Researchers 'paint' Marie Curie in a semiconductor layer

Imagine that you could paint a canvas by making the canvas itself change to a different colour instead of brushing paint on it. That is exactly what Lukas Helmbrecht and his colleagues at Amsterdam research institute AMOLF are doing, thanks to a new technique called ion exchange lithography — which takes on the fundamental challenge of patterning semiconductor materials with different properties in a single film. This patterning is essential for the development of next‐generation (opto)electronic functional components such as LEDs or solar cells.

The concept of the technique is to use a reactive ‘ink’ that can be painted or printed on an equally reactive ‘canvas’, after which a perovskite semiconductor forms by means of ion exchange. As a proof of principle, the researchers used the technique to airbrush a portrait of Marie Curie in a perovskite semiconductor layer, with the results described in the journal Advanced Materials.

Perovskite is a highly promising semiconductor material used to produce items such as LEDs and solar cells. Helmbrecht and colleagues found a way of converting a layer of lead carbonate (the canvas) into a perovskite, simply by ‘painting’ on it with a solution of methylammonium bromide. The latter undergoes a chemical reaction with the lead carbonate to form a green-emitting perovskite. Using a solution of a different substance as the ink allows you to paint a blue- or red-emitting perovskite next to this, or to airbrush or print a pattern.

A wide range of variations in the composition of the perovskites is possible by choosing different inks, and the patterns can be created very accurately: drops of ink just a few micrometres in size also yield dots just a few micrometres in size. This means the ink does not run.

“The challenge of this research was developing the chemical reaction and the conditions: the quantity of ink, the pressure and the properties of the canvas,” said Helmbrecht. “None of these was known, and the process does not work if they are not exactly right.”

Helmbrecht said ion exchange lithography is fundamentally different from existing techniques for depositing perovskite layers, noting, “All traditional techniques result in different layers of different perovskites. Our method results in one single layer that consists of different types of perovskite.”

In addition, perovskites are usually quite sensitive to the treatments used in traditional methods, such as etching or rinsing, which can damage the perovskite. With ion exchange lithography, such treatments are no longer needed, and cleanrooms or other special conditions are no longer required.

“We have developed a far simpler method for applying a pattern of different perovskite semiconductors next to each other on a chip or LED,” Helmbrecht said.

The researchers have already demonstrated the utility of ion exchange lithography by using the technique to produce a working LED, which Helmbrecht said has proven the principle. Different groups within AMOLF will now start using the technique to create other applications.

Image caption: Perovskite portrait of Marie Skłodowska Curie. Image credit: Lukas-Helmbrecht.

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