Engineering ultrafast exciton dynamics to boost organic photovoltaic performance

A team of researchers led by Professor Philip C.Y. Chow from the Department of Mechanical Engineering at the University of Hong Kong (HKU) has revealed how the structure of organic photovoltaic (OPV) materials affects their performance, providing critical insights for future OPV material development.

The discovery has been published in Energy & Environmental Science in an article titled "Engineering ultrafast exciton dynamics to boost organic photovoltaic performance."

OPV is a promising emerging solar technology that could be used to power devices in a variety of innovative ways. Unlike traditional solar panels, which are made from rigid inorganic materials, OPV is made from organic (carbon-based) materials, giving them unique benefits. OPV is lightweight, flexible, affordable, and non-toxic, making it ideal for use in city buildings and in wearable devices.

While OPV is not yet as efficient as traditional solar panels, it has shown great potential. Over the past five years, its efficiency in converting solar energy into electricity has improved significantly, from about 10% to more than 20%. This progress is largely attributed to the development of a series of new materials known as Y-type acceptors. However, the lack of full understanding by scientists regarding the workings of these molecules has impeded further advancements.

Discovery by the research team

Utilizing advanced tools, Professor Chow's research team has revealed how the structure of Y-type acceptors impacts their performance in OPV devices.

When sunlight hits an OPV material, it generates excitons (electron-hole pairs bound by Coulombic force). In Y-type acceptors, excitons transition from less organized (disordered) regions of the material to more organized (ordered) regions. The team has found a way to track this rapid movement, which occurs incredibly fast within picoseconds, or trillionths of a second.

The researchers also found that OPV materials with molecules that are neatly and uniformly packed enable excitons to move more quickly from disordered to ordered regions. The enhanced movement of excitons in Y-type acceptors is strongly linked to the improved solar conversion performance of the corresponding OPV devices.

Interestingly, the researchers discovered that Y-type acceptors perform optimally when the molecules are neither overly tightly packed nor too loosely packed. This "just right" (optimal) level of organization results in a more uniform material, facilitating more efficient movement of excitons and enhancing the overall performance of OPV devices.

This research is significant because it provides scientists with a clearer understanding of how to design better materials for OPV. By grasping the connection between a material's structure, its response to sunlight, and its performance, researchers can develop more efficient, reliable, and affordable solar technologies.

With further development, OPV has the potential to supplement traditional solar panels, offering a sustainable energy solution for urban cities, wearable technologies, and more. In essence, the findings bring us closer to creating flexible, affordable, and high-performance solar devices that can help power a greener future.

Provided by The University of Hong Kong