Skip to main content Accessibility help

Energy Level Alignment at Bebq2/PEI/ITO Interfaces Studied by UV Photoemission Spectroscopy

  • Kohei Shimizu (a1), Hirohiko Fukagawa (a2), Katsuyuki Morii (a3), Hiroumi Kinjo (a1), Tomoya Sato (a1) and Hisao Ishii (a1) (a4) (a5)...


A polyethyleneimine (PEI) interlayer has been applied on indium tin oxide (ITO) to improve electron injection in organic devices including inverted organic light-emitting diodes (OLEDs). To understand the improvement effect by PEI insertion, the energy level alignment at bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2)/PEI/ITO interfaces was investigated by UV photoemission spectroscopy (UPS). The deposition of a PEI layer was found to reduce the absolute work function of ITO by 1.4 eV. The vacuum level shifts at Bebq2/ITO and Bebq2/PEI interfaces were also determined as 0.3 eV and 0.1 eV in the direction to reduce the electron injection barrier, respectively. Thus the work function reduction by PEI and downward vacuum level shift at the Bebq2/PEI interface can contribute to the improvement effect. Kelvin probe measurement revealed the weak orientation polarization in Bebq2 film with the bottom side positively polarized. This polarization polarity is also advantageous for electron injection in inverted devices.


Corresponding author


Hide All
1. Sessolo, M. and Bolink, H. J., Adv. Mater. 23, 1829 (2011).
2. Zhou, Y., Fuentes-Hernandez, C., Shim, J., Meyer, J., Giordano, A.J., Li, H., Winget, P., Papadopoulos, T., Cheun, H., Kim, J., Fenoll, M., Dindar, A., Haske, W., Najafabadi, E., Khan, T.M., Sojoudi, H., Barlow, S., Graham, S., Bredas, J.-L., Marder, S.R., Kahn, A. and Kippelen, B., Science 336, 327 (2012).
3. Fukagawa, H., Morii, K., Hasegawa, M., Arimoto, Y., Kamada, T., Shimizu, T. and Yamamoto, T., Appl. Phys. Express 7, 082104 (2014).
4. Ito, E., Washizu, Y., Hayashi, N., Ishii, H., Matsuie, N., Tsuboi, K., Ouchi, Y., Harima, Y., Yamashita, K. and Seki, K., J. Appl. Phys. 92, 7306 (2002).
5. Noguchi, Y., Miyazaki, Y., Tanaka, Y., Sato, N., Nakayama, Y., Schmidt, T.D., Brütting, W. and Ishii, H., J. Appl. Phys. 111, 114508 (2012).
6. Noguchi, Y., Lim, H., Isoshima, T., Ito, E., Hara, M., Won Chin, W., Wook Han, J., Kinjo, H., Ozawa, Y., Nakayama, Y. and Ishii, H., Appl. Phys. Lett. 102, 203306 (2013).
7. Kinjo, H., Lim, H., Sato, T., Noguchi, Y., Nakayama, Y. and Ishii, H., Appl. Phys. Express 9, 021601 (2016).
8. Machida, S., Ozawa, Y., Jun-ichi, T., Hiroshi, T., Nakayama, Y. and Ishii, H., Appl. Phys. Express 6, 25801 (2013).
9. Höfle, S., Schienle, A., and Bruns, M., Lemmer, U. and Colsmann, A., Adv. Mater. 26, 2750 (2014).
10. Fukagawa, H., Shimizu, T., Hanashima, H., Osada, Y., Suzuki, M. and Fujikake, H., Adv. Mater. 24, 5099 (2012).



Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed