Fantastic light with minimal voltage

Luminous electrochemical cells (LECs) allow you to develop low-cost, easy-to-manufacture lighting technology. Such cells are thin film electronic and ionic devices that produce light when a low voltage is applied. Researchers have now used comprehensive data analysis to create first-class electrochemical cells from copper complexes that emit blue and white light, says the Technical University of Munich in a press release.

Light-emitting electrochemical cells (LECs) are the simplest and most cost-effective thin film lighting devices available to date. They consist of a single active layer. They are used, for example, for so-called electroluminescent inks and stickers.

Electroluminescence

The effect of electroluminescence was first demonstrated in 1905. At that time, two researchers discovered the presence of light under applied stress in various minerals and metals and were able to correlate the intensity with stress and heat evolution.

Their prototypes are considered to be the first light emitting diodes (LEDs). “However, technical use of the effect only became possible later. More well-known than the LECs we look at are LEDs – semiconductor devices that also emit light when an electrical voltage is applied to them. But LECs follow a different principle, ”explains Rubén D. Costa, professor at TUM.

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The research groups of prof. Dr. Rubén D. Costa from TUM Campus Straubing for Biotechnology and Sustainability and Prof. Claudia Barolo from the University of Turin has now developed the first approach to the development of LEC emitters and so-called active layers, creating excellent blue and white LECs based on copper (I) complexes.

“Blue light is needed to develop low-cost devices that emit white light. However, the previous lack of blue emitters prevented the transition from the laboratory to the real market. The production of blue emitters is therefore a milestone in thin film lighting. Once the blue units are there, we can relatively easily produce white units, ”says Prof. cost.

Emission color

And it is precisely this generation of blue transmitters that the research groups have now achieved. The research groups from Straubing and Turin have successfully used computer science tools to establish a statistical relationship between the X-ray structure and the electronic characteristics of copper (I) complexes with dimin and diphosphine ligands.

At the same time, they examined the structural and electronic parameters and their interrelationships to determine the emission color, efficiency, and luminescence of the devices. After extensive evaluation of data from several known approaches, a new design has emerged for blue LECs with excellent performance compared to devices with conventional emitters.

White LECs

“With the new high-performance blue LECs, single-layer white LECs based on copper (I) can be realized with a high-quality white color with a color rendering index of 90,” says Prof. Claudia Barolo from the University of Turin. The color rendering index can assume a maximum value of 100. It indicates what natural colors of illuminated objects look like under a particular light source. With a value of 90, it is already very good. This work demonstrates a new way of streamlining the design of emitters and active layers in thin film lighting. “We are convinced that our analysis model is a first step towards advanced machine learning methods to fine-tune other active compounds as well,” explains Costa.

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