Is there any dependence on the exposure time? If yes, how can it be tuned? UV-ozone treatment makes the ITO surface smooth and avoids any shorts between the various layers while fabricating organic/polymer based optoelectronic devices. It is said that the ITO work function is increased and the conductivity is reduced.
The influence of the ultraviolet -ozone treatment of indium tin oxide (ITO) surface was explored in a few studies and they agreed on an increased ITO work function after exposure which depends on the exposure time. Also, my observation is that after exposure to UV-Ozone it becomes very hydrophylic. Of course the time should have an influence as the amount of organics (carbon) removed will depend on the time.
In one of the articles it is explained by XPS: "X-ray photoelectron spectroscopy results showed that the relative concentration of carbon atoms decreased, but oxygen concentration increased relatively with UV–ozone treatment. This led to the increase in the ITO work function via the reduction of operation voltage."
[1]S. Y. Kim, J.-L. Lee, K.-B. Kim, and Y.-H. Tak, “Effect of ultraviolet-ozone treatment of indium tin oxide on electrical properties of organic light emitting diodes,” Journal of Applied Physics, vol. 95, no. 5, pp. 2560 –2563, Mar. 2004.
In another one it is explained with ITO surface contamination: Cleaning the surface would change ITO work function (values ranging between 4.1 and 5.2 eV). In this article they especially reported on treatment duration (min) and its influence on work function and atomic concentration. You can read this article and would be useful I believe.
[2] P. Destruel, H. Bock, I. Séguy, P. Jolinat, M. Oukachmih, and E. Bedel-Pereira, “Influence of indium tin oxide treatment using UV–ozone and argon plasma on the photovoltaic parameters of devices based on organic discotic materials,” Polymer International, vol. 55, no. 6, pp. 601–607, 2006.
"UV–ozone treatment on ITO surface would remove the surface carbon atoms and increase the surface oxygen concentration, thereby raise the work function of the ITO." [3] T. Hu, F. Zhang, Z. Xu, S. Zhao, X. Yue, and G. Yuan, “Effect of UV–ozone treatment on ITO and post-annealing on the performance of organic solar cells,” Synthetic Metals, vol. 159, no. 7–8, pp. 754–756, Apr. 2009.
This is deviation from stoichiometry.
You generates vcancies in indium sublattice and this forms additionakl levels in the gap. Thus, you get doped semiconductor with modified work function.
Usually UV/ozone treatment increases the work function due to oxidation of the surface and this shifts depends on the ozone concentration and the exposure time. Usually after enough long exposure (~30 min?) it is about 5 eV. More important is already mentioned cleaning of the surface. UV/ozone treatment destroys organic residues on the surface. Further, the surface oxidation changes the wetting properties and the surfase is more hydrophilic (i.e. the contact angle for water decreases). This will, of course, influence spin-coated polymer-based films which are you talking about. The reduction of conductivity is almost negligible since the only surface is influenced.
The influence of the ultraviolet -ozone treatment of indium tin oxide (ITO) surface was explored in a few studies and they agreed on an increased ITO work function after exposure which depends on the exposure time. Also, my observation is that after exposure to UV-Ozone it becomes very hydrophylic. Of course the time should have an influence as the amount of organics (carbon) removed will depend on the time.
In one of the articles it is explained by XPS: "X-ray photoelectron spectroscopy results showed that the relative concentration of carbon atoms decreased, but oxygen concentration increased relatively with UV–ozone treatment. This led to the increase in the ITO work function via the reduction of operation voltage."
[1]S. Y. Kim, J.-L. Lee, K.-B. Kim, and Y.-H. Tak, “Effect of ultraviolet-ozone treatment of indium tin oxide on electrical properties of organic light emitting diodes,” Journal of Applied Physics, vol. 95, no. 5, pp. 2560 –2563, Mar. 2004.
In another one it is explained with ITO surface contamination: Cleaning the surface would change ITO work function (values ranging between 4.1 and 5.2 eV). In this article they especially reported on treatment duration (min) and its influence on work function and atomic concentration. You can read this article and would be useful I believe.
[2] P. Destruel, H. Bock, I. Séguy, P. Jolinat, M. Oukachmih, and E. Bedel-Pereira, “Influence of indium tin oxide treatment using UV–ozone and argon plasma on the photovoltaic parameters of devices based on organic discotic materials,” Polymer International, vol. 55, no. 6, pp. 601–607, 2006.
"UV–ozone treatment on ITO surface would remove the surface carbon atoms and increase the surface oxygen concentration, thereby raise the work function of the ITO." [3] T. Hu, F. Zhang, Z. Xu, S. Zhao, X. Yue, and G. Yuan, “Effect of UV–ozone treatment on ITO and post-annealing on the performance of organic solar cells,” Synthetic Metals, vol. 159, no. 7–8, pp. 754–756, Apr. 2009.
Thank you very much Dilek for the detailed answer to my question.
surprisingly 6.1ev! Interplay of cleaning and de-doping in oxygen plasma treated high work function indium tin oxide (ITO)
by: Irfan Irfan, Sachiko Graber, Franky So, Yongli Gao
Organic Electronics, Vol. 13, No. 10. (October 2012), pp. 2028-2034
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