Nb-doped TiO2 Thin Films Research Articles

Electronic Manifestation of Cation‐Vacancy‐Induced Magnetic Moments in a Transparent Oxide Semiconductor: Anatase Nb:TiO2

Nb-doped anatase TiO2 thin films grown by pulsed-laser deposition show Kondo scattering in elctronic-transport measurements, providing evidence for the formation of magnetic moments. The origin of magnetism is attributed to cation (Ti) vacancies, confirmed by X-ray absorption spectroscopy and first-principle calculations. The Ti vacancies are controlled by oxygen partial pressure during growth.

Nb-Doped TiO2: A New Compact Layer Material for TiO2 Dye-Sensitized Solar Cells

A Nb-doped TiO2 (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 (Voc) decay, current−voltage (I−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 TiO2 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 TiO2 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 TiO2 compact layer in highly efficient DSSCs.

Non-adiabatic small polaron hopping conduction in Nb-doped TiO2 thin film

Abstract Transport properties of Nb-doped titanium oxide (TiO 2 ) thin film, obtained by a RF sputtering technique, have been investigated by means of the electrical conductivity and the Seebeck coefficient as a function of temperature (13–425 K). At high temperatures ( T >325 K), temperature dependent behaviors of the electrical conductivity and the Seebeck coefficient confirm that the transport mechanism is the non-adiabatic small polaron hopping type. An excellent agreement between the theoretical and the experimental values of non-adiabatic polaron hopping energy ( W H ≈0.3 eV) is obtained. The conductivity follows the Mott's variable range hopping conduction (VRH) at the temperature range of 200–325 K, while it exhibits a temperature-independent behavior at low temperatures ( T

Improved Performance of Organic Light-Emitting Device with Anatase TiO2 Anode

An organic light-emitting device (OLED) with a Nb-doped anatase TiO2 thin film on a LaAlO3 substrate as an anode shows higher performance than OLEDs with a rutile TiO2 anode. The OLED structure is TiO2/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/N,N'-di-[(1-naphthalenyl)-N,N'-diphenyl]-(1,1'-biphenyl)-4,4'-diamine (α-NPD)/tris(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al. The maximum luminance is about 3200 cd/m2 at 20 V, and the current efficiency is approximately 2–3 cd/A, which is comparable to that of a reference OLED with an Sn-doped In2O3 (ITO) anode. We speculate that the improvement of the OLED performance comes from the low resistivity with a relatively low electron density of anatase TiO2.

Optical properties of TiO2 thin films estimated by photothermal deflection spectroscopy

The optical properties of Nb doped TiO2 thin films have been investigated by using the photothermal deflection spectroscopy. The below-gap absorption of amorphous and microcrystalline TiO2 thin films is observed. The absorption coefficient in the below-gap region in microcrystalline TiO2 film decreased with thermal annealing at ∼650 °C. The origin of the below-gap absorption is discussed on the basis of the structural information.