Buildings in the future could be covered from top to bottom in thin materials which harness solar energy to provide all their energy needs, if emerging technologies can fulfill their potential.
It is estimated that buildings account for about 72 percent of electricity consumption in the U.S., according to the Department of Energy. As a result, innovative renewable solutions for buildings could help to significantly reduce greenhouse gas emissions, by making us less reliant on the burning of fossil fuels to generate electricity.
In an attempt to address this issue, researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have developed a new organic photovoltaic material that efficiently captures light—and could one day be applied to the surfaces of buildings.
Photovoltaic cells convert light into electricity using semiconducting materials—solid substances that have an electrical conductivity value somewhere between metals and insulators. Traditional photovoltaic roof-mounted solar panels, which are usually made from slabs of silicon, are efficient but they’re relatively expensive and not very adaptable. However, in recent times, researchers have been developing new types of “organic” solar cells which are made with “organic molecules”—generally defined as any chemical compound that contains carbon.
The main advantage of these organic molecules is that they can be dissolved into inexpensive inks that could then be printed onto thin sheets of material and applied to building parts, such as windows, walls or roofs.
“Organic photovoltaic technology is considered as one of the key novel ‘green’ technologies to overcome using ‘artificial’ forms of energy such as fossil fuels and nuclear materials,” Nicola Gasparini, an author of the study from the KAUST Solar Center, told Newsweek.
“As opposed to most inorganic photovoltaics, such as silicon, organic devices can be printed from a solution on plastic substrates, allowing for extremely thin, lightweight and elastic products that can be manufactured over large areas with freedom of shape,” he said.
However, organic solar cells are currently not as efficient as silicon-based solar cells and typically degrade fairly quickly. Part of the challenge when trying to develop a high-performance organic photovoltaic material is finding organic molecules that work effectively at every stage of the sunlight-electricity conversion process.
When light hits an organic photovoltaic material, it knocks free negatively charged electrons, leaving behind positively charged “holes.” However, if the electrons and positively charged holes recombine, then the captured energy from the sunlight will be lost.
To prevent this from happening, organic solar cells incorporate a mixture of so-called “electron donor” and “electron acceptor” molecules to keep the positive and negative charges apart.
“When I started my postgraduate studies in 2015, there was a lot of hype about fullerene buckyball derivatives as acceptors,” Derya Baran, another author of the study at the Solar Center, said in a statement.
However, these “fullerenes” have several drawbacks, notably, relatively poor light absorption. As a result, Baran and her team have been investigating different types of molecules called “non-fullerene acceptors”.
“I believe these acceptors will shape the future of organic photovoltaics,” she said.
For a study published in the journal Nature Communications, Baran and her team assessed a non-fullerene acceptor molecule known as “EHIDTBR.”
They found that the molecule strongly absorbs visible light and would be stable enough for long-term use. They have now incorporated the molecule into a new type of organic photovoltaic cell that is easy to manufacture.
“In this work we have designed a novel combination of materials forming the photoactive layer of an organic solar cell,” Gasparini said. “For many years, fullerene derivatives were the common electron acceptors in organic photovoltaic technology. We replaced the fullerene derivatives with non-fullerene small molecule acceptors and we obtained higher power conversion efficiency together with superior light stability, compared to fullerene-based solar cells.”
The next step for the researchers is to scale up the technology.
“We have a spin-out company from KAUST Solar Center and through this company we want to make photovoltaic windows for electricity generation,” Baran said.
Artem Bakulin, an expert in the science of photovoltaic technology from Imperial College London, who was not involved in the latest research, thinks that the solar cell reported in the latest paper is intriguing.
“To make a good solar panel, the organic molecules used in the solar cells should satisfy certain criteria, like efficient conversion of light to electrons, output voltage, stability etc,” he told Newsweek. “While the efficiency of the reported device is not outstanding, the combination of solar cell parameters is quite unique. In fact, only one issue is imperfect—the so-called ‘fill factor’ that indicates how easy is to extract generated electricity from the solar cell. If researchers can solve this issue as well, it will lead to a truly remarkable device.”
Bakulin notes that a few companies are currently demonstrating potential products based on organic solar cells. These look promising but are still a few steps away from being competitive at the market.
“This particular work shows that many important parameters of organic solar cells can be as good or even better than those of currently used silicon panels,” he said. “This indicates that, indeed, organics can be practically used when a few other issues, like fill factor, are solved. I believe when we have a stable, high-performance material, it will be a relatively simple engineering task to develop a way of printing semi-transparent organic panels on top of windows or integrating them into fabric.”