Liap Tat Su

Quantum‐Dot‐Sensitized TiO2 Inverse Opals for Photoelectrochemical Hydrogen Generation

A new nanoarchitecture photoelectrode design comprising CdS quantum-dot-sensitized, optically and electrically active TiO(2) inverse opals is developed for photoelectrochemical water splitting. The photoelectrochemical performance shows high photocurrent density (4.84 mA cm(-2) at 0 V vs. Ag/AgCl) under simulated solar-light illumination.

Photon Upconversion in Hetero‐nanostructured Photoanodes for Enhanced Near‐Infrared Light Harvesting

A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photo-electrochemical cells. By spatially coating upconversion nanoparticles and quantum dot photosensitizers onto TiO2 inverse opal, this architecture allows direct irradiation of upconversion nanoparticles to emit visible light that excites quantum dots for charge separation. Electrons are injected into TiO2 with minimal carrier losses due to continuous electron conducting interface.

TiO2 inverse-opal electrode fabricated by atomic layer deposition for dye-sensitized solar cell applications

TiO2 inverse opals (TIO) fabricated by the atomic layer deposition (ALD) technique showed a superior infiltration result when compared to those fabricated by the conventional nanoparticles-infiltration method reported in previous studies. The ALD can achieve high filling fractions of more than ca. 96% of the maximum possible infiltration by conformal filling of 288, 390 and 510 nm opals, giving rise to high quality TIO. The photoelectrochemical performances of the ALD-fabricated TIO photoanodes of different sizes are investigated systematically for the first time in dye-sensitized solar cells (DSCs). When the TIO with a size of 288 nm was used as photoanode and indoline dye as a sensitizer in DSCs, the power conversion efficiency of the cell could attain 2.22% (Air Mass 1.5). It is found that the efficiency increases with decreasing lattice size of TIO electrode due to the larger surface area for dye loading. Owing to the selective reflectivity of the inverse opal, IPCE spectra of TIO electrodes revealed a strong wavelength dependence. Strategies relating to the characteristics of selective reflection and the design of composite photoanodes to enhance the efficiency of DSCs are discussed.

Homogeneous Photosensitization of Complex TiO2 Nanostructures for Efficient Solar Energy Conversion

TiO2 nanostructures-based photoelectrochemical (PEC) cells are under worldwide attentions as the method to generate clean energy. For these devices, narrow-bandgap semiconductor photosensitizers such as CdS and CdSe are commonly used to couple with TiO2 in order to harvest the visible sunlight and to enhance the conversion efficiency. Conventional methods for depositing the photosensitizers on TiO2 such as dip coating, electrochemical deposition and chemical-vapor-deposition suffer from poor control in thickness and uniformity, and correspond to low photocurrent levels. Here we demonstrate a new method based on atomic layer deposition and ion exchange reaction (ALDIER) to achieve a highly controllable and homogeneous coating of sensitizer particles on arbitrary TiO2 substrates. PEC tests made to CdSe-sensitized TiO2 inverse opal photoanodes result in a drastically improved photocurrent level, up to ~15.7 mA/cm2 at zero bias (vs Ag/AgCl), more than double that by conventional techniques such as successive ionic layer adsorption and reaction.

A Novel Photoanode with Three‐Dimensionally, Hierarchically Ordered Nanobushes for Highly Efficient Photoelectrochemical Cells

In recent years, photoelectrochemical (PEC) cells have attracted worldwide attention as cheap alternatives to conventional devices for solar energy conversion. Crucial to the light harvesting and conversion effi ciency of a PEC cell is a nanostructured photoanode, in which the incident photons are captured, electron–hole pairs are generated, and the subsequent electron transfer takes place. [ 1 , 2 ] To realize highly effi cient PEC cells, a nanostructured photoanode should possess several favorable intrinsic characteristics, such as adequate specifi c surface area to permit high photosensitizer loading (in the case of TiO 2 ), direct electron transport pathways for long electron diffusion length, and strong light scattering to promote the light harvesting ability by confi ning the light within the cell. [ 3–6 ] It is thus highly desirable to develop a photoanode that meets all the above requirements. Towards this goal, immense efforts have been concentrated on tailoring the nanometer-scale features of photoanode materials. [ 7 ] Nanoparticle fi lms provide very high surface areas to increase the amount of sensitizer loading, but they lack direct electrical contacts and light-scattering ability. [ 8 , 9 ]

