A coordination complex between a transparent tin oxide electrode and an active metal electrode produces light when an external voltage is supplied.
- Wear eye protection
- Chemical gloves recommended
Step 1. 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.
Step 2. Use double-stick tape to attach indium-tin oxide glass with the conductive. Remove fingerprints from the glass.
Step 3. 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.
Step 4. Obtain a template mask or prepare one using a piece of duct tape on aluminum foil and punching a 2/16 inch hole.
Step 5. 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.
Step 6. 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.)
Step 7. 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?
- How many layers of the [Ru(bpy)3](BF4)2 polyvinylalcohol solution did you apply? What would you recommend?
- How many gallium-indium dots did you apply? How many of them could be made to give off light?
- How does the circuit produce light? Draw an energy level diagram to illustrate your answer.
- Is the circuit a diode? How do you know?
Stock Solutions for multiple preparations.
- Place approximately 0.30 g PVA (polyvinyl alcohol, Aldrich, 36,316-2, Average MW 124,000-186,000) and 10 mL of water in a 30-mL beaker. Cover the beaker with a watch glass or loosely with plastic wrap. Dissolve the PVA by heating the mixture in a microwave for 5-15 second increments. Do not allow the solution to boil. Stirring with a glass rod may help
- Dissolve approximately 0.035 g [Ru(bpy)3](BF4)2 (Synthesis) in 3 mL of polyvinylalcohol solution.
- GaIn Eutectic, Aldrich, 49542-5
- Conductive Glass (1″ x 1″ x 2.3mm TEC 15 glass), Hartford Glass Co, 735 E Water Street, Hartford City, IN 47348 Phone: 765-348-1282
- 2500 rpm fan and power supply, Radio Shack 273-243B 12VDC Cooling Fan, 273-1662 Universal Power Adapter
- Double-stick tape
- Template masks made from aluminum foil, duct tape, 2/16″ hole punch
- Cotton swabs
- Hair dryer
- 4.5-Volt power supply