Influence of the kind and content of doped impurities on impurity-doped ZnO transparent electrode applications in thin-film solar cells

Abstract

The influence of the kind and content of doped impurity on the electrical properties and their stability as well as on the light scattering characteristics and the surface texture formation obtainable by wet-chemical etching was investigated to develop transparent conducting impurity-doped ZnO thin films suitable for transparent electrode applications in thin-film solar cells. Al-, B- and Ga-doped ZnO (AZO, BZO and GZO) thin films were prepared on glass substrates at 200°C by doping each impurity at an appropriate content to achieve lower resistivity using a pulsed laser deposition and by varying the doped Al or Ga impurity content using r.f. superimposed d.c. magnetron sputtering deposition. The difference in the resulting electrical properties and their stability (air at 85% relative humidity and 85°C) among the AZO, BZO and GZO thin films is attributed to the content of each impurity rather than the kind of impurity. In evaluations of the light scattering characteristics and the surface texture formation in a 0.1% HCl solution at 25°C, the difference in the haze value obtainable among the AZO, BZO and GZO thin films is mainly attributed to the content of each impurity doped into the films. The AZO, BZO and GZO films prepared with doped impurity contents below approximately 2at.% are suitable for transparent electrode applications in thin-film solar cells, irrespective of the kind of impurity as well as the deposition method used.