Thin film hexagonal gold grids as transparent conducting electrodes in organic light emitting diodes

Abstract

Indium Tin Oxide (ITO) coated glass is currently the preferred transparent conducting electrode (TCE) for organic light emitting diodes (OLEDs). However, ITO has its drawbacks, not least the scarcity of Indium, high processing temperatures, and inflexibility. A number of technologies have been put forward as replacements for ITO. In this paper, an OLED based on a gold grid TCE is demonstrated, the light emission through the grid is examined, and luminance and current measurements are reported. The gold grid has a sheet resistance of 15 Ω□-1 and a light transmission of 63 % at 550 nm, comparable to ITO, but with advantages in terms of processing conditions and cost. The gold grid OLED has a lower turn-on voltage (7.7 V versus 9.8 V) and achieves a luminance of 100 cdm-2 at a lower voltage (10.9 V versus 12.4 V) than the reference ITO OLED. The lower turn-on voltage and the uniformity of the light output through the gold grid TCE are discussed, and the conduction mechanisms in the ITO and gold grid TCE OLEDs are examined.