Wednesday, November 14, 2012

[Ru(bpy)3](BF4)2 for OLEDs

A coordination complex between a transparent tin oxide electrode and an active metal electrode produces light when an external voltage is supplied. Frabrication of OLEDs is a art, beacause you need perfectly spin-coater control and the right materials. In this post I compiled from diferent web sites and articles how to get OLEDs with [Ru(bpy)3](BF4)2 in thin layers between two conductin glass electrodes. 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. to prepare [Ru(bpy)3](BF4)2: 1. Measure 0.083 g (to the nearest 0.001 g) of the dried RuCl3 (MM = 207.45 g) in a 30mL beaker and place a stirbar in it. 2. Add 8 mL of water to the beaker, clamp it to a ring stand, and place beaker on top of a heater/magnetic stirrer. Turn the heat on ~ 5 and start mixing the solution. 3. In a weigh boat, measure 0.188 g (to the nearest 0.001 g) of 2,2’dipyridyl (MM = 156.19 g) and add to the beaker. 4. Use a micropipette to measure out 440 mL of NaH2PO2 into the beaker. Cover with a watch glass to prevent evaporation, and mark the initial water level on the outside of the beaker with a permanent marker. 5. Reflux the solution for 30 minutes. If the solution starts to bubble too rapidly, turn down the variac. During this time, check the water level every 5 minutes or so, and add additional water to maintain volume if necessary. After [Ru(bpy)3](BF4)2 synthesis get a cunductive glass pieace and 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 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. 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.
from : Preparation of an Organic Light Emitting Diode Adapted by Jessica A. Kufs and Raymond D. Baechler, Ph.D.

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