In a major breakthrough, Aalto University researchers have developed a photovoltaic device with an external quantum efficiency of 132 per cent.
UV-light triggers electron multiplication in nanostructures. Figure: Wisa Förbom Photo: Aalto university
The researchers used nanostructured black silicon to achieve this efficiency of above 100 per cent. With a 100 per cent efficiency, a photovoltaic device can generate one electron every time a photon of light strikes the external surface, which then is harvested as electricity.
The researchers used black silicon as active material, and nanostructure shaped like cones and columns to absorb UV light.
The 132 per cent efficiency means that one has a 32-percent chance of generating two electrons from a single photon. This might sound fanciful as it is impossible to create energy from nothing.
The research team used black silicon as it can absorb photons and release electrons efficiently as it forms billions of small, nano-scale pits during the process. Additionally, the purpose behind using cone nanostructures is they reduce electron recombination at the surface of the material. All the above advances helped the photovoltaic device to achieve the external quantum efficiency of above 130% in the UV range without any amplification.
The researchers used photons to strike the active silicon to displace an electron out of its atoms. Under certain circumstances, one high-energy photon has the capacity to move two electrons, without violating any laws of physics.
This has immense possibilities for improving the design of solar cells and UV sensor industry. In generating solar energy, as in most such phenomenon, a lot of energy is wasted in the process. In the photovoltaic devices, the photons just reflect back or the electron generated falls back into the active material without activating the circuit.
“We can collect all multiplicated charge carriers without a need for separate external biasing as our nanostructured device is free of recombination and reflection losses,” explains Prof. Hele Savin, head of the Electron Physics research group at Aalto University.
The photovoltaic device with the 130 plus efficiency was tested and verified by the German National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB).
The new detectors are being manufactured for commercial use already, according to the research team. The 130 efficiency can improve the workings of any photodetector based devices like solar cells and light sensors.
“Our photodetectors are gaining a lot of attraction at the moment, especially in biotechnology and industrial process monitoring,” said Dr. Mikko Juntunen, CEO of Aalto University spin-off company, Elfys Inc.
The research has been published in the journal Physical Review Letters.