http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/388 2026-04-17T00:39:35Z http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/776 ICSUSL - 2019 “Frontier Technologies for a Sustainable Future” 2019-11-14T00:00:00Z http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/775 TOWARDS UNDERSTANDING AND CONTROLLING SPONTANEOUS ORIENTATION POLARIZATION IN ORGANIC SEMICONDUCTING FILMS Noguchi, Y; Osada, K; Ishii, H Spontaneous orientation polarization (SOP) is inherent in evaporated films of many organic semiconducting molecules with a permanent dipole moment (PDM). A significant electric field is formed in the film due to SOP. Consequently, the properties of organic light-emitting diodes (OLEDs) incorporating such films are influenced. However, the formation mechanism of SOP has been insufficiently understood. First of all, we examined more than 15 OLED materials for SOP towards understanding and controlling SOP. The results indicate that SOP is very common in evaporated films of OLED materials. Furthermore, the results imply that the strong electrostatic interaction between PDMs acts as a negative factor of the SOP formation. Next, SOP of co-evaporated films was also studied. In the co-evaporated films of TPBi and CBP, where TPBi is polar while CBP is non-polar, we found that the orientation degree of PDM increases with diluting PDM density. This result is consistent in terms of the electrostatic interaction. Since the concentration of PDM is diluted by the nonpolar molecule, the electrostatic interaction energy is reduced. As suppressing negative factor, the orientation degree of PDM is enhanced. Finally, we examined the surface potential characteristics of TPBi films deposited on a gold substrate with/without a self-assembled monolayer (SAM) of 1-dodecanethiol. The surface potential of the SAM treated sample was lower than that of the untreated one. The result can also be explained by considering electrostatic interactions. By reducing surface free energy, van der Waals interaction on the film surface is suppressed and PDM interaction becomes relatively dominant, consequently SOP is suppressed. In summary, the SOP formation likely results from a balance between positive and negative factors, where the positive factor is the van der Waals interaction between the molecule and film surface, and the negative factor is the PDM interaction between molecules on the film surface. 2019-11-14T00:00:00Z http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/774 RECENT DEVELOPMENTS AND RESEARCHES BY USING SCANNING TRANSMISSION X-RAY MICROSCOPY IN UVSOR SYNCHROTRON Ohigashi, T; Yuzawa, H A scanning transmission X-ray microscope (STXM) is a synchrotron radiation-based analytical tool to acquire 2-dimensional X-ray absorption spectra of a sample. Generally, STXM uses a Fresnel zone plate as a focusing optics for X-rays and spatial resolution higher than 30 nm became available in these years. By using STXM in soft X-ray region, many absorption edges of light elements and transition metals exist and detailed analysis of their near edge X-ray absorption fine structures (NEXAFS) brings us chemical state of the specific elements. One of remarkable advantages of STXM is flexibility of environment around a sample, since the Xray has high transmittance. This advantage enables STXM to measure the sample in water, in humidity or in atmospheric pressure by designing special sample cells. Hence, at a STXM beamline, BL4U , in UVSOR synchrotron (Okazaki, Japan), we have been developing special measurement techniques such as in-situ electrochemistry, in-situ humidity control techniques, 3-dimensional spectroscopy by using computer tomography and the other techniques which are quite difficult to perform for the other microscopic tools. In this presentation, developments, recent researches, and a collaborative project among several facilities, linkage analytical techniques in Hayabusa2 project, will be shown. 2019-11-14T00:00:00Z http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/772 PHOTOVOLTAIC PROPERTIES OF SEMI-TRANSPARENT ORGANIC SOLAR CELL Tanaka, S Organic solar cell (OSC) is one of the emerging solar cells for the next generation. OSCs have attracted much interest since it has unique functions such as flexibility, lightweight, availability of low-cost fabrication processes, and semi-transparency of the photoactive layer, etc. Many kinds of studies have been conducted to fulfill the requirements for practical use. Especially the understanding of photovoltaic mechanisms in the OSC is critically important to enhance its efficiency. In this presentation, we will discuss the working mechanism of OSC thorough our resent study of semi-transparent OSCs. As a semi-transparent OSC, we have fabricated OSCs with two transparent electrodes, which are a carbon nanotube (CNT) sheet as the top transparent electrode and an indium tin oxide (ITO) as the bottom one. The illumination direction dependence on the photovoltaic properties of semi-transparent OSC was studied. It was found that the power conversion efficiency (PCE) under the CNT side illumination showed a lower value than that under the ITO side illumination. To understand the origin of the asymmetricity of photovoltaics, we fabricated semi-transparent OSCs with different thickness of the active layer and explored the illumination direction dependence of the photovoltaic properties. It was found that the discrepancy of the PCE between the ITO side and the CNT side was increased with the increase of thickness. We consider three possible origins of asymmetry: the difference in the transparency of electrodes, the polymer segregation, and the difference in the extraction efficiency of carriers. The CNT electrode had lower transparency than the ITO electrode. In addition, the polymer segregation at the CNT electrode side reduced the light intensity. These effects lower a PCE of constant value under CNT side illumination but do not explain the thickness dependence of asymmetry. The main factor for the asymmetry is the extraction efficiency. From the comparison of experimental photocurrent and simulated carrier densities, we estimated that the hole extraction efficiency is higher than the electron one. The present results infer that the detailed analysis of photovoltaic properties of semi-transparent solar cells provides fruitful insight into the photovoltaic mechanism of OSCs. 2019-11-14T00:00:00Z