Transparent Conductive Oxides

Abstract

The dielectric functions and optical constants of various transparent conductive oxide (TCO ) materials, which have been incorporated into solar cell devices, are summarized. The TCO materials described here include In₂O₃:Sn (ITO), In₂O₃:H, InZnO, SnO₂:F, TiO₂, and ZnO:Al (or Ga). Oxide layers such as MoO_x, NiO, and WO₃ are often employed to improve electronic properties at semiconductor interfaces and the optical data of these TCO layers are also described. In conventional solar cells, the free carrier absorption that occurs within the TCO layers reduces the photocurrent largely, and the characterization of the parasitic absorption within the solar cell is quite important. Accordingly, for ITO and doped ZnO layers, the variation of the dielectric function with carrier concentration is presented. Since non-doped TCO layers are widely employed as high-resistive buffer layers, the dielectric functions of non-doped In₂O₃, SnO₂ and ZnO are also described. It is established in this chapter that all the TCO dielectric functions in the whole near-infrared/visible/ultraviolet region (1–5 eV) can be parameterized by the combined use of the Tauc-Lorentz and Drude models. For the modeling with the Tauc-Lorentz model, several transition peaks are assumed in the ultraviolet region to describe the interband transition above the band gap. In this chapter, the parameterization results for all the TCO materials are summarized, together with the tabulated optical constants.