Discovery improves silicon solar efficiency

A team of UNSW Sydney scientists and engineers have found a way to push past one of the biggest limits in renewable technology.

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. 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.”

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. “It’s still an early step, but it’s the first demonstration that this can actually work in a realistic system.”

The discovery builds on more than a decade of fundamental research led by Professor Tim Schmidt, head of UNSW’s School of Chemistry. His team used magnetic fields to reveal a key part of the singlet fission pathway.

“Our previous study addressed the route of this process,” Schmidt said. “We used magnetic fields to manipulate the emitted light and reveal how singlet fission occurs. This hadn’t been done before.”

By understanding these underlying physics, the researchers were able to design better materials and layer structures to make the effect more efficient.

“Different colours of light carry different energies,” Schmidt said. “Blue light has more energy, but most of that gets lost as heat in a normal solar cell. “With singlet fission, that excess energy can be turned into usable electricity instead.”

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,” Tayebjee 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.

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.”

The Australian Renewable Energy Agency (ARENA) selected UNSW’s singlet fission project in 2023 for its Ultra Low Cost Solar program, which aims to deliver panels capable of more than 30% efficiency at less than 30 cents per watt by 2030.

Seven of the world’s largest solar companies are already watching the Omega Silicon team closely.

“We have industry partners waiting in the wings,” Carwithen said. “They’re ready to help commercialise this if we can show it works in the lab.”

He estimates a small-scale proof of concept could be ready within years — but admits science doesn’t always move in straight lines.

“There could be a big breakthrough next week and everything clicks,” he said. “But a more realistic timeline is five years.”

The experimental work was led by a multidisciplinary research team across multiple schools at UNSW, from chemistry (Dr Matthew Brett) to physics (Dr Alex Baldacchino) to photovoltaics (Drs Shona McNab, Jingnan Tong and Victor Zhang).

Image credit: iStock.com/undefined undefined