Solar cells five times more efficient

MIT Scientists have discovered a way to transform nearly 100% of captured solar energy into electricity

March 2015

MIT Scientists have discovered a way to transform nearly 100% of captured solar energy into electricity. IMA LAB

Today’s solar cells convert roughly 20% of solar energy into electricity.

Scientists from the Massachusetts Institute of Technology (MIT) have discovered a system for making solar cells that perform five times better than this, transforming practically all the captured solar energy into electricity.

Up until now, the material used (usually silicone) has not been able to convert all the photons captured into electric energy, only those with a certain degree of energy. That’s to say, only light of certain wavelengths is actually converted to electricity. On top of this, with current photovoltaic cells, the higher the temperature of the material rises, the less efficient it becomes, so altogether roughly 80% of the energy gathered is not turned into electricity.

In part this problem had already been tackled by MIT technicians, who created a new “thermophotovoltaic” technology, capable of converting not only visible solar light into electricity but also the sun’s heat, regardless of its wavelength.

Panels made using this technology are divided into two layers. The outer layer is based on a phenomenon called “thermic emission” involving materials capable of acting as “concentrators”, which emit energy on a single pre-established wavelength. A second layer of material, optimized in order to convert energy of that wavelength into electricity, completes the operation. The problem with these systems is that, in order to work efficiently, they need effective “energy concentrators”, involving mirrors which concentrate solar light in single points. And this is difficult to achieve with fixed panels, where the angle of the sunlight changes continually.

The new MIT team, guided by engineer Jeffrey Chou, has now suggested the possibility of creating a “two-dimensional crystal in photonic dielectric metal”. This type of crystal would be capable both of absorbing light from a wide range of different angles – thus avoiding the need to rotate the panels in order to capture the sunlight – but also  be able to remain efficient at temperatures up to 1,000 degrees Celsius. These particular crystals are constituted by nanocavities inserted in a photovoltaic material.

Over the next five years, this system could be developed to manufacture cells able to convert the Sun’s energy (light, but also heat) with a degree of efficiency far outstripping anything achievable today, edging towards a 100% conversion rate.