A group of chemists led by Emory University professor Letian Dou has discovered a hidden mechanism in the process of creating perovskite-based light-emitting diodes (LEDs), a hybrid material combining organic and inorganic molecules. The results, published in the journal Nature, make it possible to raise the efficiency of converting electricity into light from the typical 20-30% to almost 40%.
"Our discovery leads to an efficiency close to 40%. This is a big leap," the university press release quoted Dou as saying. Perovskite LEDs are seen as promising for biomedical sensors, low-light imaging and automatic facial recognition.
The key to the improvement turned up by accident. First author Song-Du Baek, working as a postdoc in Dou's laboratory, noticed that one batch of devices showed an efficiency of about 30% instead of the expected 20-25%. At first he checked whether oxygen was leaking into the glovebox (a sealed chamber with purified nitrogen where samples are assembled), but that version was not confirmed. The researcher then decided to study the chemistry of the solution itself.
After months of experiments it emerged that it all comes down to the solution heating time. The optimum turned out to be 20 minutes. With such a hold, a linear compound that boosts LED efficiency forms more actively, and the formation of a ring compound that lowers it is suppressed. The scientists then synthesized and purified the linear compound and developed a method of controlling the reaction pathway, which made it possible to raise peak efficiency to 37%.
"What surprised me most is that even a detail that seems trivial can matter so much," co-author Yu-Ting Yang noted.
Scientists from Purdue University, the University of Michigan and Princeton University also took part in the work. The authors stress that this is a laboratory result, not a finished commercial product. They plan to continue raising the efficiency and service life of perovskite LEDs, as well as to demonstrate their applicability in biomedical research.