Highly efficient blue organic light-emitting devices with indium-free transparent anode on flexible substrates

Indium-free transparent conducting oxides (TCOs) may provide a lower cost solution for the transparent anode in large area displays and solid-state lighting. Low temperature deposition processes are essential for manufacturing compatible with flexible substrate materials. We report herein a near room temperature sputtering process for generating an indium-free TCO coating on a flexible substrate. Specifically, we deposited gallium-doped zinc oxide (GZO) uniformly over a 12″ diameter area at nominally room temperature on polyethylene terephthalate (PET), without any noticeable damage to the PET substrate. The GZO films exhibit excellent physical, optical and electrical properties: roughness ∼7 nm, transmittance >85% and resistivity ∼10−3 ohm cm. Phosphorescent blue organic light-emitting devices (OLEDs) were fabricated on these substrates with comparable performance (16% external quantum efficiency and 33 lm/W power efficiency at 1 mA/cm2) to that of devices fabricated on glass with GZO or indium tin oxide (ITO) as the anodes. These results demonstrate the utility of using GZO instead of the higher cost material ITO on PET for flexible displays and solid-state lighting.