| AVS 56th International Symposium & Exhibition | |
| Thin Film | Friday Sessions |
| Session TF-FrM |
| Session: | Transparent Electronic Materials and Applications |
| Presenter: | N. Oka, Aoyama Gakuin University, Japan |
| Authors: | N. Oka, Aoyama Gakuin University, Japan H. Watanabe, Aoyama Gakuin University, Japan Y. Sato, Aoyama Gakuin University, Japan N. Ito, Panasonic Electric Works Co., Ltd., Japan H. Tsuji, Panasonic Electric Works Co., Ltd., Japan Y. Shigesato, Aoyama Gakuin University, Japan |
| Correspondent: | Click to Email |
Molybdenum trioxide (MoO3) films have been expected as a material that accelerates the hole-injection from the anode to the organic layer in organic light-emitting diodes (OLEDs) [1], where the hole-injection mechanisms into the organic layer have been discussed actively. It has been reported that the hole-injection performance of MoO3 films would be dependent on stoichiometry of the MoO3-x [2] and forming a charge-transfer complex between the MoO3 layer and the hole-transport layer (HTL) for OLEDs [3,4]. In this study, MoO3-x (x ≤ 1) films were deposited by radio frequency (rf) magnetron sputtering using a Mo metal target at a power of 200 W. Total gas pressure of the mixture of argon (Ar) and oxygen (O2) was maintained at 1.0 Pa. The O2 gas flow ratio (fO2) [O2/(Ar+O2)] during the sputtering process was varied 0-100%. The electronic state of the MoO3-x films near the surface was analyzed by X-ray photoelectron spectroscopy (XPS) and photoelectron spectrometry in air (PESA). The chemical shift of the XPS Mo3d peak revealed that the valence electron numbers of Mo were four or six for the film deposited at 10 % fO2, whereas it was approximately six for the films deposited at fO2 of higher than 15%. Furthermore, the PESA characteristics indicated that localized defect levels, caused by oxygen defects in MoO3-x, should be generated between the Fermi level and the valence band, the amount of which varied with fO2. These results suggest that the amount of oxygen in the films was controllable by appropriate adjustment of fO2. In order to evaluate the chemical reaction between each MoO3-x layer and HTL by Raman spectroscopy, bilayer films was fabricated by subsequent vacuum evaporation of N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) as HTL. The Raman spectra indicate that a charge transfer complex should be generated at an interface of the bilayers and the amount varied slightly with fO2, which could be expected to promote hole-injection and thereby enhance the device performance of OLEDs.
<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".
[1] T. Matsushima, G-H. Jin, H. Murata, J. Appl. Phys. 104, 054501 (2008).
[2] K. Sakanoue, Device Physics, Material Chemistry, and Device Application of Organic Light Emitting Diodes, CMC Publishing, 129 (2008) (in Japanese).
[3] W.-J. Shin, J.-Y. Lee, J. C. Kim, T.-H. Yoon, T.-S. Kim, O.-K. Song, Organic Electronics 9, 333 (2008).
[4] G. Xie, Y. Meng, F. Wu, C. Tao, D. Zhang, M. Liu, Q. Xue, W. Chen, Y. Zhao, Appl. Phys. Lett. 92, 093305 (2008).