Energy - Solar - About The Sector

Nanotechnology can be used to make solar cells more efficient and reduce their cost. Silicon is the main raw material for most photovoltaics (PV) and comprises 10-20% of their cost.

When photons impact n-type silicon (excess of conductive electrons), they cause atoms to lose electrons which then transfer to an adjacent electron deficient area of the silicon (p-type) creating a current and thereby generating electricity. The best commercial versions of solar cells are around 22% efficient at converting sunlight into electricity. By reducing the thickness of the silicon from the typical 200 micrometres to dimensions of nanometres, material costs are significantly reduced but to the detriment of the efficiency of the cell for the simple fact that there is less material, thus electrons, for the photons to interact with. To counteract the sacrifice in efficiency caused by thinning out the costly silicon, nanotechnology can be used to maximise the light entering the solar cell, through anti-reflective coatings; to minimise light escaping the solar cell, through nanostructured photonic waveguides; and to improve light absorption, through integrating plasmonic components.

In addition to crystalline silicon PV cells, nanotechnology is being used in the development of thin film photovoltaics (e.g. based on amorphous silicon, copper indium gallium selenide (CIGS) or cadmium telluride); in third generation PVs (using quantum dots, nanowires, organic and dye-sensitised solar cells); in concentrator PV cells using optical tracking and optical concentration; and in connecting PV cells to the grid.

Nanoscale roughening of the silicon surface can drastically reduce the light reflected from the surface. One example, inspired by the structure of moths’ eyes, used an ordered array of nano-sized posts fabricated on silicon using block copolymer patterning templates to decrease reflection. Most commercial strategies, however, employ multi-layered thin films and achieve similar efficiencies to the nano-pillar array.1

Once the light enters the active part of the solar cell, it should be prevented from escaping in order to maximise the probability of interaction with the electrons in the material.Resonant cavities and waveguides are used for this purpose along with plasmonic nanoparticles on the surface to scatter the light back into the active material. These plasmonic nanoparticles also enhance local electromagnetic fields and can improve the optical properties of the material when their resonance peak matches that of the incident light.

Another potential benefit of thinner solar-cells (developed through a combination of nanotechnology, material and fabrication advances) is that they would be more flexible and amenable to cheaper production techniques such as printing. They would also be easier to transport, possibly even rolled up, and to install, and can potentially be shaped to suit a variety of geometries.