Hannah Bürckstümmer
1,424,022 views • 10:15

You may have noticed that I'm wearing two different shoes. It probably looks funny — it definitely feels funny — but I wanted to make a point. Let's say my left shoe corresponds to a sustainable footprint, meaning we humans consume less natural resources than our planet can regenerate, and emit less carbon dioxide than our forests and oceans can reabsorb. That's a stable and healthy condition. Today's situation is more like my other shoe. It's way oversized. At the second of August in 2017, we had already consumed all resources our planet can regenerate this year. This is like spending all your money until the 18th of a month and then needing a credit from the bank for the rest of the time. For sure, you can do this for some months in a row, but if you don't change your behavior, sooner or later, you will run into big problems.

We all know the devastating effects of this excessive exploitation: global warming, rising of the sea levels, melting of the glaciers and polar ice, increasingly extreme climate patterns and more. The enormity of this problem really frustrates me. What frustrates me even more is that there are solutions to this, but we keep doing things like we always did. Today I want to share with you how a new solar technology can contribute to a sustainable future of buildings.

Buildings consume about 40 percent of our total energy demand, so tackling this consumption would significantly reduce our climate emissions. A building designed along sustainable principles can produce all the power it needs by itself. To achieve this, you first have to reduce the consumption as much as possible, by using well-insulated walls or windows, for instance. These technologies are commercially available. Then you need energy for warm water and heating. You can get this in a renewable way from the sun through solar-thermal installations or from the ground and air, with heat pumps. All of these technologies are available.

Then you are left with the need for electricity. In principle, there are several ways to get renewable electricity, but how many buildings do you know which have a windmill on the roof or a water power plant in the garden? Probably not so many, because usually, it doesn't make sense. But the sun provides abundant energy to our roofs and facades. The potential to harvest this energy at our buildings' surfaces is enormous. Let's take Europe as an example. If you would utilize all areas which have a nice orientation to the sun and they're not overly shaded, the power generated by photovoltaics would correspond to about 30 percent of our total energy demand.

But today's photovoltaics have some issues. They do offer a good cost-performance ratio, but they aren't really flexible in terms of their design, and this makes aesthetics a challenge. People often imagine pictures like this when thinking about solar cells on buildings. This may work for solar farms, but when you think of buildings, of streets, of architecture, aesthetics does matter. This is the reason why we don't see many solar cells on buildings today. They just don't match.

Our team is working on a totally different solar-cell technology, which is called organic photovoltaics or OPV. The term organic describes that the material used for light absorption and charge transport are mainly based on the element carbon, and not on metals. We utilize the mixture of a polymer which is set up by different repeating units, like the pearls in a pearl chain, and a small molecule which has the shape of a football and is called fullerene. These two compounds are mixed and dissolved to become an ink. And like ink, they can be printed with simple printing techniques like slot-die coating in a continuous roll-to-roll process on flexible substrates. The resulting thin layer is the active layer, absorbing the energy of the sun. This active layer is extremely effective. You only need a layer thickness of 0.2 micrometers to absorb the energy of the sun. This is 100 times thinner than a human hair. To give you another example, take one kilogram of the basic polymer and use it to formulate the active ink. With this amount of ink, you can print a solar cell the size of a complete football field. So OPV is extremely material efficient, which I think is a crucial thing when talking about sustainability.

After the printing process, you can have a solar module which could look like this ... It looks a bit like a plastic foil and actually has many of its features. It's lightweight ... it's bendable ... and it's semi-transparent. But it can harvest the energy of the sun outdoors and also of this indoor light, as you can see with this small, illuminated LED. You can use it in its plastic form and take advantage of its low weight and its bendability. The first is important when thinking about buildings in warmer regions. Here, the roofs are not designed to bear additionally heavy loads. They aren't designed for snow in winter, for instance, so heavy silicon solar cells cannot be used for light harvesting, but these lightweight solar foils are very well suited. The bendability is important if you want to combine the solar cell with membrane architecture. Imagine the sails of the Sydney Opera as power plants. Alternatively, you can combine the solar foils with conventional construction materials like glass. Many glass facade elements contain a foil anyway, to create laminated safety glass. It's not a big deal to add a second foil in the production process, but then the facade element contains the solar cell and can produce electricity.

Besides looking nice, these integrated solar cells come along with two more important benefits. Do you remember the solar cell attached to a roof I showed before? In this case, we install the roof first, and as a second layer, the solar cell. This is adding on the installation costs. In the case of integrated solar cells, at the site of construction, only one element is installed, being at the same time the envelope of the building and the solar cell. Besides saving on the installation costs, this also saves resources, because the two functions are combined into one element.

Earlier, I've talked about optics. I really like this solar panel — maybe you have different taste or different design needs ... No problem. With the printing process, the solar cell can change its shape and design very easily. This will give the flexibility to architects, to planners and building owners, to integrate this electricity-producing technology as they wish.

I want to stress that this is not just happening in the labs. It will take several more years to get to mass adoption, but we are at the edge of commercialization, meaning there are several companies out there with production lines. They are scaling up their capacities, and so are we, with the inks.

(Shoe drops)

This smaller footprint is much more comfortable.


It is the right size, the right scale. We have to come back to the right scale when it comes to energy consumption. And making buildings carbon-neutral is an important part here. In Europe, we have the goal to decarbonize our building stock [by] 2050. I hope organic photovoltaics will be a big part of this.

Here are a couple of examples. This is the first commercial installation of fully printed organic solar cells. "Commercial" means that the solar cells were printed on industrial equipment. The so-called "solar trees" were part of the German pavilion at the World Expo in Milan in 2015. They provided shading during the day and electricity for the lighting in the evening. You may wonder why this hexagonal shape was chosen for the solar cells. Easy answer: the architects wanted to have a specific shading pattern on the floor and asked for it, and then it was printed as requested. Being far from a real product, this free-form installation hooked the imagination of the visiting architects much more than we expected.

This other application is closer to the projects and applications we are targeting. In an office building in São Paulo, Brazil, semitransparent OPV panels are integrated into the glass facade, serving different needs. First, they provided shading for the meeting rooms behind. Second, the logo of the company is displayed in an innovative way. And of course, electricity is produced, reducing the energy footprint of the building.

This is pointing towards a future where buildings are no longer energy consumers, but energy providers. I want to see solar cells seamlessly integrated into our building shells to be both resource-efficient and a pleasure to look at. For roofs, silicon solar cells will often continue to be a good solution. But to exploit the potential of all facades and other areas, such as semitransparent areas, curved surfaces and shadings, I believe organic photovoltaics can offer a significant contribution, and they can be made in any form architects and planners will want them to.

Thank you.