[Researcher of the Month] New Technology of Patterning the Perovskite
Professor Kang Young-jong (Department of Chemistry)
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Have you ever seen the integrated circuit in your device? A part of it, which resembles a tiny wafer, is called wafer. Before coming to be a part of our smartphones, laptops, and televisions, the wafer goes under a complex set of procedures, one step of which is lithography, also known as patterning. As the name suggests, lithography is imprinting patterns on a clean film or substrate. The traditional way of doing this is called photolithography, which, simply put, involves placing a photoresist mask with the pattern on top of the wafer and shooting a UV light so that the pattern is etched onto the wafer.
However, there exists a problem with this method. In the field of solar cell and Light Emitting Diode (LED), a material that has been under spotlight for many years for its overpowering efficiency is named perovskite. However, this material is extremely unstable when met with water. Thus, in order to use it, it needs to be surrounded by polymer to make a composite. The problem lies in that the composite is almost impossible to stabilize and pattern using the traditional photolithography. Nevertheless, Professor Kang Young-jong (Department of Chemistry) made this possible, inventing a new patterning technique called, Size-exclusion lithography.
What is Size-exclusion lithography?
What Kang did was coat the wafer with a mixture of two materials, polymer and perovskite. When the wafer is shot with UV light, polymer as well as perovskite nanoparticles are created. The polymer starts to entangle in a chain shape, called a polymer mesh. It first increases in size but soon starts shrinking – on the other hand, perovskite nanoparticles become larger. Consequently, the nanoparticle escapes the polymer mesh and re-arranges itself, arriving at a phenomena called Size-expansion. Using this phenomena, Kang was able to make the pattern arrange by itself on the wafer, without the need of photolithography.
This new technology is significant in many ways. First of all, what was deemed impossible (patterning of perovskite composite) was made possible. Also, since the process of etching is no longer necessary, the wafer-making process will be simpler. Moreover, when it comes to stability, the perovskite composite can edure a full day dipped in boiling water, as it had previously lost its function after only a couple of hours, mid-air.
The remaining task
Although a significant discovery, Kang says there are many more hurdles to jump over for an actual device to be complete. For that reason, there was recently a joining of a professor specializing in such a field, and the team is working together on developing LED using perovskite, ultimately leading to a completion of an actual device. Kang evaluates this finding as “ultimately, a contribution to the development of LED.”
Lim Ji-woo firstname.lastname@example.org
Photos by Park Geun-hyung
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