Transmittance optimized nb-doped TiO₂/Sn-doped In ₂O₃ multilayered photoelectrodes for dye-sensitized solar cells

We adopt a compact TiO₂ (c-TiO₂) layer on Nb-doped TiO₂ (NTO)/Sn-doped indium oxide (ITO) multilayered electrodes, which are transparent conducting oxide (TCO) electrodes, to improve their transmittance for high-efficiency dye-sensitized solar cells (DSSCs). An NTO layer was deposited on ITO by pulsed laser deposition (PLD) and then a c-TiO₂ layer was deposited on the NTO/ITO multilayer by spin-coating a sol. The transmittance spectrum of the c-TiO₂/NTO/ITO multilayered photoelectrodes varied with the thickness of TiO₂. The short circuit current and energy conversion efficiency of the photoelectrodes also varied with the thickness of the c-TiO₂ layer, which is similar behavior to the integrated value of the transmittance in the wavelength range from 500 to 600 nm. Finally, the DSSC employing the 160 nm-thick c-TiO₂ layer exhibited the most improved energy conversion efficiency, compared to the DSSC without the c-TiO₂ layer. Our results demonstrate that the unfavorable optical properties of TCO, e.g. NTO, for DSSCs can be enhanced by the formation of an additional thin layer, e.g. c-TiO₂.