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Published: 2019-11-25

Bright and efficient light without rare metals

NEWS Modern smartphone displays, as well as many other efficient light sources, contain costly and environmentally problematic rare metals. For a sustainable future, we must turn to sustainable materials. Researchers at Umeå and Kyushu University show that such materials are practical alternatives for efficient light-emitting electrochemical cells. The results are published in Nature Communications.

Text: Ingrid Söderbergh

Artificial light surrounds us, both in the form of lighting and displays. As of now, organic light-sources are entering the market, and with them, we foresee the emergence of new light-emitting applications: spanning from medical diagnostics to electronic-textiles. In this aspect, the light-emitting electrochemical cell (LEC) is a rising star. It is a super thin and flexible light-source, which allows for cheap and upscaleable — “newspaper-like” — manufacturing.

Unfortunately, today’s most efficient LECs, similar to many other light-sources, contain rare metals, such as iridium. This makes them expensive and environmentally problematic. To fabricate purely organic light-sources that are efficient in transforming electricity into light, and at the same time cheap and recyclable is a challenge.

Encouragingly, we make headway with the newly developed group of completely organic light-emitting materials, which match the efficiency of the rare-metal based ones. These materials have already shown promising results when incorporated in complex high-end devices. However, when included in the less complicated and hence cheaper LEC, their performance have not impressed. Until now!

A recent study carried out by physicists at Umeå University, in collaboration with Kyushu University; demonstrate that bright and efficient light is achievable from LEC based on such organic light-emitting materials.

By understanding and making use of the LECs distinguishing features, such as the electrochemical doping, we have shown that these environmentally greener materials are a practical alternative also in LECs.

– The LEC may have a simple device design, but the dynamics that occur in that thin film and enables light-emission is involved. It is a sophisticated interaction between organic semiconductors and mobile ions, which have to be balanced in order to attain bright and efficient light. The efficiency of light-emitting materials depends highly on their nanoscopic surrounding, and it is with that in mind we were able to boost their performance, says Petter Lundberg, lead author and doctoral student at the Department of Physics, Umeå University.

Petter Lundberg is a Ph.D. student at the organic photonic and electronics group, led by Professor Ludvig Edman, at the Department of Physics. The main focus of the group is the light-emitting electrochemical cell. The group works on improving the understanding of how the LEC work, and by that e.g. improving device efficiency and facilitate upscalable manufacturing.

Learn more about the Organic Photonics and Electronics Group at Umeå university

Press material:

Eight press photos. Credit Mattias Pettersson / Mattias Lindh

Original article:

P. Lundberg, Y. Tsuchiya, E.M. Lindh, S. Tang, C. Adachi and L. Edman: Thermally Activated Delayed Fluorescence with 7 % External Quantum Efficiency from a Light-Emitting Electrochemical Cell. Nature Communication 10. 5307 (2019). doi. 10.1038/s41467-019-13289-w