Articles
Researchers at the University of Cambridge have discovered a means of manipulating electrons in organic solar cells which could improve their performance to a level comparable with silicon-based cells.
Organic solar cells are a new class of cell that mimic the process of plant photosynthesis. They have interesting applications – but lack the efficiency to compete with the more costly commercial silicon cells.
At the moment, organic solar cells can achieve as much as 12% efficiency in turning light into electricity, compared with 20-25% for silicon-based cells. Organic solar cells use large, carbon-based molecules to harvest sunlight instead of the inorganic semi-conductors used in commercial silicon-based cells.
These organic cells can be very thin, light and highly flexible, as well as printed from inks similar to newspapers – allowing for much faster and cheaper production processes than current solar cells.
But consistency has been a major issue. Scientists have, until now, struggled to understand why some of the molecules worked unexpectedly well, while others performed indifferently. Now, researchers have discovered that manipulating the ‘spin’ of electrons in these solar cells dramatically improves their performance.
Researchers from Cambridge’s Cavendish Laboratory developed sensitive laser-based techniques to track the motion and interaction of electrons in the cells. To their surprise, the team found that the performance differences between materials could be attributed to the quantum property of ‘spin’.
‘Spin’ is a property of particles related to their angular momentum, with electrons coming in two flavours, ‘spin-up’ or ‘spin-down’. Electrons in solar cells can be lost through a process called recombination, where they lose their energy – or excitation state – and fall back into an empty state known as the ‘hole’. Researchers found that by arranging the electrons’ ‘spin’ in a specific way, they can block the energy collapse from recombination and increase current from the cell.
Dr Akshay Rao, a research fellow at the laboratory, said: “This discovery is very exciting, as we can now harness spin physics to improve solar cells. We should see new materials and solar cells that make use of this very soon.”
The Cambridge team believes this work could bring the large-scale deployment of solar cells closer to reality. In addition, design concepts resulting from the work could be applied to organic light-emitting diodes, allowing for more efficient displays in mobile phones and TVs.