Origin of the open-circuit voltage of organic thin-film solar cells based on conjugated polymers

Recently, efficiency of organic solar cells (OSCs) with conjugated polymers and fullerene derivatives has been increased, in most cases by improving their short-circuit current density. Regarding the other photovoltaic parameters, the open-circuit voltage (V_OC) remains controversial. In this study, we investigated the relation between the V_OC and the energy difference (ΔE) between the highest occupied molecular orbital of the donor material and the lowest unoccupied molecular orbital of the acceptor. The simple linear relation between V_OC and ΔE was not observed in the polymer-based OSCs. There must be some factor that decreased the V_OC of the cells.     

Novel copper immersion coating on magnesium alloy AZ91D in an alkaline bath

Copper immersion coating of magnesium alloys has, to date, been conducted only in acidic baths. This article describes a novel alkaline bath for copper immersion coating on AZ91D magnesium alloy. Prior to the coating process, a chemical etching process of the magnesium substrate was optimized using orthogonal experimental methodology. The copper immersion coating was then investigated with regard to the effect of pH and fluoride content in the deposition bath. It was revealed during the coating process that an increase of pH and fluoride content led to a surface film formation on the magnesium substrate. The surface film formation occurred simultaneously with copper reduction, rendering a controlled magnesium dissolution, thereby a controlled copper deposition. With optimized conditions of chemical etching and immersion coating processes, uniform copper deposits were achieved.     

Photocurable biodegradable polyesters from poly(L‐lactide) diols

α,ω‐Dihydoxy‐terminated poly(L ‐lactide)s (PLLA diols) with various molecular weights (1000, 2000 and 3000 g mol^?1) were prepared by the ring‐opening polymerization of L ‐lactide using 1,6‐hexanediol as an initiator. These were subsequently chain‐extended with the diacyl chloride of 4,4′‐(adipoyldioxy)dicinnamic acid (CAC) to obtain high‐molecular‐weight photocurable polyesters (CAC/PLLAs). The resulting polyesters were characterized by gel permeation chromatography, Fourier‐transform infrared, ultraviolet–visible and proton nuclear magnetic resonance spectroscopies, differential scanning calorimetry and thermogravimetry. These photoreactive polyesters were irradiated with a high‐pressure mercury lamp (λ > 280 nm) for 30–180 min to produce the crosslinked polyesters. The gel fraction yield increased with photocuring time, and exceeded 80 % after 180 min. The photocuring process disturbed the crystallization of the CAC/PLLA films, while it enhanced their thermal stabilities. With increasing photocuring time, both the tensile strength and modulus increased markedly. The best mechanical properties (tensile strength = 41 MPa; tensile modulus = 1550 MPa) were obtained for a CAC/PLLA‐3000 film photocured for 180 min. The tensile modulus of this photocured film was larger than that of pure PLLA. The hydrolytic degradation rates of the CAC/PLLA films in a phosphate buffer solution (pH, 7.2) of proteinaze‐k at 37 °C were much slower than those of pure PLLA films. Copyright © 2004 Society of Chemical Industry     

A built-in technique for probing power supply and ground noise distribution within large-scale digital integrated circuits

Design of noise detector circuits as compact as standard logic cells is proposed. High-density large-scale digital integrated circuits that embed such built-in noise detectors enable in-depth characterization of dynamic power supply and ground noises. Dependence of power supply and ground voltage drops on the location of active cell rows within 1.8-V standard cell-based digital circuits are consistently measured by 1.8- and 2.5-V built-in detectors fabricated in a 0.18-/spl mu/m CMOS triple-well technology. Measurements also show that ground noise distribution is distinctively more localized than power supply counterparts due to the presence of a substrate.     

Doping effects for organic photovoltaic cells based on small-molecular-weight semiconductors

We have studied highly efficient organic photovoltaic (OPV) cells based on small-molecular-weight semiconductors: zinc phthalocyanine (ZnPc) and C60. To improve the efficiency furthermore, open-circuit voltage (V_oc) has to be increased. We reported that 5,6,11,12-tetraphenylnaphthacene (rubrene) produces the highest V_oc of 0.91 V by p–n heterojunction OPV cells with C60. In this paper, we report rubrene doping effects for OPV cells based on ZnPc to obtain higher V_oc.     

Three‐dimensional analysis of light transmittance characteristics in many index ellipsoids connected in series

The three‐dimensional optical technique has been applied to analysis of the experimental results related to magnetic wave scattering phenomena. Recently, we have developed an ideal equation for analyzing the three‐dimensional transmittance character of light scattered due to many index ellipsoids. The index ellipsoids are arranged directly along the light axis in series. In this case, the index ellipsoid size and the gap distance between each index ellipsoid and neighbor one are considered as a calculation condition. By using an analysis equation devised by us, we have sought to determine the condition under which the light can be passed through many transparent mediums with high efficiency. From the numerical calculations, the condition for maximum transmittance of light 100% is obtained when a spherical and elliptic index ellipsoids are alternately arranged with respect to each other. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 12–18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20311     

Off-line error prediction, diagnosis and recovery using virtual assembly systems

Automated assembly systems often stop their operation due to the unexpected failures occurred during their assembly process. Since these large-scale systems are composed of many parameters, it is difficult to anticipate all possible types of errors with their likelihood of occurrence. Several systems were developed in the literature, focussing on on-line diagnosing and recovery of the assembly process in an intelligent manner based on the predicted error scenarios. However, these systems do not cover all of the possible errors and they are deficient in dealing with the unexpected error situations. The proposed approach uses Monte Carlo simulation of the assembly process with the 3-D model of the assembly line to predict the possible errors in an off-line manner. After that, these predicted errors are diagnosed and recovered using Bayesian reasoning and genetic algorithms. Several case studies are performed on single-station and multi-station assembly systems and the results are discussed. It is expected that with this new approach, errors can be diagnosed and recovered accurately and costly downtimes of robotic assembly systems will be reduced.     

A minimal lattice realization for multivariable systems

An algorithm for constructing a minimal lattice realization of a multivariable stable linear discrete-time system is proposed. The algorithm consists of four steps: (i) realize the objective system in an input normal Hessenberg form, (ii) construct an LBR system associated with the objective system, (iii) construct a lattice realization of the LBR system from its input normal Hessenberg realization, (iv) transform the lattice realization of the LBR system into one of the objective system.     

Side reactions of phenylisocyanate in N,N-dimethylacetamide

Side reactions of isocyanate groups in N,N-dimethylacetamide (DMAC) were studied. Although 4,4′-diphenylmethane diisocyanate (MDI) in DMAC was stable and no changes occurred at 3°C, the isocyanate content decreased and a gel was finally formed at 40°C. Using phenyl isocyanate (PI) as a model compound of MDI, the identification of PI side-reaction products in DMAC were studied. From these experiments, the following five products were identified; (1) 1,3-diphenylurea (DPU), (2) 1,3-diphenyl-5-phenylcarbamyl-6-dimethylaminouracil (PUR), (3) 1,3,5-triphenylbiuret (TPB), (4) triphenyl-s-triazine-2,4,6-trione (TTT), and (5) 1,1-dimethyl-3-phenylurea (DMPU). Among these identified products, the novel side reaction product PUR, which was formed between PI and DMAC as solvent, was found along with TPB and TTT, which were already known to cause three-dimensional network formation.