Deformed light trap could improve solar cell efficiency

UK researchers are hoping to create better solar cells by increasing the amount of light they can store before absorbing its energy.

The scientists from York and St Andrews universities have found a way to improve the way micro-structures, known as optical cavities, can effectively store light by bouncing it back and forth between two deformed mirrors rather than two smooth ones.

The team, led by colleagues from King Abdullah University of Science and Technology (KAUST), Saudi Arabia, say that if the technology were applied to solar panels it could lengthen the time the light was in contact with the cells and so increase the chance it would be absorbed to create electricity.

Optical cavities are typically used in lasers to amplify the light signal by bouncing it back and forth through a gain medium, producing a beam that oscillates at a certain resonance frequency.

‘A normal cavity only resonates for certain wavelengths,’ York researcher Prof Thomas Krauss told The Engineer. ‘The cavity has a certain size so that limits the amount of oscillations you can have.

‘Our cavity can do more oscillations because it doesn’t create a regular light path, it’s not a straight bouncing back and forth. By deforming the mirrors, you make the light path irregular and that basically gives you more options – you can have resonances at more frequencies.’

The researchers showed deformed cavities could store six times the energy that traditional ones could. They also found the effects also worked in spherical cavities – microscopic glass balls that can trap light in a similar way – if the spheres were squashed.

Deformed optical cavities (b) resonate light at more frequencies than traditional cavities (a).

Krauss added that the research could also be used as a way of altering the colour of laser light, or to store light for use in optical quantum computing, but that its most promising application was in improving solar cells.

‘Many people work on grating-based solar cells, structures that afford the light trapping [principle],’ he said. ‘This adds another degree of freedom, another dial you can turn in order to improve your efficiency.’

Project leader, KAUST’s Prof Andrea Fratalocchi, said the new optical cavities exploited the principles of chaos and disorder.

‘The majority of our systems try to avoid these effects, as we commonly assume that chaos diminishes the performance of existing devices,’ he said in a statement.

‘The focus of my research, conversely, is to show that disorder can be used as a building block for a novel, low-cost and scalable technology that outperforms current systems by orders of magnitude.’

The research is published in the journal Nature Photonics.