Direct observation of electric potential in organic EL devices by operando electron holography

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H02627
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 29020:Thin film/surface and interfacial physical properties-related
• Research Institution: Japan Fine Ceramics Center
• Principal Investigator: Yamamoto Kazuo 一般財団法人ファインセラミックスセンター, その他部局等, 主席研究員 (80466292)
• Co-Investigator(Kenkyū-buntansha): 吉本 則之 岩手大学, 理工学部, 教授 (80250637)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 有機EL / 電位分布 / 電子線ホログラフィー / 透過電子顕微鏡 / 機械学習

Outline of Final Research Achievements

The organic electro-luminescence (OEL) samples consisting of two layers, an alpha-NPD layer and an Alq3 layer, were fabricated using an organic film deposition system that we introduced in this project. A focused ion beam system was used to thin the sample with a thickness of 360 nm, and electron holography was used to directly observe the potential distribution in the two layers. The results showed that three regions with different electric fields were formed. The results of previous studies were also used as a reference to interpret the formation factors of the three electric field regions. We also developed a new electron holography technique using machine learning named 3D tensor decomposition method, which enables us to observe the electric potential distribution with an electron dose that is 1/60 lower than that of the conventional method. By using this technique, the effect of electron irradiation on the potential distribution in OELs was clarified.

Free Research Field

電子顕微鏡計測

Academic Significance and Societal Importance of the Research Achievements

本研究によって，有機EL内部の電位分布を直接可視化でき，これまで未解明であった有機半導体の学理構築に大きく寄与できると考えられる．これは有機ELにとどまらず，有機系太陽電池等，有機エレクトロニクス全般にも寄与するであろう．また，今回，電子線ホログラフィーと機械学習を用いた新たな観察技術を確立した．この技術により，より高速な物理現象や，電子線に脆弱な試料も観察可能となり，半導体分野の域を超えた幅広い分野（生物分野等）にも貢献できる．我々の生活に必須である電子デバイス（PCやスマートフォン等）は機能性材料を使用しているため，より高性能なデバイス開発により，より便利な社会構築にも寄与できる．