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Aligned photoelectrodes have been intensively investigated due to their prominent electron dynamics, but their device performance has been limited by their small surface area. Here, we synthesized vertically aligned TiO2nanoarchitectures with large internal surface areas and open channels of pores via pulsed laser deposition (PLD) and investigated the effects of the deposition conditions and the postannealing on the formation and properties of nanoarchitecture photoelectrodes for dye-sensitized solar cells. Increasing the oxygen working pressure increases the porosity of the TiO2film and decreases the amount of deposited materials resulting in an optimized oxygen working pressure of 100 mTorr. The as-deposited films were amorphous and crystallized to the pure anatase phase after annealing at 350 °C or higher. Annealing at higher temperatures resulted in larger grain sizes and larger electron diffusion coefficients. As a result of the compromise between the surface area and crystallinity (or diffusion coefficient), the TiO2film that was annealed at 450 °C exhibited optimal solar cell performance. We showed that the optimized PLD-TiO2photoelectrodes (i.e., deposited at 100 mTorr and annealed at 450 °C) exhibited higher solar conversion efficiencies than the conventional nanoparticle films owing to their larger short-circuit photocurrent density resulting from the larger surface area and slower charge recombination. Our results show that PLD is a promising technique for preparing various aligned functional nanomaterials with high surface area for the improved device performance.

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.

Mn2+-doped Zn2SiO4phosphors with nanoellipsoid or nanowire morphologies were synthesized at low temperature <200 °C by a hydrothermal method without any surfactants. The morphologies of the phosphors were easily tailored by varying the amount of hydroxide ions in the precursor solution before the hydrothermal reaction. Absolute ethanol was used as a solvent instead of distilled water to explore the effects of hydroxide ions on the morphology and crystal structure. We adjusted the amount of hydroxide ions by changing the pH of the precursor solution. Sheaves of powders with an ellipsoid shape were synthesized at low pH values of 7 and 9, at which only a few hydroxide ions were present, whereas powders with a nanowire shape were produced at a high pH of 11, at which many hydroxide ions were present. In addition to its morphology, the hydroxide ions also affect the crystal structure of the synthesized powder. Whereas a Zn2SiO4phase with a willemite structure was formed at pH 7 and 9, a Zn4Si2O7(OH)2·H2O phase with a hemimorphite structure was formed at pH 11. The as-prepared powders with a willemite structure showed an intense green emission (λ ≈ 525 nm) under 254 nm excitation, whereas the as-prepared powders with a hemimorphite structure did not show any emission. However, all of the powders showed a willemite structure while retaining their original shape after annealing at 900 °C under a reducing atmosphere. The annealed sheaves of willemite with an ellipsoid shape showed a more intense green emission with a longer decay time than the phase-transformed willemite nanowires. These results were discussed in terms of the surface defects and dopant concentration.

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 TiO2layer 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 TiO2layer, 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 TiO2compact layer in highly efficient DSSCs.

In this study, we present a thermally stable multilayered transparent conducting oxide (TCO) functionalized for dye-sensitized solar cells (DSSCs). Nb-doped TiO2(NTO) layers deposited on conventional Sn-doped In2O3(ITO) substrates using pulsed laser deposition (PLD) enhanced the optical-to-electrical conversion efficiency of the DSSCs by as much as 17% compared to that of bare ITO-based DSSCs. The electrical properties and J−Vcharacteristics of the multilayered NTO/ITO films showed that the improved cell performance was due to the facilitated charge injection from TiO2to ITO that resulted from the formation of an ohmic contact with ITO, as well as the conserved high conductivity of ITO after the oxidizing annealing process. Moreover, the NTO/ITO-based DSSC exhibited higher efficiency than a F-doped SnO2(FTO)-based one, which demonstrates that optimization of multilayered NTO-based TCOs is a realistic approach for achieving highly efficient photoenergy conversion devices.