How solar paint could bring clean energy into more places than ever before

Looking to transition to renewables and help fight climate change? While going green today involves installing bulky solar panels, the building of tomorrow could power up with a can of paint.

“Painted-on solar panels” may sound like a complaint about a property scam, but ditching the silicon could lead to cheaper, more convenient, more eco-friendly solar energy.

Wai-Lun Chan, an associate professor of physics and astronomy at the University of Kansas and a researcher in this area, tells Inverse that solar panel prices would drop dramatically.

“If we could do that, we could really drive the cost down, because you don’t need an expensive machine to manufacture this kind of solar panel,” Chan says.

Traditional photovoltaic solar has seen an incredible drop in price over the past decade, but it’s still relatively rare. MIT research shows that solar has dropped in price 99 percent over the past 40 years.

Technologies that make solar cheaper and easier to install could encourage more to make the switch. Imagine the housebuilder of the future planning out a property, realizing that they can add a solar-collecting wall to the side of their house for little added cost. Why not, right? Scale up that logic, and the otherwise-barren sides of giant buildings could harness their sunlight to paint a brighter future for the world. The cost of solar might be a no-brainer, but it could become even more practical too.

It’s one of a number of ideas that could help propel solar technology from conscious construction decision to something that’s practically a no-brainer. Tesla’s Solar Roof is one of a number of products looking to hide the cells as part of an existing construction, in this case something that looks like a regular roof. Other areas of research include origami solar blinds, translucent panels ideal for windows, and heat-storing panels that could also heat water.

These products can open up new chances to go solar, but what if it was as simple as a lick of paint?

Paint-based solar: how to paint a greener future

Paint-based solar is an idea that’s been under research for some time. Researchers at the University of Buffalo announced in 2013 that they had made progress using plasmonic-enhanced materials. The team noted, however, that the thin nature of paint makes absorbing as much light difficult.

A team of Australian researchers demonstrated solar paint back in June 2017 that splits water particles to harness the hydrogen. Torben Daeneke, a research fellow at the Royal Melbourne Institute of Technology, told Inverse at the time that solar paint “might be used alongside traditional solar cells, potentially coating areas that receive too little light to be viably covered with expensive solar cell modules.” He warned, however, that the idea probably wouldn’t come to market for another five years.

Chan has been working with other researchers at the University of Kansas to explore how to use organic semiconductors to produce photovoltaic solar cells.

How does Chan’s research lead to solar paint? Because unlike silicon-based designs, which use brittle wafers to conduct the electrons and move them through the material, these organic materials can be dissolved into a liquid. Once you’ve reached that stage, you have a bucket of electron-conducting material ready for slapping onto all sorts of surfaces.

A solar panel is essentially three layers, two electrode layers and a semiconducting layer. As organic materials enable all three to be dissolved down, it would be a case of layering it up and then wiring it to a system to harness its energy.

The research, published in July in the Journal of American Chemical Society, could enable people to produce solar panels using a printer — or even by painting one on a wall using a special paint — all using a material that’s easier to manufacture and could prove cheaper than silicon.

Chan, one of the paper’s authors, tells Inverse that chemists may be able to pick up their ideas to “synthesize a similar material, so those could be used for painting, or to produce a practical solar panel.”

Chan is unsure that people will paint directly onto the side of the building, perhaps using a plastic layer over the top to reduce the roughness of the building’s materials. But with solar paint can in hand, don’t underestimate the ingenuity of DIY enthusiasts to come up with some special designs.

Paint-based solar: how new research could paint the way to paint-based solar

Chan’s team at the University of Kansas focused on making organic semiconductors work better. It could be a promising alternative to silicon-based panels, the material normally used to produce solar cells seen everywhere from roofs to calculators. Unfortunately, electrons inside the organic materials don’t tend to move as well, with many electrons paired with missing counterparts called “holes.”

The two research groups at the university looked at molybdenum disulfide, a two-dimensional semiconductor, to see if that could solve the problem. They found an atomic layer of the material creates more “free” electrons that don’t stay bound to their missing pairs. That allows them to move through the material freely. This breakthrough is critical to making a solar panel work, which uses sunlight to bounce electrons free that can then be run into a circuit to generate electricity.

Chan’s team only focused on the physics side of the issue, and it will be up to other researchers to bring it to a more marketable state. Nonetheless, he’s positive about its long-term potential.

“The efficiency is starting to get close,” Chan says. Regular silicon-based cells have an efficiency yield of around 20 percent. For the organic materials, the most efficient can reach around 15 percent. That means they don’t generate quite as much energy as regular panels, but it’s not too far off.

The other issues left to solve include long-term stability, as the panels would be expected to last decades. But if it reaches a level where efficiency is high, stability is assured, and the product is marketable, it could lead to lower prices.

As the world tries to limit emissions and reach net zero carbon emissions, every breakthrough could help.

Read the abstract for the team’s paper below:

Monolayer transition-metal dichalcogenide crystals (TMDC) can be combined with other functional materials, such as organic molecules, to form a wide range of heterostructures with tailorable properties. Although a number of works have shown that ultrafast charge transfer (CT) can occur at organic/TMDC interfaces, conditions that would facilitate the separation of interfacial CT excitons into free carriers remain unclear. Here, time-resolved and steady-state photoemission spectroscopy are used to study the potential energy landscape, charge transfer, and exciton dynamics at the zinc phthalocyanine (ZnPc)/monolayer (ML) MoS2 and ZnPc/bulk MoS2 interfaces. Surprisingly, although both interfaces have a type-II band alignment and exhibit sub-100 fs CT, the CT excitons formed at the two interfaces show drastically different evolution dynamics. The ZnPc/ML-MoS2 behaves like typical donor–acceptor interfaces in which CT excitons dissociate into electron–hole pairs. On the contrary, back electron transfer occur at ZnPc/bulk-MoS2, which results in the formation of triplet excitons in ZnPc. The difference can be explained by the different amount of band bending found in the ZnPc film deposited on ML-MoS2 and bulk-MoS2. Our work illustrates that the potential energy landscape near the interface plays an important role in the charge separation behavior. Therefore, considering the energy level alignment at the interface alone is not enough for predicting whether free charges can be generated effectively from an interface.