Zinc oxide is an n-type semiconductor for the LED's substrate with p-type copper oxide for connecting to its surface electrode.
Here is what Linkoping University says about white paper LEDs: Imagine a white luminous curtain waving in the breeze. Or wallpaper that lights up your room with perfect white light. In his doctoral thesis, Gul Amin shows how white LEDs can be manufactured directly on paper.
Gul Amin, who recently received his doctorate at the Physical Electronics and Nanotechnology group, Campus Norrköping, shows in his thesis how it is possible to grow white LEDs, made from zinc oxide and a conducting polymer, directly on a piece of paper. He also shows how they can be printed onto wallpaper, for example - a method with a patent pending.
His research colleague, Naved ul Hassan Alvi, looked at his thesis from last summer at various methods for producing - growing - different nanostructures of zinc oxide on a number of different semiconducting materials.
Nanostructures of zinc oxide have a number of characteristics that make them suited to the manufacture of white LEDs - among them a large band gap and electrons that move easily and give off relatively large amounts of energy once they have bounced back towards the nucleus. Plus the fact that the energy is emitted as perfect white light.
Gul Amin has now gone further and succeeded in growing white LEDs directly on paper. The active components are nanothreads of zinc oxide on a thin layer of polydiethylflourene (PFO), a conducting polymer. But the paper has first been coated with a thin, water-repellent, protective and levelling layer of cyclotene, a resin.
“This is the first time anyone has been able to build electronic and photonic inorganic semiconducting components directly on paper using chemical methods,” says professor Magnus Willander, who is leading the research.
The article has been published in Wiley’s physica status solidi - Rapid Research Letters.
In one of the thesis’ other articles, published in Springer’s Journal of Material Science, Gul Amin also shows how it is possible to grow nanothreads on paper, blow them off the surface using ultrasound and collect them in the form of a powder.
This powder can then be used to print the nanothreads of zinc oxide, and thus LEDs, on paper or plastic in a normal printing press. That method also has patents pending, with an application by Gul Amin along with the Ecospark firm, founded by Magnus Willander, and Acreo.
Since zinc oxide is a natural semiconductor of the n type (surplus negative charge), which is due to defects in the material, Gul Amin also combined zinc oxide with copper oxide, which is of the p type (surplus positive charge), to create a few different types of electrochemical sensors.
Following his doctorate, Gul Amin returned to his native Pakistan to pursue his research, but at the Physical Electronics and Nanotechnology group the potential of zinc oxide is being further explored, in combination with graphene, copper oxide and other materials.