Research just published in Science Advances (I link it to you here) shows an incredible leap forward in the field of sensor technology. Big enough to be perplexing. In fact, the document presents a light sensor, a photodiode, capable of converting light into an electrical signal with an incredible 200% efficiency.
Yes, you understood correctly: the device, based on quantum physics, would produce more energy than it receives. Don't turn up your nose, I've already done it: and yet, the study is there.
And it could one day lead to health monitoring systems that don't need power, or who knows what else: but let's proceed step by step.
How a photodiode works
When talking about photodiodes, efficiency refers to number of light particles that can be converted into electrical signals. But there is a more specific aspect that scientists take into consideration: the yield of photoelectrons. In summary, the number of electrons generated by photons hitting the light sensor.
This type of yield is determined by the so-called quantum efficiency, i.e. the ability of a material to produce charge-carrying particles at a fundamental level. “What matters in the world of photodiodes is quantum efficiency,” he confirms Rene Janssen, chemical engineer at the University of Eindhoven. “Instead of the total amount of solar energy, what counts is the number of photons that the diode converts into electrons.” It is precisely this quantum efficiency that determines the yield of the photoelectrons, and therefore the effectiveness of the photodiode.
A record-breaking light sensor
The research team began the study by assembling a device that combines two types of solar cells: perovskite cells and organic cells. The result was an initial, surprising quantum efficiency of 70%: the already very encouraging starting point prompted the researchers to go further, introducing an additional green light to try to further improve the device's performance.
And it seems they succeeded: in fact, the device exceeded all expectations. The quantum efficiency of the photodiode was increased to 200%, and while it is not yet entirely clear why this increase occurred, the researchers have some hypotheses.
When photons strike the photodiode material, the electrons are excited and migrate, creating a buildup of charge that can be converted into electric current.
“We hypothesize that introducing green light could release electrons onto the perovskite layer,” says the chemical engineer Riccardo Ollearo, of the Eindhoven University of Technology, among the authors of the research. “These electrons are then converted into current only when the photons hit a different layer.”
In other words, every time an infrared photon is converted into an electron, it would receive the “company” of a “bonus” electron, and this would explain the incredible 200% (and potentially higher) efficiency.
“Impossible” light sensor: why it can be really important
There are still many questions to be answered and research continues, but it can lead to exciting developments for the future of clean energy in the medium term.
In the immediate future, the positive effects of this technology could be those in the diagnostic field. Such an efficient light sensor could detect even the slightest changes in light at greater distances, making it particularly useful for measuring heart rate and blood pressure.
The research team used this super-thin photodiode (one hundred times thinner than a sheet of newspaper) to measure changes in infrared light reflected from a finger from a distance of more than one meter. From there, you can measure quite a few things.
In the future
Such a technology can allow a person to know his vital status remotely, without wearing devices.
Parameters such as blood pressure, heart rate and respiratory rate can be observed without touching anything. Not even with a smartwatch. It can be done simply by being within range of a device based on a light sensor like this one.
It is indeed the case to say that "everything is illuminated".
