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

镉镉是一种很有前途的太阳能电池材料。我们证明了用碱性水溶液代替传统的酸性硫酸盐电解液更适合于电沉积均匀的p型CdTe层。但在酸性条件下，p型CdTe的电阻率大于n型的。在碱性电解液中制备的CdTe层的颗粒尺寸比在酸性介质中制备的要小。为了改善电沉积的CdTe的电学性能，获得更大颗粒的CdTe可能是有效的。在更高的温度下进行电沉积是一种可行的方法。然而，在氨性碱性电解液中，共沸点发生在348K，因此，我们开发了一种高压釜式容器，并采用了电偶接触沉积方法。在363K~423K的温度范围内获得了CdTe层，沉积温度的升高略微增加了Cd的含量和平均晶体尺寸。在393K下获得了平均尺寸为19 nm的近化学计量比的CdTe层，并考察了氯离子的影响。沉积后的CdTe层具有n型电导，表明电解液中的氯离子进入到了CdTe层中，形成了施主能级。在673K下保温30min，得到了平均晶粒尺寸为33 nm的CdTe薄膜。电沉积和热处理制备的p-CdTe/n-CDS异质结太阳电池的能量转换效率为1.8%。

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 %.