No abstract

Performances of dye-sensitized solar cells prepared from nanoporous TiO 2 films with different TiO 2 nanoparticle preparation methods and different annealing temperatures are studied with various film thicknesses. The results show that the solar cells prepared at higher annealing temperatures have higher energy conversion efficiencies. Regarding film thickness, thin film electrode solar cells annealed at low-temperature show comparable efficiencies with those of the cells annealed at high temperature. The difference of the efficiency between the cells with the film annealed at different temperatures increases with the film thickness. To explain the observations, the surface area of the films, the amount of the adsorbed dye, and the diffusion coefficient and lifetime of electrons are measured. The amount of adsorbed dye per unit area is found to be independent of annealing temperature, while the diffusion coefficient and lifetime increase with the temperature. With trapping models, the measured increases of the diffusion coefficient with annealing temperature are interpreted with the change of the charge-trap density and neck growth between particles, which are suggested by transmission electron microscope and surface area measurements of the films. Diffusion lengths of electrons for each solar cell estimated from the diffusion coefficient and lifetime increase with annealing temperature. From the comparison between the short circuit currents of the solar cells with the diffusion lengths, it is concluded that the higher efficiencies of the solar cells prepared from high-temperature annealed films are attributed to their longer diffusion lengths of electrons.

Wrapped up but still active: A platinum nanoparticle that is 2.2 nm in diameter and not coated by any stabilizing agent can be encapsulated in a hollow carbon shell 30–40 nm in diameter with a micro‐ to nanoporous wall structure (see picture). This encapsulated nanoparticle acts as an efficient and recyclable heterogeneous catalyst for various liquid‐phase hydrogenation reactions.

Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.