With the addition of sensors and enhanced communication tools, it has become more challenging to provide a light and portable power source. Army-funded research shows a new method of converting heat energy into electrical energy, which can provide compact and efficient electricity.

Hot objects radiate light into the surrounding environment in the form of photons. The emitted photons can be captured by photovoltaic cells and converted into useful electrical energy. This energy conversion method is called Far Field Thermal Photovoltaics, or FF-TPV, and has been developed for many years; however, its low power density requires a high operating temperature of the transmitter.

Can generate electricity as long as the temperature is high? How to make it easy for the power supply

This research conducted at the University of Michigan and published in Nature Communications demonstrates a new method in which the spacing between the emitter and the photovoltaic cell is reduced to nanometers, thereby achieving a greater power output than FF-TPV. Transmitter temperature.

This method of capturing the energy trapped in the near field of the transmitter is called Near Field Thermal Photovoltaics or NF-TPV. It uses a customized photovoltaic cell and transmitter design, which is very suitable for near field working conditions.

According to reports, the power density of this technology is almost an order of magnitude higher than the best reported near-field TPV system, while the work efficiency is also increased by six times, paving the way for future near-field TPV applications. Dr. Edgar Meyhofer, Professor of Mechanical Engineering, University of Michigan.

Dr. Mike Waits said: "The Army uses a lot of electricity during deployment and battlefield operations, and it must be carried by soldiers or weight-constrained systems." "If successful, the near-field TPV can be used as a more compact and more efficient power source in the future because of these The equipment can work at a lower operating temperature than traditional TPV."

The efficiency of a TPV device is characterized by how much of the total energy transfer between the emitter and the photovoltaic cell is used to excite the electron-hole pairs in the photovoltaic cell. Although increasing the temperature of the emitter will increase the number of photons above the battery band gap, it is necessary to minimize the number of sub-band gap photons that can heat the photovoltaic cell.

"This is achieved by manufacturing thin-film TPV cells with an ultra-flat surface and a metal back reflector," said Dr. Stephen Forrest, professor of electrical and computer engineering at the University of Michigan. "The photons above the battery band gap are effectively absorbed by the micron-thick semiconductor, while the photons below the band gap are reflected back to the silicon emitter and recycled."

The team grows thin-film indium gallium arsenide photovoltaic cells on a thick semiconductor substrate, and then strips the very thin semiconductor active area of the cell and transfers it to a silicon substrate. All these innovations in equipment design and experimental methods have led to a new type of near-field TPV system. "The team achieved a record power output of ~5 kW/m2, which is an order of magnitude larger than the system previously reported in the literature," said Dr. Pramod Reddy, a professor of mechanical engineering at the University of Michigan.

Can generate electricity as long as the temperature is high? How to make it easy for the power supply

The researchers also performed state-of-the-art theoretical calculations to estimate the performance of photovoltaic cells at each temperature and gap size, and showed good agreement between experiments and calculation predictions. "The current demonstration is in line with the theoretical predictions of nano-scale radiant heat transfer and directly demonstrates the potential of developing future near-field TPV devices for the Army's applications in power and energy, communications and sensors," said Dr. Pani Varanasi, project manager, DEVCOM ARL Funded this work.