Discovery of ‘hidden mechanism’ boosts hybrid LED efficiency

Chemists have discovered a method to greatly enhance the performance of hybrid light-emitting diodes (LEDs) made using perovskite. The breakthrough was published in the journal Nature, and holds potential for a variety of applications, including biomedical sensing, low-light imaging, and facial recognition. Most previous research on perovskite LEDs has resulted in quantum efficiency rates, or the ability to convert electricity into light, ranging between 20 and 30%.

According to Letian Dou, senior author and chemistry professor at Emory University, "Our discovery leads to an efficiency rate closer to 40%. That's a big jump." Sung-Doo Baek, the paper's first author, explains that his work as a postdoctoral fellow in Dou's lab led to the discovery of "hidden mechanisms" in the solution used to create these devices that had been previously overlooked.

The insight allowed the researchers to improve the synthesis process, increasing the yield of a compound that boosts LED efficiency while minimizing the production of a compound that hinders it. Co-first author Yu-Ting Yang, a PhD candidate in the Dou lab, notes that even seemingly minor details can have a significant impact. The study's coauthors include scientists from Emory, Purdue University, the University of Michigan, Ann Arbor, and Princeton University.

The researchers aim to find ways to generate light more efficiently at a low cost. In the 2010s, LEDs made from inorganic semiconductors, such as gallium nitride, largely replaced incandescent lightbulbs in households. Inorganic LEDs are efficient, stable, and long-lasting, but they are difficult to assemble into large-area displays or into extremely small pixels, and are rigid, making them more challenging to incorporate into flexible devices and some other applications.

Organic-molecule LEDs are thinner, more flexible, more customizable, and produce more brilliant colors in displays, but they are currently more expensive to produce and less efficient and durable than inorganic LEDs. Dou's lab focuses on developing hybrid LEDs made of metal-halide perovskite, a material that combines organic and inorganic molecules.

These LEDs are lightweight, flexible, and low-cost, with high durability and efficiency in the near-infrared region. Perovskite LEDs have important applications in the near-infrared region, including facial recognition on cell phones, night-vision cameras, and biomedicine for clear, non-invasive imaging of tissues. To improve perovskite LED efficiency for commercial applications, the Dou lab focused on enhancing the synthesis process.

During experimentation, Baek noticed a variation in efficiency rates between batches. After ruling out oxygen as a factor, the team investigated the chemistry of the solution. They discovered that the duration of heating significantly impacted efficiency. Heating for 20 minutes produced the optimal result, as it favored the formation of a linear compound that enhances LED efficiency while suppressing the formation of a ring compound that harms it.