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.

TiO 2 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.

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 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.

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][4][5][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 ] On the other hand, one-dimensional (1D) nanostructures such as nanowires and nanotubes offer superior electron transport pathways and improved light scattering, but they suffer from very low surface area (roughly an order of magnitude lower than nanoparticle fi lms). [ 10 , 11 ] In conjunction with these efforts, 3D inverse opal (IO) nanostructures possessing highly ordered interconnected shells, high porosity ( ∼ 75%), and photonic crystal light localization have shown to be promising in photovoltaics and PEC cells. [12][13][14][15][16][17][18][19][20] While the fabrication scalability of these photoanodes has been established using a combination of a simple doctor blading method and atomic layer deposition (ALD), [ 19 ] the highest effi ciencies reported so far still fall behind those of mesoporous nanoparticle fi lms, mainly because of the surface area disparity. Highest PEC effi ciencies of 3.47% and 2.7% have been reported for dye-sensitized and quantum dot (QD)-sensitized unmodifi ed TiO 2 IO photoanodes, respectively. [ 12 , 16 ] It is envisaged that the promise of these 3D photoanodes can be further achieved when a substantial proportion of the pore volume is carefully exploited to resolve the issue of surface area shortage.In this Communication, we demonstrate a novel nanoarchitecture consisting of 3D ordered hierarchical nanobushes, using TiO 2 IOs as the host template for the facile solution growth of ZnO nanowire networks. The TiO 2 IO/ZnO nanowire hybrid nanostructure is sensitized with CdS QDs and investigated as a PEC photoanode. The key idea here is to couple the ZnO nanowires with the TiO 2 IO to achieve higher sensitizer loading and larger contact interface areas with the electrolyte, and enhance light scattering. PEC performance measurements of the nanobush photoanode do indeed show ...