, attention was focused on the hybrid organic-inorganic ph otovoltaic junctions, which result either from CdSe chemical bath depositio n on PMeT or, conversely, from PMeT electropolymerization on CBD CdSe. In t he former case, a p-n type junction was obtained, whereas, in the latter ca se, a Schottky-type junction was obtained. The nonoptimized photovoltaic en ergy conversion efficiency of these junctions under 56 mW cm(-2) white ligh t from a Xenon lamp were 0.03 and 1.3%, respectively. When CdSe was deposit ed in the presence of silicotungstic acid (STA) in the chemical bath, local ized energy levels were created in the forbidden band of CdSe, which improv ed the optical properties of the thin films, and hence, the energy conversi on efficiency, which increased up to 2.7% for the Schottky-type photovoltai c organic-inorganic PMeT/CdSe(STA) photovoltaic junction. (C) 2000 Elsevier Science Ltd. All rights reserved.