Solar – Higher Power

Silicon-based solar cells based on existing microtechnologies have a maximum efficiency of about 25% (in the laboratory) and about 14% from those that can be bought from stores. The low efficiency is down to two things: silicon absorbs light within a very defined spectrum to convert into electrical current (this is known as the bandgap, the rest of the light is either not absorbed or radiated as heat) and secondly, some of the absorbed energy is lost through poor conductivity within the solar cell. New nanomaterials and structuring solar cells at the nanoscale can help overcome both of these obstacles.

Semiconductors other than silicon can be used for solar cells (such as gallium, indium, and germanium). Each semiconductor (or mixed compound of semiconductors) has a different bandgap; so if combinations of these are applied one on top of the other in thinfilms (a few tens of nanometres thick) then each layer can absorb different parts of the spectrum of light, thus increasing the overall amount of energy absorbed. Known as multi-junction solar cells, these have achieved an efficiency of 35%. Another key aspect of these types of solar cell is that the crystal structure of each layer must be precisely matched to ensure efficient electrical transfer. Note that such semiconductors can be used “in reverse” to produce different colours of light in light emitting diodes (LEDs).

In the future Quantum Dots are predicted to provide the highest efficiency solar cells at around 85%. This is because Quantum Dots can be produced in different sizes and chemical composition to capture all available light.