Activity Report
Title of the Activity (活動名称)
Research Stay at Universität Augsburg – Spontaneous Orientation Polarization in Organic Thin Films
Affiliation / Year / Name (所属・学年・氏名)
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University
PhD Program, 2nd year
Zhangcheng Liao
Travel Period (渡航期間)
August 20, 2025 – October 15, 2025
Host Institution / Laboratory (渡航先・研究室名)
University of Augsburg, Germany
Prof. Wolfgang Brütting’s Group
Research Theme (研究課題)
Study of spontaneous orientation polarization (SOP) and temperature dependence in organic thin films for electron-transport applications.
Research Stay at University of Augsburg – Spontaneous Orientation Polarization in Organic Thin Films
From August 20 to October 15, 2025, I conducted a two-month research stay at the University of Augsburg in Germany under the supervision of Prof. Ken Albrecht (Kyushu University) and Prof. Wolfgang Brütting. My work was mainly carried out under the experimental guidance of Dr. Albin Cakaj in the Brütting Group. The purpose of this stay was to deepen my study of spontaneous orientation polarization (SOP) in amorphous organic thin films—an effect that can strongly influence the internal electric field and charge-injection efficiency of organic optoelectronic devices. The project aimed to understand how molecular structure, deposition rate, and temperature determine the formation of orientation-induced surface potentials, and how these microscopic polarization effects could be utilized for practical device applications. Besides the experiments, this stay also helped to build a closer connection between the Albrecht Group in Kyushu and the Brütting Group in Augsburg through daily technical discussions and comparison of measurement results.
Photo 1: The KP tip positioned close to the sample surface during measurement.
During the stay, a series of thin films were prepared by thermal evaporation and analyzed using multiple complementary techniques. Kelvin-probe (KP) measurements were performed on silicon substrates to evaluate the giant surface potential (GSP) as a function of film thickness and deposition temperature (Photo 1: The KP tip positioned close to the sample surface during measurement). Distinct temperature-dependent behavior was observed: at low deposition temperatures, certain amorphous films showed large positive potential gradients exceeding roughly 150 mV nm⁻¹, whereas at elevated substrate temperatures the orientation almost disappeared. These findings confirmed that the direction and magnitude of SOP can be tuned by the kinetic conditions during film formation. In parallel, ellipsometry was used to characterize the optical constants (n, k) and to explore how molecular orientation affects refractive-index anisotropy (Photo 2). The same setup, equipped with a heating stage for glass-transition (Tg) analysis, revealed that the materials remained amorphous up to about 130–150 °C, and that molecular mobility at higher temperatures led to partial relaxation of orientation polarization. In addition to the isomeric compounds used as reference systems, I also examined a dendrimer-type material possessing a higher Tg and excellent thermal durability. Its deposition required crucible temperatures around 400 °C, which provided useful insight into how molecular rigidity and branching influence film morphology and the stability of built-in polarization. Despite its bulky structure, the dendrimer film still showed a measurable, stable potential gradient (Photo 3–4), suggesting that high-Tg materials can sustain SOP if the molecular dipoles are appropriately arranged. To further verify the effect of orientation polarization on optical and electronic behavior, I fabricated bilayer structures and performed photoluminescence (PL) and angle-dependent PL (ADPL) measurements on films deposited on glass substrates (Photo 4). These complementary experiments helped me understand how SOP correlates with light-emission directionality and interface energetics. Throughout the experiments, careful attention was paid to film uniformity, reproducibility, and data consistency so that the results obtained in Augsburg could be directly compared with those measured previously in Fukuoka. By the end of the stay, I had established a unified measurement protocol that can be continuously used by both laboratories to promote further joint research on orientation-polarized organic semiconductors (Photo 1–4).
(Photo 2: Ellipsometry system with heating stage for Tg measurements.)
(Photo 3: ADPL measurement setup in glovebox)
This overseas stay became an important period of both scientific and personal growth. Scientifically, it broadened my understanding of how physical measurements link molecular design to macroscopic device performance. Through daily discussions with Dr. Albin Cakaj and regular feedback from Prof. Brütting, I learned how to interpret subtle changes in Kelvin-probe data, connect ellipsometric parameters to molecular orientation, and evaluate experimental reliability across different instruments. The well-equipped laboratory environment allowed me to explore various techniques—such as impedance analysis, optical modeling, and temperature-controlled deposition—that I had only partially used before in Japan. This experience will be highly valuable as I continue my doctoral research in the Albrecht Group. Outside the laboratory, living in Augsburg gave me practical experience in adapting to a new culture and language. The warm support of group members made everyday life much easier and more enjoyable. Communicating in English about both science and daily matters also helped me gain confidence in working within an international research environment. Looking ahead, I plan to extend the collaboration established during this stay toward device-level studies that directly link SOP strength with current–voltage behavior and emission stability. The knowledge and experience gained through this program have not only improved my experimental skills but also shaped my vision as a researcher—to contribute to the development of functional organic materials that combine molecular design with controlled orientation for next-generation energy-efficient devices.
(Photo 4: Sample storage and prepared thin films)
