Ichiro Hiromitsu

Ga-Doped ZnO Film as a Transparent Electrode for Phthalocyanine/Perylene Heterojunction Solar Cell

The photovoltaic properties of Zn–phthalocyanine (ZnPc)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) heterojunction solar cells using Ga-doped ZnO (GZO) film as a transparent electrode are studied. When GZO is the electrode in contact with the donor layer, i.e., ZnPc, the energy conversion efficiency η is only 1/4 of that for the cell using indium–tin-oxide (ITO) as the electrode. When GZO is the electrode in contact with the acceptor layer, i.e., PTCBI, on the other hand, the cell has a three times larger η than the cell using ITO. These results are explained by the work function of GZO being lower than that of ITO. When GZO, or ITO, is used as an electrode for PTCBI, an interesting aging effect is observed. For example, by keeping the GZO-based cell in open air for 6 days in the dark, the energy conversion efficiency and the short-circuit current are increased by factors of 1.67 and 1.36, respectively.

Electric field in phthalocyanine/perylene heterojunction solar cells studied by electroabsorption and photocurrent measurements

The electric-field distribution in Au/Zn-phthalocyanine(ZnPc)/3,4,9,10-perylene-tetracarboxylbis-benzimidazole(PTCBI)/In/Al heterojunction solar cells is studied by electroabsorption and photocurrent measurements. In the PTCBI surface region near the PTCBI/In interface, a large anomalous electric field exists which is nearly bias independent and does not contribute to the photocurrent generation. This anomalous electric field exists only for the PTCBI-film thickness ⩾35 nm. The electric fields in the bulk of the PTCBI and ZnPc layers are responsible for the photocurrent generation. The bulk electric field in the PTCBI layer changes its sign at a forward bias, Vbias, of 0.3 V, while that in the ZnPc layer disappears for Vbias⩾0.5 V. The latter may indicate that holes are hardly trapped in the ZnPc layer.

A pressure dependent antiferromagnetism of AlPcf•(TCNE)x film

Magnetic properties of fluoro-aluminum phthalocyanine (AlPcF) film doped with tetracyanoethylene (TCNE) are studied by ESR. A strong pressure dependence is observed: At 760 Torr an antiferromagnetic transition takes place at 175±3 K, while, in vacuum, no magnetic transition is observed. DC conductivity does not have any pressure dependence. An X-ray diffraction study indicates that a pressure dependence of interlayer distance inside the film is a structural origin of the pressure dependence of the magnetism. A resonance mechanism of a charge transfer between AlPcF cation radical (AlPcF + ·) and TCNE anion radical (TCNE - ·) is proposed in order to explain an interchain magnetic coupling.

Synthesis and magnetic properties of polymeric complexes containing ruthenium(II)-ruthenium(III) tetracarboxylato units linked by cyanato, thiocyanato, and selenocyanato ligands

Polymeric complexes of ruthenium(II)-ruthenium(III) tetracarboxylato units linked by cyanato, thiocyanato, and selenocyanato ligands [Ru2{O2C(CH2)mCH3}4(L)]n (m = 0, 4–7; L = OCN−, SCN−, and SeCN−) were prepared and characterized based on the elemental analyses, IR, and diffuse reflectance spectra. Magnetic susceptibilities were measured at the temperature range of 4.5 K to 300 K, where the interdimer antiferromagnetic interactions were revealed. The strongest interaction was exhibited in case of m = 7 and L = OCN−. 1H-NMR spectra of [Ru{O2C(CH2)7CH3}4(SCN)]n in CD2Cl2 showed broad signals which can be ascribed to polymeric species, as the addition of tetrabutylammonium thiocyanate caused sharper signals due to the formation of [Ru2{O2C(CH2)7CH3}4(SCN)2]− adduct as the main species in the solution.

A non-ideal bias dependence of the inner electric field in Au/Zn-phthalocyanine/Al photovoltaic cells studied by electroabsorption and photocurrent measurements

Electroabsorption (EA) and photocurrent measurements are done for Au/Zn-phthalocyanine (ZnPc)/Al sandwich cells in order to study the bias dependence of the inner electric field in the ZnPc layer. The bias dependence of the EA signal intensity and photocurrent is not explained by the conventional models for the inner electric field in the following features. 1) The EA intensity and the photocurrent disappear at different bias voltages, i.e. 1.24 and 0.47 V, respectively. 2) The EA intensity does not have a simple linear dependence on the bias voltage. 3) The photocurrent is kept zero with the bias voltage higher than 0.47 V. The results are consistently explained by a model in which an interfacial layer and surface states exist at the ZnPc/Al junction.

