The 214th MANA & 94th ICYS Joint Seminar
Dr. Tianyou Zhai, Dr. Xudong Yang and Prof. Ryo Yamada
| Date | July 15, Friday |
| Time | 15:30-17:15 |
| Place | Seminar room #431, MANA Bldg., NAMIKI Site, NIMS |
Download PDF file for seminar info.
15:30-16:00
One-Dimensional CdS Nanostructures: From Synthesis to Applications
As an important II-VI semiconductor, CdS (with a direct band gap of 2.5 eV) is one of the first semiconductors discovered and is probably ones of the most important electronic and optoelectronic materials with prominent applications in nonlinear optical devices, flat panel displays, light emitting diodes, lasers, logic gates, transistors, etc. It is also a decent active optical wavelength material and electrically driven lasing material, which may find wide applications in telecommunications, data storage, and near-field optical lithography. Compared with ZnO, CdS has the closet fundamental physical properties including crystal structures and lattice constants, and possesses superior properties including narrow bandgap, high transmittance in visible range, low work function, low surface recombination rate, and few oxygen vacancies. However, only little work focuses on CdS nanostructures compared to that of ZnO. Why? I think that there are three main reasons: First, difficulties in fabrication of high-quality structures; Second, poor properties, just a random characterization; Third, few practical applications. Here I will show my recent work to resolve these problems correspondingly, including rational fabrication, correlations between structures and properties, and photodetectors with high performances.
Speaker
Dr. Tianyou Zhai, ICYS-MANA Researcher, NIMS
Chair
Dr. Yoshio Bando, MANA COO, NIMS
16:00-16:30
Lost Charges from Short-Circuit Photocurrent in Dye-Sensitized Solar Cells with High Open-Circuit Voltage
Dye-sensitized solar cells (DSCs) are typical promising low cost solar cells as alternatives to traditional inorganic photovoltaic devices. Further enhancement of the open circuit voltage (Voc) and short circuit photocurrent (Jsc) is expected to achieve an energy conversion efficiency of DSCs to 15 % ~ 20% which is high enough for commercial power generation. However, efforts for high efficiency DSCs so far meet a dilemma that a significant improvement of the Voc is always accompanied with a decrease of Jsc. Here by using time resolved and integrated emission spectroscopy, we show that the lost charges from the photocurrent have been recombined by intra-molecular charge recombination (IMCR). In addition, IMCR has been significantly reinforced by the interactions between dye molecules and the additives used for Voc improvement. Moreover, IMCR is not sensitive to the quasi-Fermi-level or the electron density of the TiO2 layer which determines the Voc. These results strongly suggest that we may break through the dilemma by well controlling the IMCR and then high photocurrent in DSCs with high Voc is hopefully to be attained. Our findings indicate that IMCR is a crucial factor in the design of new dyes and additives for pursuing high efficiency DSCs.
Speaker
Dr. Xudong Yang, ICYS-Sengen Researcher, NIMS
Chair
Dr. Alexei Belik, MANA Independent Scientist NIMS
16:30-17:15
Charge and spin transport through single molecular junctions - experimental studies-
The mechanism of charge transport through single molecules is a key issue in molecular electronics. Charge transport through small and long molecules are expected to be dominated by tunneling and hopping mechanism, respectively. It is important to know the crossover length of the tunneling and hopping transport mechanism. In this study, we investigated scaling low and temperature dependence of the electrical resistance of Au/single oligothiophene molecule/Au junctions and found the crossover of the tunneling and hopping transport. In addition to the electrical resistance, magneto-resistance of Ni/benzene dithiol/Ni junction, which gives information on transport of spin polarized current through single molecular junctions, will be discussed.
Speaker
Prof. Ryo Yamada, Division of Materials Physics, Graduate School of Engineering Science, Osaka University
Chair
Dr. Kohei Uosaki, MANA PI, NIMS