Photoluminescence phenomena of Ce3+-doped Y3Al5O12 nanophosphors

The photoluminescence phenomena of Ce3+-doped Y3Al5O12 nanophosphors synthesized by the chemical gelation were investigated and compared with bulk phosphors. The oxidation state of the cerium ions in the nanophosphors was determined to be trivalent. This is an essential characteristic of phosphor’s emission. The Stokes shift for the nanophosphors was less than the bulk phosphors, which indicates that the nanophosphors had restricted surroundings. The photoionization effect was observed for the nanophosphors where the 5d electrons were lost to the conduction band and trapped at the surface-defective sites. Another observation was the high concentration of surface defects on the nanophosphors. These surface defects were investigated using the high resolution transmission electron microscope.

Gradient inverse opal photonic crystals via spatially controlled template replication of self-assembled opals

A method of spatially controlled template filling and replication is reported herein using Knudsen diffusion-limited atomic layer deposition (ALD). Experimental and theoretical investigations based on the porous framework of self-assembled polystyrene opals further confirm the well controlled z-directional TiO2 spatial gradients paving the way for the fabrication of gradient index inverse opal photonic crystals for the first time.

Electron-phonon interactions in ce3+-doped yttrium aluminum garnet nanophosphors.

Ce 3+-doped yttrium aluminum garnet nanophosphors with sizes near 30 and 250 nm have been synthesized by using chemical gelation and solvothermal methods, respectively. The size-dependent electron-longitudinal-optical-phonon coupling is investigated by fitting measured photoluminescence spectra within the framework of the Brownian oscillator model. Results show that the coupling strength is in a decreasing order from the bulk material to the nanophosphors of much smaller sizes.

A novel non-catalytic synthesis method for zero- and two-dimensional B13C2 nanostructures

Boron carbide nanoparticles and nanoflakes represent nano-building blocks for complex hierarchical assembly of nanoscale structures that exhibit ideal mechanical robustness. These nano-building blocks were synthesized by simply changing the mixing ratio of the solid precursors to influence the saturation condition of the process. As such, the ability to tune the nanostructures of boron carbide was achieved by controlling the concentration of gaseous boron oxide in the process with no catalyst involved in the growing process. The phase of the resulting nanostructures were found to be B13C2, which is a much desired phase because its hardness of close to 60 GPa is twice as hard as B4C. Nanoflakes were found to contain high degree of (101)-type twins with their boundaries likely to pass through the center of icosahedra in the structure. Nanoflakes with twinned microstructure are anticipated as a model nanostructure and can provide opportunities to fundamentally explore their mechanistic nature since twins have the potential in inhibiting the crack propagation, leading to toughening the materials.

Cubic nanoassembly of garnet nanocrystals

A general strategy is demonstrated for achieving a cubic nanoassembly of complex oxide nanocrystals such as yttrium aluminum garnet. The synthesis route is based on the principle of surface energy minimization whilst taking advantage of the materials crystallization pathway. The results show that each nanocrystal in the ensemble is around 10 nm in size and the cubic nanoassembly stretches its dimensions to about 200 nm. Modifying the mechanism that minimizes surface energies during crystallization suggests a new route to structural changes. Doping large cations into the material system transforms the cubic nanoassemblies into single-crystal nanocubes. These approaches provide the general procedures to a template-free ordered nanostructure. They are likely to attract significant interest in a myriad of applications and provide opportunities to fundamentally explore their collective properties.