New Discovery in Molecular Structure of Perovskite Breaks Efficiency Record

New Discovery in Molecular Structure of Perovskite Breaks Efficiency Record

Northwestern researchers have uncovered a way to limit perovskite’s rapid degradation, which could enhance the material’s potential as a more efficient and cost-effective solar solution.
As perovskite solar cells continue to gain traction in the industry, a team of researchers at Northwestern University has found yet another combination of cells that can maintain and retain energy at an even greater capacity.  

Led by Ted Sargent, professor in the Department of Electrical and Computer Engineering and co-executive director of Northwestern’s Paula M. Trienens Institute for Sustainability and Energy, the team’s main focus is to unite chemistry, physics, and engineering in their labs to advance perovskite technology to the same standard as conventional silicon solar cells.  

Unlike conventional solar cells, which are created from silicon, perovskite is notoriously unstable. But it is also promising because it can be adapted to absorb different wavelengths, making them potentially more efficient and cost-effective. Cheng Liu, lead author of the most recent study and a postdoctoral student in the Sargent lab, explains that noise is the main disruptor. 

“Perovskite degrades very fast,” Liu said. “After searching the literature, we found that the issue isn’t coming from just one defect, but rather the interference of noise is affecting the overall transport of energy. So our strategy has to be flexible, more universal.”  

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Taking this more universal approach, Liu began experimenting with different materials and molecular combinations. But with every iteration comes a new set of outcomes, most of which are negative.  

“When you combine the molecules, you can get a very negative effect,” he said. “To avoid the negative effects and guide a positive impact, we need to understand what is happening inside of the structure.” 

When they inspected the perovskite layers, they found that the molecules had a tendency to “recombine” with defects in the existing layers, rather than transporting from one layer of the cell to the next, causing it to degrade. This desire to repair itself isn’t necessarily a bad thing though, it just means they needed to find a combination of molecules that would work to repair surface defects and prevent electrons from recombining with them. 

Liu and his team discovered that sulfur molecules would do just that. By replacing carbon groups, the sulfer-modified methylthio molecule covers the defects and suppresses recombination. A second diammonium molecule then repels minority carriers to further reduce recombination—meaning the overall structure becomes more stable and efficient.  

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Utilizing the stringent QSS (Quasi-Steady-State) protocol, the team was able to achieve a National Renewable Energy Lab-certified efficiency of 25.1 percent, breaking the previous record of 24.09 percent. 

Liu explains that this is merely the latest development in a very complex challenge. He believes there are many more defects to address, and it will take further discovery and technological advancements to continue to make solar cells that are even more efficient. Machine learning will be a critical aspect of the team’s work, explained Liu. By allowing them to test their theories at an accelerated rate, the team will be able to get to their results faster. 

“We are introducing some emerging technologies to help in our initial exploration,” he said. “As the structure becomes more complex, we need to understand the role of each material and how we can combine them.” 

And, of course, chemistry can only take the industry so far. The burden is also on engineers to implement this next generation of molecular structures into a design that will further improve solar technology and make harnessing the power of the sun an even more viable option for society’s evolving energy needs. 

Cassandra Kelly is a technology writer in Columbus, Ohio.

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