Recently, dye-sensitized solar cells (DSC) have attracted much attention with their low production costs of electricity and relatively high energy-conversion efficiencies. [1][2][3][4] One of the key elements in DSC is the nanoporous TiO 2 electrode, which transfers the electrons from the dye molecules to the transparent conductive-oxide (TCO) electrode and concurrently allows the electrolytes to diffuse to the anchored dyes. Typically, nanoparticles are utilized for the fabrication of the nanoporous TiO 2 layers on the TCO to obtain high surface areas and generate nanopored structures. [1,5,6] In this TiO 2 layer derived from nanoparticles, however, the electrons produced from the dye molecules have to pass through numerous grain boundaries in order to reach the TCO, and the transport of the electrolytes is not efficient due to the irregularity of the pores generated. To this point, the tailoring of TiO 2 nanostructures is a crucial aspect of increasing the current photovoltaic-conversion efficiency of DSC. [7][8][9][10][11][12][13][14][15][16][17][18][19] For the formation of an efficient DSC, a high surface area is prime and essential for the TiO 2 layer to load large amounts of dye molecules that will generate electrons by absorbing sun light. Second, the pores formed in the TiO 2 layer must be sufficiently large in size with excellent mutual connectivity for the efficient diffusion of electrolytes. Third, the defect level and the number of grain boundaries must be minimized to suppress the loss of electrons by recombination or back reaction. In general, however, these factors are not compatible with one another. For example, upon decreasing the size of the TiO 2 nanoparticles, the surface area of the fabricated nanoporous TiO 2 film is increased, and thus more dye molecules can be adsorbed. However, the average pore size is decreased simultaneously, and more defect sites and grain boundaries can be generated in the fabricated TiO 2 film. Therefore, it has been reported that the optimum particle size of TiO 2 has to be in the range of 12-20 nm. [5,6,[20][21][22] In this work, we designed a novel hierarchical pore structure that provides high surface area and large pore size at the same time. That is, nanoporous TiO 2 spheres with high surface area were synthesized and utilized to form the nanoporous TiO 2 electrode. As a result, two kinds of pores were successfully formed in the TiO 2 layer. Tiny internal pores were formed inside the TiO 2 sphere, while large external pores were generated by formation of the interstitial voids among the spherical structures. The large external pores can be used as a ''highway'' for electrolyte diffusion, as shown in Scheme 1. Therefore, it is expected that this porous spherical structure can provide both great adsorption of the dye molecules and efficient electrolyte diffusion at the same time.Sub-micrometer-sized TiO 2 spheres have often been prepared by sol-gel methods controlling the hydrolysis and condensation reactions, and their crystallized structures were formed by su...

Submicron-sized monodispersed TiO 2 spheres (SPs) with high porosity were synthesized by a controlled hydrolysis of titanium tetraisopropoxide (TTIP) and subsequent hydrothermal treatment at 230 C. By adjusting the ratio of TTIP to water (the r-factor) in the hydrolysis reaction, the diameters of SPs were selectively controlled to 260, 350, 450, 560, 800, and 980 nm. The prepared SPs in the pure anatase phase were highly porous structures with crystallite sizes of $15 nm and surface areas of 101-121 m 2 g À1 . The synthesized nanoporous SPs in different sizes were then applied as the lightscattering layer (LSL) of dye-sensitized solar cells (DSCs) for efficient utilization of solar spectrum, and the size-dependent light-scattering effects of those SPs were systematically investigated. The 450 nm sized SP (SP450) provided the highest light-scattering efficiency among those in the 260-800 nm range. Relatively higher efficiency is caused by the characteristic light-scattering effect based on its unique diameter and also by the photonic reflection effect originating from its size-uniformity and long-range ordering. As a result the photovoltaic conversion efficiency (h) of DSC was improved from 6.92 to 9.04% with introducing the nanoporous SP450 as LSL.

The efficient generation of dihydrogen on molecularly modified p-Si(111) has remained a challenge due to the low barrier heights observed on such surfaces. The band-edge and barrier height challenge is a primary obstruction to progress in the area of integration of molecular H2 electrocatalysts with silicon photoelectrodes. In this work, we demonstrate that an optimal combination of organic passivating agent and inorganic metal oxide leads to H2 evolution at photovoltages positive of RHE. Modulation of the passivating R group [CH3 → Ph → Naph → Anth → Ph(OMe)2] improves both the band-edge position and ΔV (Vonset - VJmax). Subsequent atomic layer deposition (ALD) of Al2O3 or TiO2 along with ALD-Pt deposition results in to our knowledge the first example of a positive H2 operating potential on molecularly modified Si(111). Mott-Schottky analyses reveal that the flat-band potential of the stable Ph(OMe)2 surface approaches that of the native (but unstable) hydride-terminated surface. The series resistance is diminished by the methoxy functional groups on the phenyl unit, due to its chemical and electronic connectivity with the TiO2 layer. Overall, judicious choice of the R group in conjunction with TiO2|Pt effects H2 generation on p-Si(111) photoelectrodes (Voc = 207 ± 5.2 mV; Jsc = -21.7 mA/cm(2); ff = 0.22; ηH2 = 0.99%). These results provide a viable hybrid strategy toward the operation of catalysts on molecularly modified p-Si(111).

Long-range ordered cubic mesoporous TiO 2 films with 300 nm thickness were fabricated on fluorine-doped tin oxide (FTO) substrate by evaporation-induced self-assembly (EISA) process using F127 as a structure-directing agent. The prepared mesoporous TiO 2 film (Meso-TiO 2) was applied as an interfacial layer between the nanocrystalline TiO 2 film (NC-TiO 2) and the FTO electrode in the dye-sensitized solar cell (DSSC). The introduction of Meso-TiO 2 increased J sc from 12.3 to 14.5 mA/cm (2), and V oc by 55 mV, whereas there was no appreciable change in the fill factor (FF). As a result, the photovoltaic conversion efficiency ( eta) was improved by 30.0% from 5.77% to 7.48%. Notably, introduction of Meso-TiO 2 increased the transmittance of visible light through the FTO glass by 23% as a result of its excellent antireflective role. Thus the increased transmittance was a key factor in enhancing the photovoltaic conversion efficiency. In addition, the presence of interfacial Meso-TiO 2 provided excellent adhesion between the FTO and main TiO 2 layer, and suppressed the back-transport reaction by blocking direct contact between the electrolyte and FTO electrode.

We report the fabrication of a {semiconductor}|{metal oxide}|{molecular catalyst} construct for the photogeneration of dihydrogen (H2) under illumination, including band-edge modulation of the semiconductor electrode depending on the identity of Si(111)-R and the metal oxide. Briefly, a synergistic band-edge modulation is observed upon (i) the introduction of a p-Si|n-AZO heterojunction and (ii) introduction of an organic dimethoxyphenyl (diMeOPh) group at the heterojunction interface; the AZO also serves as a transparent and conductive conduit, which was capped with an ultrathin layer (20 Å) of amorphous TiO2 for stability. A phosphonate-appended PNP ligand and its Ni complex were then adsorbed to the p/n heterojunction for photoelectrochemical H2 generation (figures of merit: Vonset ≈ + 0.03 V vs NHE, Jmax ≈ 8 mA cm(-2) at 60 mM TsOH).