IMPROVEMENT OF ELECTRIC PROPERTIES OF ELECTRODEPOSITED CdTe FOR SOLAR CELL BY MICROSTRUCTURE CONTROL

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CdTe is a promisng material for solar cell applications. We demonstrated that aqueous basic ammoniacal electrolytes, instead of traditional acidic sulfate lectrolytes, are suitable for electrodeposition of uniform p-type CdTe layers. However, the resistivity of the p-type CdTe was grater than that of the n-type CdTe from the acidic bath. The grain sizes of as prepared CdTe layers from basic electrolytes are smaller than those from acidic media. To improve the electric properties of electrodeposited CdTe, it may be effective to obtain CdTe with larger grains. Electrodeposition at higher temperature is a plausible way for this purpose. In the ammoniacal basic electrolyte, however, azeotropy occurs at 348 K. Therefore, we developed an autoclave-type vessel and employed a galvanic contact deposition method. CdTe layers were obtained at a temperature range from 363 K to 423 K. The rise in the deposition temperatures slightly increased the Cd contents and mean crystallite size of CdTe. A near stoichiometric CdTe layer with mean crystallite size of 19 nm was obtained at 393 K.The effect of chloride ions was investigated. The asdeposited CdTe layer had an n-type conduction, suggesting that chloride ions in the electrolyte became incorporated into the CdTe layer and formed the donor level.The effect of thermal treatment on the grain size of CdTe was examined. CdTe layer with mean crystallite size of 33 nm was obtained by at 673 K for 30 min. The energy conversion efficiency of the p-CdTe/ n-CdS heterojunction solar cell prepared by electrodeposition and the thermal treatment was 1.8 %.