Novel Conjugated Organic Dyes for Efficient Dye‐Sensitized Solar Cells

Novel conjugated organic dyes that have N,N‐dimethylaniline (DMA) moieties as the electron donor and a cyanoacetic acid (CAA) moiety as the electron acceptor were developed for use in dye‐sensitized nanocrystalline‐TiO₂ solar cells (DSSCs). We attained a maximum solar‐energy‐to‐electricity conversion efficiency (η) of 6.8 % under AM 1.5 irradiation (100 mW cm^–2) with a DSSC based on 2‐cyano‐7,7‐bis(4‐dimethylamino‐phenyl)hepta‐2,4,6‐trienoic acid (NKX‐2569): short‐circuit photocurrent density (J_sc) = 12.9 mA cm^–2, open‐circuit voltage (V_oc) = 0.71 V, and fill factor (ff) = 0.74. The high performance of the solar cells indicated that highly efficient electron injection from the excited dyes to the conduction band of TiO₂ occurred. The experimental and calculated Fourier‐transform infrared (FT‐IR) absorption spectra clearly showed that these dyes were adsorbed on the TiO₂ surface with the carboxylate coordination form. A molecular‐orbital calculation indicated that the electron distribution moved from the DMA moiety to the CAA moiety by photoexcitation of the dye.     

Dependence of the efficiency-bandwidth product on electrical volumeof small dielectric loaded antennas

The efficiency fractional efficiency bandwidth product (EB) that is expressed as a ratio of the radiation resistance to the absolute value of an input reactance of an antenna is used as a performance measure for small dielectric-loaded monopole antennas (DLMAs). The dependence of the efficiency bandwidth (EB) on the permittivity of the dielectric loading (i.e., the electrical volume) is experimentally investigated for the first time after we succeeded in measuring the small radiation resistance of the DLMAs precisely on the basis of the Wheeler cap method. As a result, it was found that the EBs of some DLMAs were enhanced over a bare monopole antenna and an EB characteristic curve has a maximum point. This result suggests the presence of the optimum electrical volume for the dielectric loading in order to obtain the best EB performance. A calculation by the finite-difference time-domain (FDTD) method was also conducted to confirm the presence of the maximum EB value under a certain condition. A general reason for the existence of the peak value is also explained using a mathematical deduction     

1.55-μm wavelength periodic traveling-wave photodetectorfabricated using unitraveling-carrier photodiode structures

We report the first periodic traveling-wave photodetector fabricated by using unitraveling-carrier photodiodes (UTC-PDs). The photodetector comprises three UTC-PDs with a 0.06-μm absorption layer that is periodically arranged along a coplanar waveguide transmission line. The photoresponse of the photodetector is three times larger than that of a single UTC-PD. A photodetector with terminal resistors at the input end achieves a 3-dB bandwidth of 115 GHz at 1.55 μm. This is almost the same value as that for a single UTC-PD. For one without terminal resistors, the 3-dB bandwidth degrades to 56 GHz as a result of the backward-propagating microwave being reflected at the input end. These results suggest that the photodetector is well designed with both velocity and impedance matchings     

Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission: trend in the deviation from the traditional way of estimating the interfacial electronic structures

