Just imagine painting a canvas by making that canvas itself change to a different color rather than brushing paint on it. That is exactly what Lukas Helmbrecht, and his colleagues accomplish by means of this new ion exchange lithography technique. In this method, the ‘ink’ reacts with the ‘canvas’ through the ingenious use of ion exchange. Helmbrecht put his mouth where the money is; he airbrushed an image of Madame Curie, using this technique. Let us decode the mystery paint-on semiconductors.
Principle
In principle, this is by far easier than applying a patterned arrangement of disparate perovskite semiconductors side-by-side on a chip or LED. No cleanrooms or special conditions are required anymore. Thus, researchers have managed to demonstrate the applicability of ion exchange lithography by demonstrating the fabrication of an LED using this technique.
The Making
This project is all about making perovskite, a new and very promising semiconductor material for applications such as LEDs and solar cells. We are able to convert a layer of lead carbonate, the actual canvas, into a perovskite by “painting” it with a solution of methylammonium bromide-the methylammonium bromide reacts with the lead carbonate, and you have a green-emitting perovskite. Now you could use this ink to paint in an adjacent blue or red-emitting perovskite, or airbrush or print a pattern.
Result
Different inks lead to a wide range of variations in compositions in the perovskites. One can make the pattern very accurate: drops of ink just a few microns in size yield droplets a few microns in size. That means the ink does not run. “The thing that was the difficulty in this research was developing the chemistry and the conditions: the quantity of ink, the pressure and the properties of the canvas. None of these were known and the process does not work if they are not exactly right.
This brings to mind all other techniques for applying layers of perovskites on a carrier. But that technique is fundamentally different. All traditional techniques mean that perovskites end up beside each other or on top of each other. This method results in one layer of different kinds of perovskite. Moreover, usual treatments would be quite sensitive for perovskites, such as etching or rinsing, procedures that cause damage to the perovskite. Ion exchange lithography is a technique that does not involve these treatments.
Advantage
When the other techniques that were compared to perovskite layering onto the carrier. However, this technique altogether differs from that. All other traditional techniques will produce different layers of perovskite next to each other or on top of each other. This method produces one single layer consisting of different types of perovskites. In addition to this, perovskite is quite much disturbed by treatment. As in the case of etching and rinsing, damaging or sometimes destroying the perovskite itself. Ion exchange lithography removes the necessity for this treatment.
The scientists are into these new properties discovered over the last few months in these semiconductors. They believe that with more research to manage them, one could potentially turn these properties into a simple effective source of light. This might just be the beginning of everything these paint-on semiconductors can do for mankind.
