| AVS 56th International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Aspects of Thin Films Poster Session |
| Presenter: | K. Kato, Aoyama Gakuin University, Japan |
| Authors: | N. Oka, Aoyama Gakuin University, Japan K. Kato, Aoyama Gakuin University, Japan N. Ito, Panasonic Electric Works Co., Ltd., Japan T. Yagi, National Metrology Institute of Japan, AIST, Japan N. Taketoshi, National Metrology Institute of Japan, AIST, Japan T. Baba, National Metrology Institute of Japan, AIST, Japan Y. Sato, Aoyama Gakuin University, Japan Y. Shigesato, Aoyama Gakuin University, Japan |
| Correspondent: | Click to Email |
Organic light-emitting diodes (OLEDs) are promising for future lighting and display applications. It has been reported, however, that the electroluminescence properties are degraded by self-heating during operation [1,2]. In order to determine the heat propagation mechanism in OLEDs, it is important to measure the thermophysical properties precisely for the components of OLEDs, such as Tris-(8-hydroxyquinoline) aluminum (Alq3) and N,N'-Di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) films. Alq3 and α-NPD are used as the electron-transport/emitting materials and the hole-transport material, respectively. In this study, thermal diffusivity of both the films was characterized quantitatively by ‘rear heating / front detection (RF) type’ nanosecond thermoreflectance systems [3] (NanoTR, PicoTherm), which can directly observe the heat propagation through the film thickness. Alq3 and α-NPD films sandwiched between aluminum films (Al/Alq3/Al, Al/α-NPD/Al) were prepared on alkali-free glass substrates by means of vacuum evaporation . The nominal thicknesses of Al, Alq3 and α-NPD layer were respectively 100 nm, 50-200 nm and 100 nm. The thermal diffusivity of Alq3 films was found to be 1.4-1.6×10-7 m2/s, which is about 1.5 times higher than that of Alq3 powder [4]. Furthermore, the thermal diffusivity of α-NPD films is 1.2×10-7 m2/s. We also estimated the mean free path of phonons, lph, in terms of phonon propagation in Alq3 films using the thermal conductivity calculated from the thermal diffusivity, heat capacity per unit volume, and the average phonon velocity calculated from Young’s modulus and the density [5]. As a result, lph was approximately 0.49 nm, which is smaller than molecular size and intermolecular distance for Alq3, but almost twice the Al-N bond length [6,7].
<Acknowledgment>
This work was supported by New Energy and Industrial Technology Development Organization (NEDO) as a project of "Development of High-efficiency Lighting Based on the Organic Light-emitting Mechanism".
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