The electronic structures of model interfaces of organic electroluminescent (EL) devices were investigated with UV photoemission spectroscopy (UPS). Interfaces of TTN (tetrathianaphthacene) and TCNQ (tetracyanoquinodimethane) were also studied as extreme cases for hole transport and electron transport material, respectively. For all organic/metal interfaces studied, the work function of metal electrode was changed by deposition of organic layer, i.e., the vacuum level was shifted at the interface, indicating the invalidity of the traditional energy level alignment model where a common vacuum level was assumed at organic/metal interface. At TCNQ/Au, DP-NTCI/Al, which are acceptor/metal interfaces, upward shift of the vacuum level of organic layer relative to that of metal was observed, suggesting the formation of interfacial dipole due to electron-transfer from metal to acceptor. At other organic/metal interfaces, TPD(N, N'-diphenyl-N, N'-(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine)/Au or ITO (indium tin oxide), ALq/sub 3/ (tris(8-hydroxyquinolino) aluminum)/Al, DP-NTCl(N, N'-diphenyl-1,4,5,8- naphthyltetracarboxylimide)/Al or Au, downward shift of the vacuum level was observed. Such downward shift has been also observed in our previous study for porphyrin/metal interfaces, and seems to be a trend for organic/metal interfaces at which no electron-transfer from metal to organic layer occurs. This trend suggests that the traditional model tends to underestimate (overestimate) the barrier height for hole (electron) injection. On the other hand, the vacuum level shift at ALq/sub 3//TPD interface was less than 0.1 eV, leading to an apparent applicability of the traditional model. However, it is not always the case for organic/organic interfaces: finite shift of 0.2 eV was observed at TTN/TCNQ interface due to electron-transfer from TTN to TCNQ. Possible origins of vacuum level shift at organic/metal interfaces were also discussed.     

Circularly polarised printed antenna fed by coplanar waveguide

A new structure of the circularly polarised printed antenna fed by coplanar waveguide (CPW) is proposed. FDTD analysis predicts the radiation of the circularly polarised wave from the antenna. The validity of this analysis is established by comparing with experimental results     

Analysis of higher information density pregroove model by boundary element method

Using the boundary element method, results of the push-pull ratio of differential output signals from an optical disc pregroove model by simulation are presented. The possibility of achieving higher information density by reducing the track pitch and the beam spot is demonstrated.<>     

Performance analysis of disk allocation method usingerror-correcting codes

The problem of distributing a Cartesian product file on multiple disks to maximize the parallelism for partial match queries is addressed. C. Faloutsos et al. (1989) have proposed an allocation method for Cartesian product files on multiple disks by using linear error-correcting codes. The performance of the allocation method is analyzed. Some conditions under which the allocation method is strictly optimal for queries with a given number of unspecified attributes are presented. A necessary and sufficient condition for a linear code to give a strictly optimal allocation method is discussed. Formulas for the average response time on queries with w unspecified attributes, denoted T_w, in terms of the weight distribution of the code or its dual code, and formulas for the average response time Ton all queries, are given. Several examples whose average response times T_w or T are close to theoretical lower bounds are presented     

Statistics of Rain Attenuation and other Environmental Effects Associated with the BSE Satellite Down-Link at 12 GHz in Japan

Propagation measurements were carried out at 12 GHz on the down-link of the Japan's Medium-scale Broadcasting Satellite for Experimental Purpose (BSE), launched in 1978. Analyses of the measurements have revealed the statistics of rain attenuation and duration of fade at 12 GHz in various parts and climates of Japan, as well as other environmental effects such as degradation of reception quality due to snowfall on receiving antennae, reduction in carrier-to-noise ratio by solar noise interference and diffraction attenuation by obstacles. This paper describes the results which are useful for planning and operation of satellite broadcasting systems.     

Evaluation of the Parallel Conductor Theory for Measuring Human Limb Blood Flow by Electrical Admittance Plethysmography

We devised a compensation technique that measures the admittance change of a limb submerged in an electrolyte solution in a cylinder. Using this technique, we evaluated the accuracy of admittance plethysmography and the validity of the parallel-conductor model on which the theory of blood flow measurement by electrical admittance (or impedance) plethysmography is based. From a theoretical point of view, if a limb is regarded as a parallel-conductor model, the admittance change due to blood pooling following venous occlusion should disappear when the resistivity of the solution is equal to that of the blood.     

7W operation of 644 nm wavelength laser diode arrays with index-guided structure

A 7 W operation of a red semiconductor array laser is achieved at a wavelength of 644 nm with high reliability for the first time. The uniform near-field pattern has been obtained by applying index-guided structure to the broad-stripe laser.