The amount of energy able to be harvested from ‘invisible light’ and used in solar cells has been given a significant boost thanks to a new technology.
Scientists in Australia and the United States turned low energy light into heavy energy light able to be captured by solar cells using ‘oxygen’ as a key ingredient.
Researchers from the ARC Centre of Excellence in Exciton Science and UNSW Sydney found a way to ‘upconvert’ low, non-visible light to generate power.
The process will allow solar power arrays to generate more electricity from the same amount of sunlight as is currently used – making them more efficient.
Right now it is fairly inefficient and not really for commercial applications, according to Tim Schmidt, senior author on the paper, but they are working on improvements.
The Molecular Photonics Laboratories at UNSW Sydney where they are developing the ability to ‘convert’ low-energy light into higher-energy light
‘The energy from the sun is not just visible light,’ explained Schmidt, adding that spectrum is broad and includes infrared and ultraviolet light.
‘Most solar cells, charge-coupled device (CCD) cameras and photodiodes (a semiconductor that converts light into electrical current) are made from silicon, which cannot respond to light less energetic than the near infrared.
‘This means that some parts of the light spectrum are going unused by many of our current devices and technologies.’
To extend the range of sensitivity of these devices, and potentially increase the efficiency of solar cells, one strategy is to ‘upconvert light’.
Right now it is fairly inefficient and not really for commercial applications, according to Tim Schmidt, senior author on the paper, but they are working on improvements. Stock image
The process involves turning low energy light into more energetic, visible light which can excite the silicon in many solar panels.
‘One way of doing this is to capture multiple smaller energy photons of light and glue them together,’ Schmidt says.
This can be done by interacting the excitons – the bound states of electrons and electron holes that transport energy without net charge – in organic molecules.
Until now, this had never been achieved beyond the silicon band gap, which is the minimum energy that is required to excite an electron in silicon up to a state where it can participate in conduction.
However, Exciton Science researchers, based at UNSW Sydney, have resolved this challenge and it involved transforming oxygen to achieve their goal.
The researchers used semiconductor quantum dots, which are nanoscale man-made crystals, to absorb the low energy light, and molecular oxygen to transfer light to organic molecules.
Usually oxygen is detrimental to molecular excitons, but at such low energies its role changes and it can mediate energy transfer.
This allows the organic molecules to emit visible light, above the silicon band gap.
Contributing author Professor Jared Cole of RMIT University said in many instances without oxygen, lots of things work well and when you use oxygen it stops working.
‘It was the Achilles heel that ruined all our plans but now, not only have we found a way around it, suddenly it helps us.’
Elham Gholizadeh, Ph.D. student at UNSW Sydney and first author of the paper is working on the equipment that converts light
The efficiencies are still low, but the scientists have strategies to improve this in the near future and possibility make more efficient solar panels.
‘This is an early demonstration, and there’s quite a lot of development needed to make commercial solar cells, but this shows us it’s possible,’ said Schmidt.
Despite this, lead author Elham Gholizadeh, also of UNSW Sydney, is optimistic about the potential of the work to make a rapid positive impact on the research field.
‘As this is the first time we’ve been successful with this method, we will face some challenges,’ she says.
‘But I’m very hopeful and think that we can improve the efficiency quickly. I think it’s quite exciting for everyone. It’s a good method to use oxygen to transfer energy.
‘Violanthrone doesn’t have the perfect photoluminescence quantum yield so the next step will be to look for an even better molecule.’
The findings have been published in the journal Nature Photonics.
SOLAR POWER EXPLAINED: ENERGY IS CONVERTED FROM SUNLIGHT INTO ELECTRICITY
Solar panels convert energy from the sun into electrical power (stock image)
Solar power is the conversion of energy from sunlight into electricity.
Two methods for generating solar power exist.
Photovoltaics — the kind of solar panel you might see built into a calculator — are capable of directly converting light into electrical power.
In concentrated solar power systems, however, mirrors or lenses are first used to collect the sunlight that falls on a large area and focus it — creating heat that can be used to drive a steam turbine and generate electricity.
The productivity of solar panels is dependant on the sunlight they receive in a given location — a factor which is dependant on both latitude and climate.
Optimum locations for solar farms include the arid tropics and subtropics, with deserts lying at such low latitudes often being cloudless and getting around 10 hours of sunlight each day.
According to NASA, the eastern part of the Sahara — the Libyan Desert — is the sunniest place on the Earth.
Solar power accounted for 1.7 per cent of the world’s electricity production in 2017, and has been growing at a rate of 35 per cent each year.