Preparation of crystalline CdSe particles by chemical bath deposition
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Preparation of crystalline CdSe particles by chemical bath deposition Osamu Yamamoto and Tadashi Sasamoto Department of Applied Chemistry, Kanagawa Institute of Technology, 1030 Shimo-ogino, Atsugi-shi 243-02, Japan
Michio Inagaki Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan (Received 18 October 1997; accepted 23 February 1998)
Crystalline CdSe particles were prepared by keeping the precursor solutions at temperatures above 60 ±C. It was essential to use sodium sulfite as a stabilizing agent for selenium ions and sodium dicarboxylate as a complexing agent for cadmium in the precursor solution. The principal crystalline phase of the samples obtained at 60 ±C was a cubic zincblende-type phase, but those prepared at 80 ±C coexisted with a hexagonal wurtzite-type phase. The ratio of cadmium to selenium in the samples decreased with an increase of the concentration of selenourea in the precursor solutions, irrespective of the kind of complex agents and the keeping time of the precursor solutions. The band-gap energy of CdSe with an atomic ratio (CdySe) of 1 showed a value of 1.74 eV, but that with the ratio of 2.3 gave a slightly smaller value of 1.42 eV.
I. INTRODUCTION
II. EXPERIMENTAL
The solar cells constructed with multilayers have recently been studied to obtain high efficiency conversion of solar energy, in order to solve energy and environment problems.1– 4 The structure of the multilayer cells has been proposed to be constructed with four layers of transparent conductive metal oxide/metal sulfide/metal selenide or metal telluride/metal, such as In2 O3 –SnO2yCdSyCdSeyMo.5,6 In the preparation of these thin films, CdS thin films have been synthesized by an electrochemical process and chemical bath deposition (CBD),7–11 whereas the preparation of CdSe thin films by an electrochemical process was reported by Windheim et al.,12 but the CdSe thin films by CBD have scarcely been reported, probably because of either precipitation of SeO2 particles due to the extreme sensitivity of selenium ions to water or no formation of CdSe due to the low reactivity between cadmium ions and selenium ions. In order to prepare crystalline CdSe by CBD, the use of complex agents for both cadmium and selenium ions seem to be important, particularly stabilization of selenium ions to avoid the formation of SeO2 being essential. As the first step of the research in the present work for preparing CdSe films, the powder of CdSe is successfully prepared by CBD using complex agents for both cadmium and selenium ions. The preparation conditions of CdSe particles are described and then the crystal structure, the chemical composition, and the band-gap energy of the obtained samples are discussed.
A. Preparation of CdSe particles
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J. Mater. Res., Vol. 13, No. 12, Dec 1998
In Fig. 1, the preparation procedure of the CdSe precursor solution is shown as a flow sheet. Cadmium chloride (CdCl2 ) and selenourea [SeC(NH2 )2 , SeU] were used as the raw materials. S
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