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The Australian National University

Nanostructures for solar cells

Nanotechnology is the science of the small. It involves using new scientific understanding and new fabrication techniques to achieve much greater control over the properties of materials and devices. Nanotechnology has the potential to allow solar cells to be more efficient and thinner, both of which would make solar cells cheaper. In this project we are focusing on nanophotonics, that is, using nanotechnology to improve the optical properties of solar cells.
nanostructure pyramide

A: pyramid structure to reduce reflection

electromagnetic field around nano-scale metal cylinder

B: electromagnetic field around nano-scale metal cylinder

Conventional solar cells are made from silicon wafers, which are around 300 microns (1/3 of a millimetre) thick. The top surface of these cells is covered with pyramids around 10 microns high. The pyramids reduce the reflection from the top surface and trap the light inside the solar cell (see figure A).
To reduce the cost of solar cells, thin film solar cells are being developed. These are only a few microns thick and have the potential to be much cheaper than conventional solar cells, because they use much less silicon. Pyramid textures can’t be applied to these cells, so new structures are needed. Unlike pyramid textures, which can be described with geometrical optics, we need wave optics to predict the behaviour of these new structures. In this project we are investigating how metal nanoparticles and nano-structured surfaces can be used to increase the amount of light absorbed in a solar cell, and hence increase the amount of electrical current generated. Figure B shows the intensity of the electromagnetic field around a nano-scale metal cylinder as it scatters light into a thin silicon solar cell. Because the metal particle is nanoscale and because of the high refractive index of the silicon, instead of reflecting the light the metal particle actually scatters the light into the silicon.
nanostructure metal particles

C: metal particles

nanostructure metal particles

D: metal particles

The metal particles are formed using a simple self-assembly process of evaporating a thin layer of metal and then annealing it at low temperature to form metal particles. Pictures C and D show the metal particles, only about 100nm across, taken with a scanning electron microscope.

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