Sunny side up: new research boosts solar power

Trinity Fellow Dr Hannah Stern’s discovery of the physics of carbon molecules could pave the way for a new paint that significantly boosts the efficiency of solar cells – and impacts the photovoltaic industry.

Dr Stern, a Junior Research Fellow at Trinity, is part of the Optoelectronics Group at the Cavendish Laboratory, which investigates the physics of organic semiconductors. The group’s work is part of a broader Cambridge initiative to harness high-tech knowledge in physics to tackle global challenges such as climate change and renewable energy.

Under the direction of Professor Richard Friend, Honorary Fellow at Trinity, and Dr Akshay Rao, Early Career Research Fellow at the Engineering and Physical Sciences Research Council, Dr Stern and her colleagues probed how organic semiconductors convert energy to create multiple electrons that contribute to the electric charge in an inorganic solar cell.

Using a new spectroscopy method developed by postdoctoral researcher, Dr Alexandre Cheminal, the team discovered how singlet exciton fission converts high-energy particles from the sun into the lower energy particles that can be transferred to a silicon solar panel.

Dr Stern said: ‘We know this mechanism occurs in some organic semiconductors. Our research shows that it is possible to harness energy from the surroundings to produce electrons in a solar cell that have more energy that the absorbed photon used to create them. This class of materials is good for use in solar because they could be applied as a paint or coating to silicon cells that could boost efficiency by up to a third.’

While the cost of solar technology has dropped substantially over 10 years as new manufacturers enter the market, there has been no corresponding increase in efficiency. The research by Dr Stern and her colleagues could change all that.  She said:

At the moment solar is not as affordable as other forms of energy generation because it is not efficient enough. So even a small efficiency increase to existing solar technologies would make a huge difference to the industry.

Curiosity led Dr Stern to investigate endothermic singlet fission materials, which had been disregarded for industry application because they were thought to be inefficient. She said:  

We didn’t really understand the physics of endothermic molecules and we were curious. Endothermic means the photon to electron conversion requires absorption of energy from the surroundings to proceed, which usually means a reaction is ‘slow’ and inefficient, unlike exothermic reactions that are spontaneous and eventually lose the excess energy.  Our research probed how this endothermic reaction occurs and showed that an important intermediate state is formed, very quickly, which prevents the system from losing efficiency.

This new understanding of photophysics could mean huge steps forward in designing solar cells.

The team’s findings are published in Nature Chemistry. The research by the Optoelectronics Group at the Cavendish is backed by the UK Engineering and Physical Sciences Research Council, the Winton Programme for the Physics of Sustainability, and the Leverhulme Trust.