A Silicon Ratchet to Produce Power from Below-Bandgap Photons

What is it about?

A theoretical study, proposing a design for a device capable of using low-energy photons to produce an electrical current, by using the ratchet principles. Regular solar-cells rely on exciting electrons across a bandgap. Any energy beyond the band-gap is lost, and photons with energy below the bandgap cannot be used. Here we present a study exploring a new type of photovoltaic device, which can use below-bandgap photons (far-IR, THz range) to produce a current. The work used semi-classical simulations of a slab of Si with an asymmetric strain gradient. The strain splits and shifts conduction band energy levels, and a periodic asymmetric strain gradient will result in a like potential. The simulated device can harness below-bandgap, unpolarized, incoherent light to produce a current. Though the calculated efficiency was low, this proof-of-principle is very promising, and future simulation and experimental work will improve the performance

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