Semiconductor-free solar cell method created

Researchers at the University of Michigan have defied previously held known laws of physics to provide the basis for solar cells based on the magnetic properties of light, all without the use of semiconductors.

Scientists have up until now overlooked the possibilities of drawing energy from the magnetic field generated by light, but Stephen Rand’s team has found that the magnetic effects are 100 million time stronger than previously expected.

According to Rand the effect in question is taught in school to be an impossibility, and is described as a “very odd interaction”.

“That’s why it’s been overlooked for more than 100 years,” Rand says. “You could stare at the equations of motion all day and you will not see this possibility.”

But now an “optical battery” has been devised by using light at the right intensity to be passed through a material that does not conduct electricity in order to generate a magnetic effect.

According to the researchers this could potentially lead to a new kind of solar cell “without semiconductors and without absorption to produce charge separation”, with the intense magnetisation create by light being used as a “capacitive power source”.

This is done through a type of “optical rectification” according to the scientists, which essentially means pulling apart positive and negative charges in a material to set up a voltage, something which was previously only possible in certain crystalline materials.

However the team believes it has found a way to create optical rectification in the magnetic field of light, which can create significant amounts of energy when occurring in a row in a long fibre, allowing for a “huge voltage” that can be used as a power source.

In order to achieve high voltages, light needs to be focused to an intensity of 10 million watts per square, not immediately achievable with direct sunlight, but could work with materials that function at lower intensities.

“In our most recent paper, we show that incoherent light like sunlight is theoretically almost as effective in producing charge separation as laser light is,” Fisher said.

While this all sounds impressive the scientists are currently only working towards a level of efficiency seen in that of commercially available solar cells used at the moment, but they believe the lack of need for semiconductors could mean that, in terms of cost effectiveness, it could show a marked improvement.

As Fisher points out: to manufacture modern solar cells you have to do extensive semiconductor processing, while the light magnetism approach would need would be “lenses to focus the light and a fibre to guide it”.

“Glass works for both. It’s already made in bulk, and it doesn’t require as much processing. Transparent ceramics might be even better.”