Preparation of an Organic Light Emitting Diode

Modification by Jason Marmon, George Lisensky, and Wendy deProphetis from Frank G. Gao and Allen J. Bard, "Solid-State Organic Light-Emitting Diodes Based on Tris(2,2'-bipyridine)ruthenium(II) Complexes," Journal of the American Chemical Society, 122(30), 7426-7427 (2000) and Hannah Sevian, Sean Muller, Hartmut Rudmann, and Michael F. Rubner, "Using Organic Light-Emitting Electrochemical Thin-Film Devices to Teach Materials Science," Journal of Chemical Education, 81(11), 1620 (2004).

A coordination complex between a transparent tin oxide electrode and an active metal electrode produces light when an external voltage is supplied. Too thin a coating of the [Ru(bpy)3](BF4)2 polyvinylalcohol layer will give a short circuit and no light; too thick a coating will have a large electrical resistance and no light.

Procedure

Wear eye protection

Chemical gloves recommended

Identify the conducting side of a tin oxide-coated piece of glass by using a multimeter to measure resistance. The conducting side will have a finite resistance of 20-30 ohms.

Use double-stick tape to attach indium-tin oxide glass with the conductive. Remove fingerprints from the glass.
Use a cotton applicator to spread a layer of [Ru(bpy)3](BF4)2 polyvinylalcohol solution on the center of the glass. Surround with a splatter shield and spin at 2500 rpm for 10-60 seconds. Repeat for a total of 3-4 applications, trying to keep some uncoated regions at the edges.

Instead of using the preferred spin coating method in the previous step, use double-stick tape to attach indium-tin oxide glass with the conductive side up to the benchtop. Use a cotton applicator to spread a very thin layer of [Ru(bpy)3](BF4)2 polyvinylalcohol solution on the glass. Evaporate using a heat gun or hair drier. Repeat for a total of 3-4 applications, trying to keep some uncoated regions at the edges.

Obtain a template mask or prepare one using a piece of duct tape on aluminum foil and punching a 2/16 inch hole.

Remove any remaining moisture in the film by heating for at least a minute in a hair drier. The primary reason for failure of oLEDs to light is insufficient drying of the polymer layer before adding the active metal layer.

Use a cotton swab to paint through the template with liquid gallium-indium alloy to add an active metal electrode. (This eutectic mixture of 75.5% gallium and 24.5% indium is a liquid above 16.5 degrees centigrade.)

Touch the positive lead of a 4.5-volt power supply to the tin-oxide glass (not the [Ru(bpy)3](BF4)2 coating). Gently touch the negative lead to the gallium-indium. In humid environments the lifetime is greatly shortened.

View from under the indium-tin oxide glass (left) or view in the dark (right).

Is the circuit a diode? What happens if you reverse the polarity of the applied voltage?

Conclusions

  1. How many layers of the [Ru(bpy)3](BF4)2 polyvinylalcohol solution did you apply? What would you recommend?
  2. How many gallium-indium dots did you apply? How many of them could be made to give off light?
  3. How does the circuit produce light? Draw an energy level diagram to illustrate your answer.
  4. Is the circuit a diode? How do you know?

Materials