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Aalto University News: The efficiency was so high that at first the researchers had a hard time believing the result. Now Aalto University spin-off company ElFys Inc. already supplies the record detectors for several industry sectors.
UV-light triggers electron multiplication in nanostructures. Figure: Wisa Förbom
Aalto University researchers have developed a black silicon photodetector that has reached above 130% efficiency. Thus, for the first time, a single photovoltaic device has exceeded the 100% external quantum efficiency limit at UV. This result opens new avenues for improving efficiencies beyond the famous Shockley-Queisser limit.
Aalto University researchers have developed a black silicon
photodetector that has reached above 130% efficiency. Thus, for the
first time, a single photovoltaic device has exceeded the 100% external
quantum efficiency limit at UV. This result opens new avenues for
improving efficiencies beyond the famous Shockley-Queisser limit.
'When we saw the results, we could hardly believe our eyes. Straight
away we wanted to verify the results by independent measurements', says
Prof. Hele Savin, head of the Electron Physics research group at Aalto University.
The independent measurements were carried out by the German National
Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB), which
is known to provide the most accurate and reliable measurement services
in Europe.
Head of the PTB Laboratory of Detector Radiometry, Dr Lutz Werner
comments, 'After seeing the results, I instantly realised that this is a
significant breakthrough - and at the same time, a much-welcomed step
forward for us metrologists dreaming of higher sensitivities'.
The secret behind the breakthrough: Unique nanostructures
The external quantum efficiency of a device is 100% when one incoming
photon generates one electron to the external circuit. 130% efficiency
means that one incoming photon generates approximately 1.3 electrons.
The researchers found out that the origin of the exceptionally high
external quantum efficiency lies in the charge-carrier multiplication
process inside silicon nanostructures that is triggered by high-energy
photons. The phenomenon has not been observed earlier in actual devices
since the presence of electrical and optical losses has reduced the
number of collected electrons.
'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', Prof. Savin explains.
In practice, the record efficiency means that the performance of any
device that is utilising light detection can be drastically improved.
Light detection is already used widely in our everyday life, for
example, in cars, mobile phones, smartwatches and medical devices.
'Our detectors are gaining a lot of attraction at the moment,
especially in biotechnology and industrial process monitoring', says Dr Mikko Juntunen, CEO of Aalto University spin-off company, Elfys Inc. They are already manufacturing the record detectors for commercial use.
The results leading to the record efficiency have been accepted for publication in Physical Review Letters with a title "Black-silicon ultraviolet photodiodes achieve external quantum efficiency above 130%".
More information:
Professor Hele Savin, Aalto University
ph. 050 541 0156
hele.savin@aalto.fi
CEO Mikko Juntunen, ElFys Oy
ph. 040 860 9663
mikko.juntunen@elfys.fi
