Hostname: page-component-586b7cd67f-l7hp2 Total loading time: 0 Render date: 2024-11-25T18:02:55.887Z Has data issue: false hasContentIssue false
  • English
  • Français

Thin Interfacial Layers in Polymer-Based Electronics

Published online by Cambridge University Press:  21 March 2011

M. Fahlman ,
G. Greczynski ,
N. Johansson ,
S. Jönsson  and
W.R. Salaneck
M. Fahlman
Affiliation:
Department of Science and Technology, Linköping University, SE-601 74 Norrköping, Sweden
G. Greczynski
Affiliation:
Department of Physics, Linköping University, SE-581 83 Linköping, Sweden
N. Johansson
Affiliation:
Thin Film Electronics, S:t Larsgatan 23, SE-58224 Linköping, Sweden
S. Jönsson
Affiliation:
Department of Science and Technology, Linköping University, SE-601 74 Norrköping, Sweden
W.R. Salaneck
Affiliation:
Department of Physics, Linköping University, SE-581 83 Linköping, Sweden
Get access

Abstract

Electronic devices based on organic materials are presently being developed. In these devices, the cathode interface and the nature of the charge carrying species are often of crucial importance. In that context, the behavior of lithium atoms deposited on the surfaces of ultra-thin spin-coated films of poly(dioctyl-fluorene), PFO, and of condensed molecular solid films of tris(8-hydroxyquinoline) aluminum, Alq3, have been studied. The Li-atoms donate charges to the organic systems, leading to doping-induced electronic states in the otherwise forbidden energy gap. The changes in the electronic structure induced by charge transfer from the Li-atoms are different in the two materials studied, and depend upon the localization of the electronic states to which the electrons are transferred. In the case of the delocalized wave functions of the ∼-system of PFO, at low doping levels, the added charges lead to the formation of polaron states, while at higher doping concentrations, bipolaron states are formed. In the case of Alq3, however, up to a level of three added electrons per molecule, the added electrons reside in states localized on each of the three ligands. The role of thin (∼5 Å) interfacial layers of LiF or CsF between poly(9,9- dioctylfluorene) polymer film and an aluminum electrode was studied as well. LiF-deposition on poly(9,9-dioctyl-fluorene) did not cause doping of the polymer films, nor did the LiF dissociate at the interface. No significant shifts in the binding energy of the core levels nor any changes in the work function occurred. Al-deposition on LiF/PFO films did not cause dissociation of LiF, unlike the case for Alq3. We found that CsF does not dissociate when deposited on a polymer film. However, deposition of aluminum on CsF will cause dissociation with cesium n-doping the PFO film at the interface and fluorine likely reacting with aluminum to form AlF3. When deposited onto either of sputter-cleaned Al surface or Al with native oxide layer (AlxOy), CsF also was found to dissociate at the interface. CsF does not dissociate for Au/CsF/PFO and CsF/Au interfaces, which emphasizes the crucial role aluminum plays in the process. The observed decomposition of CsF occurring upon Al deposition and following Cs-doping of the surface region of PFO likely enhances injection of electrons into organic layer improving device performance. Since CsF dissociation is independent of the underlying material, the Al/CsF/emissive-material structure could be effective for almost all types of polymer/organic based electronic devices.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 660: Symposia JJ – Organic Electronic & Photonic Materials and Devices , 2000 , JJ6.6
Copyright
Copyright © Materials Research Society 2001

