Molecular insights lead to improvements in organic solar cells

Molecular-level insight into Y-series nonfullerene acceptors (Y-NFAs) could help enhance their outdoor stability, a research team in Saudi Arabia has concluded.


This discovery by a King Abdullah University of Science and Technology (KAUST)-led team is expected to lead to applications including building-integrated photovoltaic windows and net-zero greenhouses. The team’s findings are detailed in Joule.

Organic solar cells are lightweight, flexible, quasi-transparent and can be manufactured at large scale. Efforts to boost power conversion efficiencies have led researchers to introduce Y-NFAs in the active layer of these devices.

Y-NFAs have broad absorption spectra, tuneable energy levels and excellent charge transport properties, making them ideal components for organic photovoltaics, said Han Xu, a PhD student at KAUST.

The research team has produced devices with efficiencies of 19 per cent, but the relationship between their molecular structure and stability is unclear. Steady performance of Y-NFA-based solar cells under real-world operating conditions also remains elusive, hindering the commercialisation of these devices.

As well as efficiency, the team said stability is critical when evaluating solar cells as ambient moisture and oxygen, light exposure and heat all influence the lifetime of a device.

“Outdoor evaluation, compared to lab-scale stability assessments, is the closest way to assess the real-world performance of a solar cell,” said Xu.


Xu and colleagues evaluated the outdoor stability of various Y-NFA-based solar cells under extreme hot Saudi conditions to understand the structure–stability relationship of these devices and guide the design of small molecules that would yield high-performance devices with enhanced stability.

To prevent moisture and oxygen from diffusing into the devices and counteract their effects, they wrapped the devices in thermoplastic polyurethane and measured the performance using outdoor sunlight as a light source.

“Our tests revealed that organic solar cells operating outdoors presented minor performance changes at 65oC and the overall stability of the solar cells is connected to their photostability,” Xu said in a statement. “Improving the photostability of active layer materials is crucial for enhancing the outdoor lifetime of solar cells.”

According to KAUST, the researchers found a link between the molecular structure and outdoor stability of Y-NFAs. They discovered that fluorine-bearing functional end groups and long hydrocarbon side-chains within Y-NFA molecules enhanced outdoor stability and protected them against photodegradation.

The researchers are planning international collaborations to conduct outdoor stability testing on different devices in various environments. They are also working toward making market-ready devices.

“The fabrication of large-area devices is indispensable for commercialisation, which calls for the integration of multiple technologies,” said Xu.