In an ideal model, a p-n junction is formed by two stacked slabs of semiconductors. Although the construction of actual devices is generally more complex, we show that such a simple method can in fact be applied to the formation of organic heterojunctions. Two films of the organic semiconductors poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) can be connected by a simple film-transfer method without disturbing their flat surfaces. Each film can further be modified with a surface-segregated monolayer to tune the strength and direction of the surface dipole moment. Using this method, we fabricated bilayer organic photovoltaic devices with interfacial dipole moments that were selected to align the energy levels at the heterojunction. The open-circuit voltages of the P3HT/PCBM devices could be tuned over a wide range between 0.3 and 0.95 V, indicating that, even if the same combination of bulk materials is used, the interfacial properties drastically alter the performance of organic photovoltaic devices.

Organic solar cells (OSCs) are promising low‐cost devices for generating electricity. In addition to fill factor, the short circuit current density (JSC) and the open circuit voltage (VOC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high JSC and VOC. However, the interfacial structures between the organic materials substantially affect the JSC and VOC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase VOC and decrease JSC, the trade‐off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in VOC without the reduction in JSC enhances the conversion efficiency of the OSCs by 30%.

This feature article focuses on the relationship between the interfacial structures constructed by molecular self-organization and the properties of organic photovoltaic devices. The use of self-assembled monolayers (SAMs) is reviewed for metal and metal oxide/organic interfaces, while surface-segregated monolayers (SSMs) are introduced as a new method for the modification of organic/organic interfaces. Research up to now has clearly demonstrated the effectiveness of the control of energy levels and other properties at the interfaces to enhance photovoltaic performance. The possibility of more precise control of the interfacial structures is also discussed.

Ultrasonic microspectroscopy technology, using the line-focus-beam and plane-wave ultrasonic material characterization system, is applied to characterization of silica glass. Eight types of commercial silica glasses fabricated by different production methods and conditions are used as specimens to measure their acoustic properties accurately, viz., acoustic velocity, density, elastic constant. The variations in those acoustic properties resulting from small amounts of impurities, such as hydroxyl ͑OH͒ and chlorine, incorporated during the production processes were quantitatively obtained. The longitudinal velocity, density, and elastic constant c 11 of silica glass with 860 ppm OH ions were less by 0.28%, 0.06%, and 0.62%, respectively, than those for OH-free silica glass, while the temperature coefficient of the longitudinal velocity was greater by 7.4%. In contrast, the leaky surface acoustic wave velocity, shear velocity and elastic constant c 44 of silica glass containing 1500 ppm residual chlorine were less by 0.23%, 0.30%, and 0.59%, respectively, than those of OH-free and chlorine-free silica glass, while the longitudinal velocity, elastic constant c 11 , and density increased slightly by 0.04%, 0.10%, and 0.02%, respectively. Further, it was found that the decrease in acoustic velocity due to OH or chlorine is mainly related to the decrease in the elastic constant, which also corresponds to the decrease in the viscosity of the SiO 2 material. These results demonstrate that the ultrasonic method is very useful and effective for analyzing and evaluating both the glass properties and the production processes.

The authors tested the effects on the tribological characteristics of refrigeration oils under refrigerant atmospheres using a block-on-ring tribometer. Based on the results of a sliding test using the tribometer, it was found that tricresyl phosphate (TCP) in both a polyol ester (POE) and alkylbenzene (AB) oil formed a lubricating film on the sliding surface under R410A atmosphere. Surface analyses revealed that a phosphate film had been formed on the sliding surface. With the POE oil in particular, the anti-wear effect of TCP greatly reduced the width of the wear track. It was also found that R32 interferes with the formation of phosphate films to a greater extent than does R410A. It is thought that the high polarity and the high reactivity of R32 with nascent metal surfaces prevent TCP from adsorbing to the Fe of the sliding surface. These results show that not only refrigeration oils but also refrigerants can have a major effect on the formation of the phosphate film in refrigeration systems. This knowledge could be helpful when designing new refrigeration systems.