Scientists have found a new way to make organic solar cells much more efficient by turning what was once considered wasted energy into useful electricity.
The breakthrough could help make lightweight, flexible solar panels more powerful and support the development of cleaner energy technologies.
A research team from City University of Hong Kong (CityUHK) has discovered that tiny energy particles called spin-triplet excitons do not always have to be lost as heat.
Instead, they can be recycled and converted into electricity.
Using this new method, the researchers built an organic solar cell with an impressive power conversion efficiency of 20.5%.
Organic solar cells, also known as organic photovoltaics (OPVs), are different from traditional silicon solar panels.
They are made from carbon-based materials, making them lightweight, flexible, and potentially cheaper to manufacture.
Because they can be printed onto thin surfaces, they could be used in wearable electronics, windows, curved buildings, and other places where standard solar panels are difficult to install.
One of the biggest challenges for organic solar cells has been energy loss. When sunlight hits the material, it creates tiny packets of energy called excitons. These excitons normally separate into positive and negative charges that create electricity.
However, some become low-energy spin-triplet excitons, which researchers have long believed simply lose their energy as heat. For more than ten years, these triplet excitons were seen as a dead end.
The CityUHK team discovered that this belief is not always correct. Led by Professor Alex Jen Kwan-yue, the researchers studied a newly developed material called FTh-4F.
They found that electrical charges in this material lasted longer than the triplet excitons themselves. This surprising result suggested that the triplet excitons could break apart again and become free electrical charges instead of disappearing as heat.
To test the idea, the researchers created more triplet excitons and observed what happened. They confirmed that these excitons could indeed be converted back into useful charge carriers that could be collected as electricity. By carefully changing the material’s molecular structure, they made this recycling process happen more easily.
The team then added FTh-4F as a third component in an organic solar cell. This allowed the device to recycle triplet excitons that would normally be wasted, increasing its efficiency to 20.5%.
The researchers say they have already improved the technology even further in their laboratory, with newer organic solar cells reaching efficiencies above 21%. Although these results have not yet become commercial products, they show that the technology is moving forward quickly.
This discovery also builds on the team’s earlier work. In 2022, they developed a method to reduce the formation of triplet excitons in organic solar cells, helping them achieve an efficiency of more than 19%. Instead of simply preventing these excitons from forming, the new research shows that they can actually be recycled and put to good use.
The researchers believe this finding changes how scientists understand energy flow inside organic solar cells. It could lead to even more efficient solar technologies and support the development of clean, sustainable energy in the future.
