Michael Helander’s light emitting diode is simpler and potentially cheaper to manufacture than existing versions.
By Tyler Irving
Posted June 2011
Organic light emitting diodes (OLEDs) can replace liquid crystal displays (LCDs) in such things as cell phones but, due to their complexity, are costly to produce. This could soon change, thanks to an accidental discovery by Michael Helander, a graduate student in the University of Toronto’s Department of Materials Science & Engineering.
OLEDs are made of thin films of luminescent organic molecules sandwiched between two electrodes. When properly arranged and supplied with an electrical current, they can produce a full-colour, flat panel display. The upper surface is made of indium tin oxide (ITO), which is both electrically conductive and partially transparent. This design is problematic however, as there is a gap between the energy needed to remove an electron from the organic layer and the energy required for the ITO to accept it. Current designs bridge this gap using additional layers of transparent organic materials, but each layer adds enormously to the cost of production.
Helander hit on a unique approach after noticing that the efficiency of one of his experimental batches of OLEDs was unexpectedly high. X-ray photoelectron spectroscopy revealed traces of chlorine on the ITO surface. “We were baffled,” says Helander. “Where was this coming from? Then we realized that someone in the lab had solvent bottles open.” Fumes from the chlorinated solvents, reacting with the ultraviolet light used to clean the ITO, had deposited a thin layer of indium chloride on the ITO surface. This allowed the ITO to accept lower energy electrons. The result was an OLED that works at high efficiency without the need of additional organic transport layers.
“People tried to do this years ago,” says Helander. “The problem was that most forms of chlorine are highly reactive and tend to etch away ITO. The breakthrough here was to start with a relatively inert chlorine-containing organic compound.” Helander hopes the innovation will make OLEDs more competitive with LCD technology.
Photo Credit: Michael Helander
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