Light wavefront shaping to boost solar yield

April 25, 2016 // By PAUL BUCKLEY
Experimental setup for measuring light falling on and moving through an opaque layer, using fluorescent microscopy to monitor the results.
Researchers at University of Twente have turned light propagating in a layer of scattering nanoparticles, which typically is associated with a principle of diffusion and creates a falling diffusion curve, into a rising diffusion curve, by manipulating the incident light.

By transforming the diffusion curve the result is more light energy being held inside an opaque layer which could lead to better yields for solar cells or LEDs.

The research results are published in New Journal of Physics.

Even in a medium characterized by randomness, like a collection of non-organized particles that all scatter light, the net spreading of light is uniform. This is typical for diffusion.

The randomness in the UT Complex Photonics Group's experiments exists in a layer of white paint. Light that is falling on the collection of zinc oxide particles the paint is made of, will be scattered by the particles and will start interfering with light, scattered from neighbouring particles. Nevertheless, it will spread out in a uniform way. Theoretically, the energy density will show a linear fall-off with penetration depth. The scientists of the Complex Photonics Group (MESA+ Institute for Nanotechnology) did not take this for granted and worked on a way to turn the falling curve into a rising one so as to enhance the energy level inside the layer. Following the fundamental diffusion curve, the energy density rises until half of the layer and then falls off.

Experimental setup for measuring light falling on and moving through an opaque layer, using fluorescent microscopy to monitor the results.

The scientists have not altered the layer only the light. The ‘wave front shaping’ technique used was developed earlier on, leaving the way open to program the light waves in such a way that they choose the best pathways and show a bright light spot at the backside of the layer. The technique is also suitable for active control of the diffusion process.