UNSW scientists advance solar cell efficiency by splitting light

UNSW researchers have announced they are working towards a new generation of solar technology that could make sunlight work smarter — by turning one particle of light into two packets of energy.

Singlet fission is a process where a single particle of light — a photon — can be split into two packets of energy, effectively doubling the electrical output when applied to technologies harnessing the sun.

In a recent study, the UNSW team — known as ‘Omega Silicon’ — showed how this works on an organic material that could one day be mass-produced specifically for use with solar panels.

“A lot of the energy from light in a solar cell is wasted as heat — which itself is also a form of energy,” said Dr Ben Carwithen, a postdoctoral researcher at UNSW’s School of Chemistry. “We’re finding ways to take that wasted energy and turn it into more electricity instead.”

Most of today’s solar panels are made from silicon — a reliable and cheap technology. However, there are limits to silicon’s efficiency, with the best commercial cells currently converting about 27% of sunlight into electricity. The theoretical ceiling is about 29.4%.

Singlet fission offers a way past that barrier. When sunlight hits certain organic materials, one high-energy photon can produce two lower-energy excitations. So, two packets of usable energy are produced, instead of just one.

“Introducing singlet fission into a silicon solar panel will increase its efficiency,” said Professor Ned Ekins-Daukes, project lead and head of UNSW’s School of Photovoltaic & Renewable Energy Engineering. “It enables a molecular layer to supply additional current to the panel.”

Until now, the challenge was finding the right material. Earlier work by other teams had used a compound called tetracene, which performed well in the lab but then degraded too quickly in air and moisture to be practical. The UNSW team has now demonstrated that a compound called DPND, or dipyrrolonaphthyridinedione, can do the same job while remaining stable under real-world outdoor conditions.

“We’ve shown that you can interface silicon with this stable material, which undergoes singlet fission, and then injects extra electrical charge,” Carwithen said.

Supervising author UNSW Associate Professor Murad Tayebjee said this work is “a big step forward” for solar panel technology.

“It is the first demonstration of singlet fission on silicon using a relatively stable organic molecule based on industrial pigments,” he said.

A pigment is something that provides colour. Colours absorb light. Industrial pigments don’t degrade over time, such as those used in automotive paints, and the new technology works by adding an ultra-thin organic layer to the top of a conventional silicon cell.

“In principle, it’s just painting an extra layer on top of the existing architecture,” Carwithen said. “We need to find a way of making it work, but there’s no reason why it can’t.”

The theoretical limit for solar panels using singlet fission is around 45% efficiency — a huge leap forward from current technology.

“Pushing towards 30% would already be fantastic,” Carwithen said. “But there’s a higher ceiling we can hopefully reach.”

Image caption: The team uses this laser facility to study how light and energy behave — from visible to mid-infrared wavelengths, as well as along ultrafast time scales. Credit: Richard Freeman/UNSW Sydney