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Salaneck, W. R., Stafström, S., and Brédas, J. L., Conjugated polymer surfaces and interfaces: Electronic and chemical structure of interfaces for polymer light emitting devices (Cambridge University Press, Cambridge, 1996).Google Scholar
2. Salaneck, W. R., Friend, R. H., and Brédas, J. L., Electronic structure of conjugated polymers: Consequences of electron-lattice coupling, Phys. Rep. 319, 231 (1999).Google Scholar
3. Hung, L. S., Tang, C. W., and Mason, M. G., Appl. Phys. Lett. 70, 152 (1997).Google Scholar
4. Jabbour, G. E., Kawabe, Y., Shaheen, S. E., Wang, J. F., Morrell, M. M., Kippelen, B., and Peyghambarian, N., Appl. Phys. Lett. 71, 1762 (1997).Google Scholar
5. Shaheen, S. E., Jabbour, G. E., Morrell, M. M., Kawabe, Y., Kippelen, B., Peyghambarian, N., Nabor, M.-F., Schlaf, R., Mash, E. A., and Armstrong, N. R., J. Appl. Phys. 84, 2324 (1998).Google Scholar
6. Brown, T. M., Friend, R. H., Millard, I. S., lacey, D. J., Burroughes, J. H., and Cacialli, F., Appl. Phys. Lett. 77, 3096 (2000).Google Scholar
7. Kurosaka, Y., Tada, N., Ohmori, Y., and Yoshino, K., Jpn. J. Appl. Phys., 37, L872 (1998).Google Scholar
8. Li, F., Tang, H., Anderegg, J., and Shinar, J., Appl. Phys. Lett. 70, 1233 (1997).Google Scholar
9. Tang, H. and Shinar, J., Appl. Phys. Lett. 71, 2560 (1997).Google Scholar
10. Kim, Y.-E., Park, H., and Kim, J.-J., Appl. Phys. Lett. 69, 599 (1996).Google Scholar
11. Matsumura, M. and Jinde, Y., Appl. Phys. Lett. 73, 2872 (1998).Google Scholar
12. Siegbahn, K., Nordling, C., Fahlman, A., Nordberg, R., Hamrin, K., Hedman, J., Johansson, G., Bergmark, T., Karlsson, S.-E., Lindgren, I., and Lindberg, B., ESCA - Atomic, Molecules and Solid State Structure Studied by Means of Electron Spectroscopy (Uppsala, Sweden, 1967).Google Scholar
13. Sokolowski, E., Nordling, C., and Siegbahn, K., Phys. Rev. 110, 776 (1958).Google Scholar
14. Salaneck, W. R., Bergman, R., Sundgren, J.-E., Rockett, A., and Greene, J. E., Surf. Sci. 198, 461 (1988).Google Scholar
15. Curioni, A., Andreoni, W., Treusch, R., Himpsel, F. J., Haskal, E., Seidler, P., Heske, C., Kakar, S., Buuren, T. v., and Terminello, L. J., Appl. Phys. Lett. 72, 1575 (1998).Google Scholar
16. Lögdlund, M., Salaneck, W. R., Meyers, F., Bredas, J. L., Arbuckle, G. A., Friend, R. H., Holmes, A. B., and Froyer, G., Macromolecules 26, 3815 (1993).Google Scholar
17. Greczynski, G., Fahlman, M., Salaneck, W. R., Johansson, N., Santos, D. A. d., and Brédas, J. L., Thin Solid Films 363, 322 (2000).Google Scholar
18. Johansson, N., Osada, T., Stafström, S., Salaneck, W. R., Parente, V., Santos, D. A. dos, and Brédas, J. L., J. Chem. Phys. 111, 2157 (1999).Google Scholar
19. Greczynski, G., Fahlman, M., and Salaneck, W. R., J. Chem. Phys. 113, 2407 (2000).Google Scholar
20. Iucci, G., Xing, K., Lögdlund, M., Fahlman, M., and Salaneck, W. R., Chem. Phys. Lett. 244, 139 (1995).Google Scholar
21. Le, Q. T., Yan, L., Gao, Y., Mason, M. G., and Tang, C. W., J. Appl. Phys. In press.Google Scholar
22. Greczynski, G., Fahlman, M., and Salaneck, W. R., submitted (2000)Google Scholar
23. Mason, G., private communicationGoogle Scholar