Synthesis and Magnetic Property of Adducts of Ruthenium(II,III) Pivalate with 9,10-Anthraquinone

Abstract Reaction of tetrakis(pivalato)diruthenium(II,III) cation dimer and 9,10-anthraquinone (aq) gave two kinds of adducts, [{Ru2(piv)4(H2O)}2(aq)]-(BF4)2 (1) (pivH = pivalic acid) and [Ru2(piv)4(aq)] n (2), depending on the condition. Very weak antiferromagnetic interaction was observed for 1. The X-ray crystal structure of 2 shows an one-dimensional chain structure.

Occurrence of Antiferromagnetic Transition in Iodine Doped AlPcF Film

Magnetism of iodine doped fluoro-aluminum phthalocyanine (AlPcF) film is studied by electron spin resonance (ESR) in two stable doping states: In State I, a doped AlPcF film is always in contact with saturated I 2 gas (AlPcF·I 4.0 ); In State II, a doped film is in no contact with I 2 gas (AlPcF·I 0.10 ). An antiferromagnetic transition is observed in both states. In State I in vacuum, the transition temperature depends on samples and the highest transition temperature observed is 160 K. In State II, it does not depend on samples and is 150 K in vacuum and 220 K at 1 atm. The occurrence of the magnetic transition indicates an existence of three dimensional magnetic coupling, i.e. interchain and intrachain couplings. An information about back charge transfer probability from I 3 - to AlPcF· + in State II is obtained from a degree of g anisotropy. With a help of this information, possible mechanisms of the interchain coupling are discussed.

Correlation between Inner Electric Field and Photocurrent of Zn-Phthalocyanine Schottky-Barrier Cells

An electroabsorption (EA) study is carried out at an electric-field modulation frequency ωm/(2π) of 1 Hz for two types of typical organic Schottky-barrier cell, namely, Au/Zn-phthalocyanine (ZnPc)/Al and Au/ZnPc/In/Al, in order to elucidate the role of the inner electric field in photocurrent (Iphoto) generation. From the bias dependence of the 1F- and 2F-EA intensities measured at the frequencies of ωm and 2ωm, respectively, it is shown that the inner electric field E0 as well as the modulation electric field Em is quenched in the ZnPc layer with a forward bias larger than ~1 V. For Au/ZnPc/Al, a good correlation is observed between E0 and Iphoto, which indicates that Iphoto is generated by E0. For Au/ZnPc/In/Al, on the other hand, no correlation is observed between E0 and Iphoto. An interpretation of the latter is that Iphoto is caused by an increase in charge-injection probability at the ZnPc/In interface as a result of the trapping of photogenerated charges in the interface region. For both systems, the depletion layer is detected by capacitance-voltage measurement at 0.2 Hz.

Dinuclear Phenoxo-Bridged Nickel(II) Complexes of Macrocyclic Ligands with Cyano Groups Laterally Introduced on a Conjugated System within the Ligands

Abstract Diphenoxo-bridged dinuclear nickel(II) complexes of macrocyclic ligands having two cyano groups laterally introduced on a π-conjugated system within the ligands have been prepared and characterized. The reaction solvent DMF is coordinated to the nickel(II) ions to cause them high spin state. The antiferromagnetic interaction (J = ca. -10 cm−1) was observed between the nickel(II) ions.

Photovoltaic effect and electrically detected electron spin resonance of a H2-phthalocyanine/C60 heterojunction

The Au/H2-phthalocyanine(H2Pc)/C60/Au heterojunction shows a photovoltaic effect with the conversion efficiency of 0.02%. An electrically detected electron spin resonance (EDESR) study is done for this system. The observed EDESR signal represents a decrease of the photocurrent due to the spin-dependent recombination of the localized electron-hole pair which is created by the photoinduced charge transfer between the H2Pc and the C60. The microwave-power-saturation behavior of the EDESR signal is not explained by the formula generally used.