UV light treatment may improve smartphone cameras

Treating an ordinary photodetector with ultraviolet light can turn it into a high bandwidth device, scientists have found paving a low-cost way to broaden the frequency range that smartphone cameras can detect.
Photodetectors, which are used in a wide range of systems and devices, are typically only sensitive to light within a certain narrow bandwidth, which causes numerous problems to product developers.
"There is a lot of demand for photodetectors that are sensitive to a wide range of frequencies, but they are difficult to design," said Vadim Agafonov, at Moscow Institute of Physics and Technology.
"It's hard to find the right materials, because the substances that permit ultraviolet light tend to be nontransparent to infrared radiation, and vice versa. We found a way to 'broaden' the spectral response of photodetectors," said Agafonov.

The team studied polymer photodetectors based on the internal photoelectric effect, ie, the redistribution of electrons within a polymer under the influence of light, resulting in electrical conductivity.
Photodetectors based on organic materials have a number of advantages over their conventional inorganic counterparts, including their low cost, easier manufacturing, and physical flexibility.

It turned out that by interacting with the surfaces of certain elements of the device, UV radiation can alter its sensitivity.
The researchers conducted an experiment whereby a polymer-based photodetector incorporating zinc oxide (ZnO) nanoparticles was exposed to UV light for 30 seconds.
As a result of this, they achieved a high-performance photodetector with a much broader spectral response and a maximum external quantum efficiency (EQE) of 140,000 per cent, as compared to the 30 per cent measured before UV treatment.

The EQE of a photodetector is an important figure of merit defined as the ratio between the number of "dislodged" electrons and the number of incident photons.
To put that in perspective, whereas before irradiation 10 photons generated just three electrons, after UV treatment the same number of photons produced 14,000 photoelectrons.
"You can thus convert a polymer-based photodetector into a highly sensitive broadband device. The process itself is quick, cheap, and efficient, which is important for practical applications," said Agafonov.
The study was published in the journal Advanced Functional Materials.