Sol gel deposited Sb doped SnO2 as transparent anode for OLED:: process, patterning and hole injection characteristics

This paper reports on the potentialities of sol-gel deposited Sb doped SnO2 (TO) as a new transparent conducting oxide (TCO) for anode in organic light emitting diodes (OLED). Multilayered films with transparency over 85% and resistivity lower than 5 10(-3) Omega-cm were obtained. Structural observations by Transmission Electron Microscopy (TEM) show that the films are nanocrystallized. Smaller and more uniform grains are obtained upon rapid thermal annealing. Atomic Force Microscopy (AIM) imaging shows the surface roughness does not exceed 20 Angstrom. TO films are very stable and cannot be chemically etched. Anode patterning by reactive ion etching (RIE) in a Methane-Hydrogen plasma has been experienced and is described. Typical etching around 250 Angstrom/min were obtained. TO/PEDOT/PVK/Al hole only diodes were realized to assess sot gel TO films as hole injection electrodes. Devices with threshold voltages of 6 volts were obtained. A comparison with ITO deposited by low temperature cathodic sputtering is given.