Luminescent solar collectors: Silicone makes power generation more flexible and colourful

Plastics contribute to climate protection. As fibre-reinforced plastics for wind turbines or films for solar cells, they already play an important role in power generation from renewable energies. But the conventional solutions are not equally suitable for every area of application. This is where a new type of material comes into play that was developed at Saarland University.

In an interview with K-MAG, Prof. Guido Kickelbick talks about the new silicon-like material, its application in luminescent solar collectors and where they could be used specifically.

Prof. Kickelbick, you have been researching flexible, silicone-like materials for several years. What was the goal of your research?

Prof. Dr. Guido Kickelbick: We are fascinated by the excellent thermal and optical properties of flexible, silicone-like materials. So we looked into their application as LED encapsulation materials in a larger project. It turned out that certain chemical boundary conditions of the material have to be fulfilled for organic conversion dyes to be resistant under the extreme conditions on an LED. These dyes, which partially convert the blue light of the LED into red or green light to produce white light, should replace inorganic dyes doped with rare earths. We have also developed completely new silicon-like materials for encapsulating LEDs that could increase the stability of organic dyes on LEDs by orders of magnitude. Thanks to our expertise in synthetic chemistry, we were able to vary many properties such as refractive index and viscosity, which is required in many applications.

In a cooperation with the University of Pisa, a material you developed has now been used for the first time for flexible solar concentrators. What is it all about?

Kickelbick: We met my colleague Prof. Andrea Pucci from the University of Pisa at a conference and he was immediately fascinated by our optical materials because we are able to embed long-lasting and very efficient fluorescent dyes in flexible materials with a long lifetime. Prof. Pucci's research is in the field of luminescent solar collectors (LSC). These are plastics filled with fluorescent dyes. These dyes absorb and emit light, which is repeatedly reflected from the surfaces of the panels into the interior until it reaches the edges. There, the light escapes and can be converted into electricity via photovoltaic elements. Up to now, research has concentrated mainly on hard plastics such as polymethyl methacrylate, also known as Plexiglas. With our polymers, flexible LSCs can now also be created.

What material do you use for this? In what way is it particularly suitable for the LSCs?

Kickelbick: At the moment, we use optical silicones for this application, which have a high refractive index. A dye we developed together with industry builds into the polymer structure when the silicone resin is cross-linked. This increases the stability of the overall system. However, we also succeed in incorporating other dyes. The advantages of the systems used are the high refractive index, which improves the reflection of light at the interface with the air, as well as the high transparency and chemical resistance of the polymers. In addition, we can incorporate very well-established dyes that have a high quantum yield, i.e. that convert as many of the incident light quanta as possible into an emitted light quantum. In the future, we want to use the new systems we have developed, which have even more advantages in terms of processing and durability.

What advantages do the flexible collectors have over conventional components with solid plastic?

Kickelbick: The biggest advantage of flexible systems is their adaptability to different structures on which the solar collectors are then mounted or attached. They are also less brittle, which provides additional protection against mechanical stress.

Where could LSCs be used in the future?

Kickelbick: Due to their very broadly selectable colour, which essentially depends on the accessibility of suitable dyes, luminescent solar collectors can be used as electricity suppliers wherever electricity generation is currently out of the question. For example, I could imagine LSCs as design elements on façades, such as noise barriers or building facades, or as partially transparent roofs.