Hot seat: Prof. Dr. Rubén Darío Costa Riquelme

Last updated on: 07 Oct, 2020

Mr Riquelme, about 25 years ago the first light-emitting electrochemical cells (LECs) were discovered. You have recently published a special issue about these cells in the journal “Advanced Functional Materials” together with Prof. Pei from UCLA. What advantages do LECs have in comparison to the currently used LEDs and when and in which areas will we encounter them for the first time? How will we generate light in 2050? With LEDs or LECs?

First, I would like to mention that there are two types of lighting systems, the inorganic LEDs, and the organic OLEDs and LECs. The organic lighting systems are used e.g., for large lighting surfaces or flexible screens, which is not possible with the inorganic systems.

LECs are the simplest type of organic-based thin-film lighting components so far. They consist of only one active layer in which ionic electrolytes and emitters are combined. They can be produced by spray coating and air-stable electrodes such as AI, Ag or Au can be used. Thanks to this tolerant manufacturing method, we were able, for example, to create light elements on forks, printer paper of items of clothing. However, the ease of use comes at the price of mediocre performance compared to OLEDs. That is why LECs are used more in decoration, signalling or intelligent labelling.

As far as the market launch is concerned, there are currently three start-up companies worldwide that sell so-called electroluminescent inks which are based on the LEC concept. Nevertheless, it is difficult for LECs to compete with the excellent performance of OLEDs or inorganic LEDs. However, these also have their limitations: The production of LEDs, for example, requires rare earths and the recycling of these materials has so far not been very efficient or financially lucrative. This endangers the long-term future of LEDs. OLEDs, on the other hand, have the problem that their production is generally very expensive. It is essential to find solutions to all these challenges in the next few years. In conclusion, I would rather see these three lighting systems complementing each other and less as competitors. Thanks to their different strengths, they are suitable for different applications (house lighting, screens, intelligent labelling, etc.) and thus complement each other. I am convinced that by 2050 we will see improved versions of all three types in our everyday life.

This year you have received the FPdGI Scientific Research Award, congratulations. What research did you win this for? Was that also about LECs?

No, this was about another research topic in my group. As I mentioned earlier, inorganic LEDs require rare earths. The white LEDs that we use in our apartments consist of a blue LED coated with a colour filter made of yttrium, a rare earth metal. The filter partially transforms the blue light into yellowish-orange light and the combination of these results in white light. On our planet there are only 400.000 t of yttrium left and we are currently using 20.000 t per year for the worldwide LED production. This can also be seen in the cost of the filter, which now accounts for 20-30 percent of the total price of an LED. The sustainable future of LEDs in their current form must therefore be classified as very critical. That is why we looked for a solution and introduced so-called bio-LEDs. We are replacing the inorganic colour filter with a filter made of fluorescent proteins. This idea was already proposed in the year 2000, but at that time it was concluded that it is impossible to stabilize proteins outside of water. The LED technology, however, does not accept water. The question of how these proteins could be used for our technology remained open until, in 2015, we discovered a new family of polymers in which the fluorescent proteins remained stable for months and even years even under the operating conditions in an LED. Since our first bio-LED prototype, we have focused on understanding how proteins are stabilized, which polymer designs are the best, whether we can develop fluorescent proteins ourselves, how we can use this material in other technologies, and what the actual effects of this hybrid technology are for our future. This award highlighted all our contributions so far. I am very pleased that there is much more to research in this area.

One of the main missions of Chemie-Cluster Bayern’s Contact Offices is to bring together research and industry. What challenges would you like to tackle in cooperation with an industrial partner in the future?

There is still a lot to do in the development of sustainable technologies. Toxic and resource-scarce materials in today’s technologies need to be replaced by sustainable materials. This is one of the most urgent challenges that our technological society is facing. The industry is an important driving force here which has the power to turn something into reality in order to create a better future for the next generations.

From our side, we can only make suggestions e.g., to increase the value of commercial potting materials (polymers, silicones, etc.), paints (electroactive inks, additives, etc.) and energy-related components (lighting and photovoltaics) by means of biological materials such as fluorescent proteins and enzymes. However, our laboratory expertise can only reach its full potential in cooperation with the industry. Therefore, I am always happy to discuss various scenarios for new materials or applications with industrial partners in order to enable a better future.

Prof. Costa completed his master’s degree in chemistry in 2006 and received his doctorate (Uni Valencia, IcMol) in 2010 as well as several national and international awards. From 2011 to 2013 he was as a Humboldt Fellow at the University Erlangen-Nürnberg (FAU), where he researched nanocarbon-based solar cells. In 2014 he was head of the Hybrid Optoelectronic Materials and Components laboratory at FAU. In 2017 he moved to IMDEA Materials (Spain) and as an associate professor at the University of Waseda (Japan) expanded his team. Since 2020 Prof. Costa has been a full professor for “Biogenic Functional Materials” at TUM. His research ranges from the development and manufacture of bio-hybrid materials to the manufacture and optimization of optoelectronic components for energy applications (lighting / photovoltaics) and medical benefits (sensor technology / therapy). His long-term goal is to meet the “green photonics” concept with his optoelectronic components.