In this review, we will introduce our recent results concerning the correlation between molecular orientation/ crystallinity and external quantum efficiency. We have examined the structural effects of Zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic hetero-junction photovoltaic (OPV) cells [ITO/Zn(OEP)/C60/Al], and investigated what exactly causes the improvement of EQE. When the structure of Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of ca. 35% for previously reported OPV cells using buffer materials [P. Peumans and S.R. Forrest, Appl. Phys. Lett. 79 126 (2001)]. Crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE under illumination of the photo-absorption band due to the IMCT excitons.
Flexible, transparent conductive film was successfully fabricated by embedding Au nanofin arrays into a polymer film through nanocoating lithography technique. The film with Au nanofin arrays has an anisotropic conductivity parallel to the Au nanofin direction. Its transparency and sheet resistivity were 81% in visible wavelength range and 43 Ω/sq., respectively, which are comparable to those of a commercial ITO sheet. Moreover, Au nanofin film has high flexibility with a curvature radius of 3.5 mm. Au nanofin film will be applied to electrodes for photo-electron devices such as solar cells, organic light emitting diodes, and see-through flexible displays.
In the last few years, the number of publication on dealloyed nanoporous metals increases very quickly, which will attracted more and more attentions in the future. In the paper, we focus on the recent progresses of various nanoporous metals, alloys and related composites, including the fabrication and microstructure. We discuss their physical properties and applications in the fields of heterogeneous catalysis, electrocatalysis, and energy storage.
To improve the photocurrent of a DSSC by enhancing the metal-to-ligand charge transfer (MLCT) transition of a dye, Ag nanoparticles with a surface modulator were inserted into a TiO2 nanoporous film using a colloidal solution. The photoelectric conversion efficiency of the DSSC is improved by a strong electromagnetic field (often called the “optical near field”) generated by a localized surface plasmon of modified Ag nanoparticles.
The on-board storage of hydrogen in motor-vehicles is one of the most critical issues for the realization of a “low-carbon” future. Hydrogen should be stored in various materials through reversible sorption processes or via chemical reactions. Many candidates have been proposed for the storage material and these have been both experimentally and theoretically investigated. Sophisticated calculation methods and powerful computer resources have allowed nanoscale materials to be considered and examined and for useful information, such as that concerning the adsorption sites, binding energies, diffusion paths, and so on, to be obtained. Therefore, computational materials science has recently been driving one of the most exciting interdisciplinary sciences in terms of environmental concerns. In the present study, we showed that theoretical calculations which can be used to understand the properties of nanomaterials and to design novel structures with desirable functions.
Commercialization of polymer electrolyte fuel cells is starting for small size co-generation systems “Enefarm” and fuel cell vehicles. Presently, Pt/C is used for electrocatalyst. In order to move real commercialization, nonprecious metal electrocatalyst is required because of the limit of natural resources and cost problem. We focused on the 4th and 5th transition metal compounds as a fuel cell cathode catalyst because of their stability in acidic media and their activity for oxygen reaction as photoelectrocatalysts. The 4th and 5th transition metal oxides made from carbonitrides and phthalocyanine showed high onset potential for the oxygen reduction reaction. The oxygen defect would be essential to show high catalytic activity for these materials.
After the commercialization of the Li-ion battery with carbon anode, the research for cathode active materials has concentrated on lithium containing first-row transition-metal oxides with 4V class high electromotive force, because it can serve as Li source to a carbonaceous anode. However, all 4V-class rechargeable cathodes, LiCoO2, LiNiO2, and LiMn2O4, have the essential problems of safety, cost and environmental impact. These problems become serious, especially for the large scale cell. To solve these intrinsic problems, basic concept for advanced next generation cathode active material are proposed.