7th International Conference of Sabaragamuwa University of Sri Lanka (ICSUSL) 2019
http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/388
2024-03-28T09:35:26ZICSUSL - 2019 “Frontier Technologies for a Sustainable Future”
http://repo.lib.sab.ac.lk:8080/xmlui/handle/123456789/776
ICSUSL - 2019 “Frontier Technologies for a Sustainable Future”
2019-11-14T00:00:00ZTOWARDS UNDERSTANDING AND CONTROLLING SPONTANEOUS ORIENTATION POLARIZATION IN ORGANIC SEMICONDUCTING FILMS
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.
2019-11-14T00:00:00ZRECENT DEVELOPMENTS AND RESEARCHES BY USING SCANNING TRANSMISSION X-RAY MICROSCOPY IN UVSOR SYNCHROTRON
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.
2019-11-14T00:00:00ZPHOTOVOLTAIC PROPERTIES OF SEMI-TRANSPARENT ORGANIC SOLAR CELL
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