(ORDO NEWS) — Scientists have created a sensor that converts light into an electrical signal with an astonishing 200 percent efficiency, a seemingly impossible figure achieved thanks to the oddities of quantum physics.
This is the sensitivity of the device. known as a photodiode, the team responsible for its innovation says it could potentially be used in technology that monitors a person’s vital signs (including heartbeat or breathing rate) without having to insert anything or even attach it to the body.
The efficiency of a photodiode is usually measured by the number of available light particles that it can convert into electrical signals.
Here the scientists are talking about something closely related, but a little more specific: the output of photoelectrons, or the number of electrons generated by photons hitting a sensor.
The photoelectron output of a photodiode is determined by its quantum efficiency – the essential ability of a material to produce charge-carrying particles at a fundamental level, rather than the amount of electricity generated.
“It sounds incredible, but we don’t talk about it. We are talking about conventional energy efficiency here,” says chemical engineer René Janssen from the Eindhoven University of Technology in the Netherlands.
“In the world of photodiodes, quantum efficiency is important. Instead of total solar energy, it counts the number of photons that the diode converts into electrons.”
As a starting point, the team worked on a device that combined two types of solar panel elements: perovskite and organic.
By stacking cells in such a way that light transmitted by one layer is captured by another, the researchers achieved a quantum efficiency of 70 percent.
To increase this figure, an additional green light was introduced. The sensor has also been optimized to improve its ability to filter different types of light and not respond to light at all.
This resulted in the quantum efficiency of the photodiode exceeding 200 percent, although at this stage it is not clear exactly why this increase occurs.
The key may be how the photodiodes produce the current. Photons excite electrons in the photodiode material, causing them to migrate and creating a charge buildup.
The researchers suggest that green light can release electrons on one layer, which are only converted into current when photons collide with another layer.
“We think that the extra green light leads to the accumulation of electrons in the perovskite layer,” says chemical engineer Riccardo Olearo from the University of Eindhoven technologies.
“This acts as a reservoir of charges that is released when infrared photons are absorbed by the organic layer.”
“In other words, every infrared photon that passes through and turns into an electron gets company from a bonus electron, resulting in an efficiency of 200 percent or more.”
A more efficient photodiode is also a more sensitive photodiode that is better able to observe very small changes in light over long distances. This brings us back to measuring heart rate and breathing levels.
Using an ultra-thin photodiode that is a hundred times thinner than a sheet of newspaper, the researchers measured small changes in infrared light reflected from a finger from a distance of 130 centimeters (51.2 inches).
This has been shown to match blood pressure and heart rate, much like a smartwatch sensor does, but works across a desk.
Using a similar setup, the team measured the respiratory rate during light chest movements.
There is potential here for all kinds of monitoring and medical purposes if the technology can be successfully developed from the laboratory stage.
“We want to see if we can further improve the device, for example by making it faster. “, says Janssen. “We also want to see if we can clinically test the device.”
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