Influence of the treatment of TCOs by UV-Ozone and
Oxygen Plasma on the performance of
electrophosphorescent devices
E. R. Santos1, G. Santos2, V. Deichmann3, E. C. Burini4,
S. H. Wang1, L. C. Akcelrud3, F. J. Fonseca2, A. M. de Andrade4
1
Escola Politécnica da Universidade de São Paulo, Departamento de Engenharia
Metalúrgica e de Materiais, SP, Brazil
2
Escola Politécnica da Universidade de São Paulo, Departamento de Engenharia de Sistemas
Eletrônicos, SP, Brazil
3
Universidade Federal do Paraná, Laboratório de Polímeros Paulo Scarpa, PR, Brazil
4
Instituto de Eletrotécnica e Energia da universidade de São Paulo, SP, Brazil
Since the appearance of the first OLED, its electroluminescence response as well as the role of
its individual components has been subject of many studies. As a matter of fact, the device’s
performance depends on its architecture, the thicknesses of the layers, besides the nature of the
material used as the emissive layer and the many interfaces. Rare earth complexes are good
candidates to give the OLEDs high luminance, since their singlet and triplet states act together
to produce light. Improvement of the interface between the transparent electrode (TCO) and
the polymer, according to the literature, has been achieved by surface treatments of the TCOs.
In this work, the surface of FTO (fluorinated tin oxide) 1 and ITO (indium tin oxide) films
deposited on glass were treated by UV-Ozone and Oxygen Plasma. These transparent
conductor oxide (TCO) films were used as anode in the OLEDs, which architecture
(TCO/PEDOT:PSS/PVK + Eu(20%)/Butyl-PBD/Al)2 was unchanged. Initially, the substrates
were cut into 1 inch x 1 inch, then the TCO surfaces were treated with UV-Ozone for 5
minutes3 or with Oxygen Plasma for 10 minutes. Immediately after the TCO treatment,
PEDOT:PSS and PVK + 20% Eu(DBM) 3bipy were deposited by spin-coating. Finally,
b-PBD and aluminum were thermally evaporated on the top. The devices were fully
characterized by electrical and optical measurements. The electrical sheet resistances of the
TCOs, their optical transmittances and thicknesses, and their surface morphology were
analyzed. The devices thus prepared presented very dissimilar electroluminescence behaviors;
however the UV-Ozone surface treatment lead to devices presenting a lower turn on voltage
and higher luminance than those prepared with the plasma oxygen treatment, and independent
of the kind of TCO. The I-V curves, electroluminescence spectra and luminance results were
obtained.
Keywords: Rare earth complex, UV-Ozone, oxygen plasma, transparent conductive oxide.
Thanks to FAPESP (proc.: 08/55862-9), CNPq, CAPES and University of São Paulo.
[1] L. S .Roman, R. Valaski, C. D. Canestraro, E. C. S. Magalhães, C. Persson, R. Ahuja, E.
F. da Silva Jr., I. Pepe, A. Ferreira da Silva, Appl. Surf. Sci. 252, 5361 (2006).
[2] G. Santos, PhD. Thesis, Escola Politécnica da Universidade de São Paulo (2008).
[3] E. R. Santos, PhD. Thesis, Escola Politécnica da Universidade de São Paulo (2009).
[email protected], Escola Politécnica da Universidade de São Paulo - Engenharia
Metalúrgica e de Materiais, Laboratório de Macromoléculas, Av. Prof. Mello Moraes, 2463,
Cidade Universitária, São Paulo, SP, CEP: 05508-970, Brazil, Phone: +55(11)3091-5480