Nb-doped tio ₂: A new compact layer material for TiO ₂ dye-sensitized solar cells

A Nb-doped TiO ₂ (NTO) thin film was deposited on a fluorine-doped tin oxide (FTO) electrode by pulsed laser deposition (PLD) and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. On the basis of the investigation of the dark current, open circuit voltage (V _oc) decay, current-voltage (/- V) characteristics, and electrochemical impedance spectra (EIS), it was found that the NTO layer functioned as both a blocking layer and an ancillary transparent conducting oxide (TCO) layer. As a blocking layer, the NTO layer suppressed the charge recombination from TCO to the electrolyte. In addition, as an ancillary TCO layer, the NTO layer reduced the interfacial resistance between the TiO ₂ layer and TCO by forming an ohmic contact. As a result, the overall energy conversion efficiency of the DSSC incorporating the NTO layer was enhanced by 21.2% compared to that with the bare FTO substrate and 4.1% compared to that with the undoped TiO ₂ layer, owing to the enhanced charge transfer and collection characteristics of the NTO layer. Our results demonstrated that NTO is a promising alternative to the conventional TiO ₂ compact layer in highly efficient DSSCs.