Linking energy loss to interfaces in organic solar cells could make them much more efficient

New analysis from North Carolina State College gives a deeper understanding of exactly what is going on in natural photo voltaic cells as gentle is transformed into electrical energy. Researchers have developed a brand new technique that visualizes interfaces the place daylight’s power is transformed to electrical fees, and so they have used the findings to develop a set of design guidelines that may enhance the effectivity of natural photo voltaic cells.

The analysis is published within the journal Matter.

Natural photo voltaic cells are made with carbon-based polymer supplies which have the potential to be low value, could be made out of earth-abundant supplies, and have some engaging options—equivalent to the truth that they are often made into semi-transparent or clear window functions. As well as, as skinny movie photo voltaic cells, they’ve the potential for light-weight and versatile photo voltaic functions amenable to roll-to-roll manufacturing—which might additionally make them straightforward to move and set up.

Nevertheless, organic solar cells haven’t been as environment friendly as silicon or perovskite photo voltaic applied sciences at changing gentle into electrical energy.

“Organic solar cells are made of a mixture of two materials,” says Aram Amassian, co-corresponding writer of a paper on the work and a college college scholar and professor of supplies science and engineering at North Carolina State College.

“Both materials harvest electrons from sunlight. However, one of the materials is a polymer that harvests electrons, but then has to interact with the second material in order to pass those electrons on. The polymer is called a donor material; the other substance, typically a small molecule, is called the acceptor materials.

“We knew that interfaces between donor and acceptor materials were responsible for a voltage loss—which is what currently limits the efficiency of organic solar cells. Our goal with this work was to gain a deeper understanding of what aspects of interfaces were responsible for the voltage loss so that we may improve them.”

To deal with this problem, the researchers developed a scanning-probe microscopy technique that allowed them to map not solely the topographic traits of the donor and acceptor mix, but additionally the power traits of the donor and acceptor supplies on the interfaces—such because the power gradient on the interface and the way disordered the donor and acceptor supplies are on the interface.

“This technique allowed us to determine how the degree of disorder of donor and acceptor molecules at the interface impacted the energy disorder,” says Daniel Dougherty, co-corresponding writer of the paper and a professor of physics at NC State. “Once we had mapped the energetics of all of these interfaces, we were able to compare those findings with the results of conventional methods that characterize the overall performance of an organic solar cell’s voltage loss.”

The crew wanted to beat one other key problem. Because the scanning-probe microscopy approach doesn’t instantly measure voltage loss, the crew couldn’t inform which interface was the primary offender.

“Blends of donor and acceptor materials give rise to many different types of interfaces at once and it is not clear which interfaces are responsible for voltage losses,” Amassian says.

“Our study revealed that the functional interface in modern high performance organic solar cells, such as PM6:Y6, is the sharp donor-acceptor interface,” Dougherty says. “The findings imply that this type of interface needs to be targeted to further reduce voltage losses.”

“Once we identified the functional interface associated with voltage loss, we conducted a series of investigations into which factors influenced voltage loss,” Amassian says.

“There has been a longstanding debate in the organic solar cell community between people who argued that voltage loss was driven by energy differential between constituent donor and acceptor materials and people who argued that voltage loss was driven by energetic disorder along interfaces. Our experiments show that both sides are correct—it’s a combination of both factors.”

The researchers efficiently demonstrated that it’s attainable to “fix” the power differential and tune the dysfunction at interfaces by altering the best way the donor and acceptor are blended throughout fabrication in such a means as to scale back the voltage loss as a lot as attainable.

“By controlling for one of the drivers of voltage loss, we were actually able to identify engineering solutions that will help the organic solar cell community minimize the other driver of voltage loss,” Amassian says.

“Essentially, voltage losses are reduced by selecting a pair of materials with minimal energy offsets. Practitioners can then further reduce energy losses by identifying a solvent and processing parameters that substantially reduce interfacial disorder. We’re optimistic the design rules we developed using this technique can be used to inform organic solar cell research and development moving forward.”