Hisatomo Yonehara

Dark and photoconductivity behavior of C60 thin films sandwiched with metal electrodes

Sandwich cells of C60 thin film with a front Al electrode reveal considerable rectifying effects and large photocurrents (quantum yields ≤54%) under air. The action spectra closely follow the optical absorption spectrum of the film. The relationship between photocurrent (Jph) and incident light intensity (Pin) changes from Jph∝(Pin)0.95±0.05 at Pin<3×10−7 W/cm2 to Jph∝(Pin)0.53±0.03 at higher Pin, suggesting that the photocurrent is controlled by the interaction of excitons with impurity sites at surface and near‐surface of C60 in the absence and presence of bimolecular recombination depending on light intensity.

Photoelectrical properties of double-layer organic solar cells using C60 and phthalocyanines

The photoelectrical properties of p-n junction organic solar cells based on C60 and phthalocyanines (mainly oxotitanium (IV) phthalocyanine (OTiPc)) were investigated. With the Al/C60/OTiPc/ITO configuration, the energy conversion efficiencies (η) are high at low incident light intensities (pin), due to the formation of a p-n junction between C60 and OTiPc, but decrease with an increase in pin. On the other hand, ITOC60OTiPcCr·Au cells are stable even under white-light illumination at high pin. It was found that the insertion of an SiO2 insulator layer between OTiPc and Cr· Au significantly enhances the short-circuit current, the open-circuit voltage and η.

Improving Charge/Discharge Properties of Radical Polymer Electrodes Influenced Strongly by Current Collector/Carbon Fiber Interface

Charge/discharge processes of organic radical batteries based on the radical polymers redox reaction are largely influenced by carbon fibers consisting in the composite electrodes to help electron transfer. To find the optimal structure of the composite electrodes, the dominant electron transfer processes were determined by ac impedance measurement of the composite electrodes. A strong correlation between the overall electron transfer resistance of the composite electrodes and the materials of the current collector suggests that the electric conduction to the current collector through the contact resistance should be crucial. It was also confirmed that the charge/discharge performance of the composite electrode was related to the overall electron transfer resistance of the composite electrode. These results indicated that the charge/discharge performance of the radical battery was dominated by the interfacial electron transfer processes at the current collector/carbon fiber interface and that the rate performance would be much improved by suitably designing the interfacial structure.

Chemical behaviour of oxotitanium(IV) phthalocyanine (OTiPc) solutions associated with the preparation of OTiPC monolayers and multilayers

The chemical behaviour of oxotitanium(IV) phthalocyanine (OTiPc) in mixtures of dichloromethane and trihalogenoacetic acids was studied by means of spectroscopic measurements. In dichloromethane–trifluoroacetic acid mixtures, OTiPc was relatively unstable, undergoing gradual decomposition via the radical cation of OTiPc; phtalimide and 3-iminoisoindolin-1-one were isolated. In dichloromethane–trichloroacetic acid mixed solvent, on the other hand, a stable solution of OTiPc was obtained with no formation of the radical cation. A monolayer of OTiPc was formed upon spreading this solution onto the water surface and was deposited on substrates with a horizontal lifting method to form a multilayer film. Polarized visible and near-IR absorption spectra and X-ray diffraction of the film indicated a specific order of molecular orientation.

A charge-separated pair in thin crystals of oxotitanium(IV) phthalocyanine revealed by means of femtosecond time-resolved absorption

Abstract The formation and decay of a charge-separated pair in novel polymorphs of thin crystalline oxotitanium(IV) phthalocyanine (OTiPc)n (n>2) were studied by means of femto-second time resolved absorption spectroscopy. A rapid change of the time-resolved absorption spectrum in the range of 420–620 nm revealed that one-third of the intrinsic exciton of β-OTiPc ‖ exhibiting an absorption maximum around 550 nm was converted within 1 ps to a charge-separated pair exhibiting the absorption bands at 430, 510 and ca. 860 nm, which were assigned to a charge-separated pair. The assignment of cationic is π radical (OTiPc)n−1+ (n≥3) is based on the dimer formation of cationic radical in a solution of metallo-phthalocyanine. The anionic radical exhibits a similar absorption spectrum to that in a diluted solution. A time-resolved absorption spectrum of an amorphous crystal was also studied.

Characterization And Photoconductive Properties Of Highly Oriented Thin Films Of Oxotitanium Phthalocyanine Prepared By Vacuum Deposition Technique

Thin films of oxotitanium phthalocyanine were grown on optical flat PYREX glass substrates at 0.05 – 1.5 nm/s under 2×l0 -4 Pa. The films were analyzed by X-ray diffraction patterns (XRD) and polarized absorption spectra to reveal a preferred molecular orientation in the films evaporated at 0.05 nm/s, but amorphous nature of the films prepared at higher deposition rates. All the films were changed in the crystallinity to α-form Microcrystals upon exposure to vapor of methylene chloride or tetrahydrofuran. XRD analysis of the vapor-treated films at 0.05 nm/s showed only an intense peak at 2θ = 7.50°, demonstrating that the (010) face of the α-form crystal is highly oriented perpendicularly to the substrate surface. The Molecular orientation was again demonstrated by polarized absorption spectra. The photoconductive behavior of the films was found to depend on the deposition rates as well as on the vapor treatment.

Synthesis and second-harmonic generation properties of 2-(4-nitroanilino)-1,3,5-triazine derivatives

The synthesis and non-linear optical properties of a series of 2-(4-nitroanilino)-1,3,5-triazine compounds are described. The triazines show various activities in powder second-harmonic generation (SHG) depending on the structures and have absorption maxima at ⩽350 nm, shorter by 30–50 nm than those of the parent nitroanilines. 2-(4-Nitroanilino)-4,6-diphenyl-1,3,5-triazine affords different crystalline materials depending on the recrystallization solvent. A crystal formed by recrystallization from toluene reveals a high powder SHG activity comparable with that of 2-methyl-4-nitroaniline, while recrystallization from N,N-dimethylformamide gives an SHG-inactive crystal in which solvent molecules are incorporated in a 1:1 ratio by hydrogen bonding. The crystal structure of the latter was determined.