A Newly Designed Nb-Doped TiO2/Al-Doped ZnO Transparent Conducting Oxide Multi layer for Electrochemical Photoenergy Conversion Devices

We present dye-sensitized solar cells (DSSCs) employing a thermally and chemically stable Nb-doped TiO2 (NTO)/Al-doped ZnO (AZO) multilayer transparent conducting oxide (TCO) thin film. The NTO overlayer was found to block oxygen diffusion into AZO during the air-annealing process for the fabrication process of the DSSCs, thereby exhibiting good thermal stability in electrical conductivity of the multilayer TCO. Moreover, the NTO overlayer suppressed the formation of Zn2+-dye aggregates at the surface of the AZO. The DSSC employing this multilayer TCO showed a photon to electron conversion efficiency of 3.8% compared to 1.9% for the cell employing the AZO single layer. The optical transmittance and charge transport properties that were measured using electrochemical impedance spectroscopy demonstrate that NTO/AZO is a promising TCO for large scale DSSCs.