50x more stability: Organic solar cells’ efficiency gets 56% boost with liquid crystals

Scientists have achieved a breakthrough in organic solar cells (OSCs), bringing the technology closer to commercial viability.

Researchers from the University of Illinois Urbana-Champaign demonstrated that achiral liquid crystal pathways show a 20 percent efficiency improvement and a three-fold stability improvement compared to random aggregation assemblies.

When printed with a helical structure, that number increased to 56 percent higher efficiency and 50 times more stable while the process was also successful for manufacturing.

With properties like lightweight, transparency, and foldability, organic solar cells are a compelling technology that can turn any surface into a power generator. It can be a suitable alternative to traditional silicon solar.

Organic solar cells can transform the energy industry

Researchers claimed that future innovations like backpacks and tents outfitted with OSCs that generate power on demand in the field or windows that turn sunlight into electricity can transform the energy industry.

Despite having multiple advantages over silicon solar cells, OSCs have remained non-ideal for real-world use due to the drop in their stability and efficiency during manufacturing.

However, researchers revealed that their latest innovation overcomes such challenges.

OSC is comprised of several nanometer-thin layers of film

“To address this problem, the researchers – led by chemical and biomolecular engineering professor Ying Diao – zeroed in on the molecular assembly process during fabrication. An OSC is comprised of several nanometer-thin layers of film. By manipulating the processing conditions when printing the films, they can force the molecules to adopt different structures,” said Alec M. Damron, co-first author.

“The ink evaporates while we’re printing, so – depending on how fast we print and how slow the evaporation – we can lock the assembly into different stages,” Damron said.

Damron revealed that when they printed their films slowly, as opposed to quickly, the evaporation portion of the physics dominated, forcing the polymers to assemble into liquid crystals before a film formed.

Researchers revealed that the finding was important because the liquid crystal structures resulted in better OSC stability and efficiency when compared to cells fabricated using random aggregation pathways.

Further manipulation during the process resulted in liquid crystal assembly pathways that were either achiral or chiral. Both resulted in a clear improvement in the efficiency and stability of the OSC, but the chiral – or helical – structure yielded the best results.

“We discovered that chiral assembly of conjugated donor polymers improves the crystalline packing and phase separated structure of the film,” said Azzaya Khasbaatar, the other co-first author on the paper.

“Improving film crystallinity not only enhances efficiency by improving charge transport but also makes the films much more morphologically stable.”

The study revealed that the trend researchers saw in improved performance through the liquid crystal phase versus the random fiber aggregation is general and can be applied to various organic solar cell materials.

Damron revealed that since that relationship has been established, it is possible to start from that as a baseline and continue building up on the engineering side.

Before their work, Diao said that very little was known about what happens between the time you apply the ink to a substrate and when you print the device, calling it a “black box.”

“People mainly focus on the material side and then the device side, but the middle is neglected. And that’s something we basically shed light on. We’re lifting the curtain on the hidden process and, by doing so, we are providing pathways to creating better devices,” said Diao.