Electronics Weekly
Perovskites photo-voltaics are new and fast-improving which, according to Imperial College last year, rose in efficiency from less than four per cent in 2009 to over 20 per cent, on par with traditional solar cells.
Now a team of researchers from Universities of Cambridge and Oxford, and the FOM Institute in Amsterdam, has discovered that perovskite cells can re-cycle photons created when electron-hole pairs collide rather than loose the energy as longer wavelength photons or lattice phonons.
“It’s a massive demonstration of the quality of this material and opens the door to maximising the efficiency of solar cells,” said Cambridge researcher Felix Deschler. “The fabrication methods that would be required to exploit this phenomenon are not complicated, and that should boost the efficiency of this technology significantly beyond what we have been able to achieve until now.”
Reported in Science as ‘Photon recycling in lead iodide perovskite solar cells‘, the team focussed a laser on a 500nm thick lead-iodide perovskite structure and observed activity using infra-red spectroscopy.
Near-infra-red emission was seen adjacent to laser spot, and emissions further away (>50μm) were at the same wavelength as well as longer wavelengths (lower energies).
The surprise was seeing emission away from the spot at the same wavelength as near the spot, which had to be due to electron-hole pairs and photons repeatedly swapping energy.
The low-energy component enables charges to be transported over a long distance, but the high-energy component could not exist unless photons were being recycled,” said Luis Miguel Pazos Outón of Cambridge’s Cavendish Laboratory. “Recycling is a quality that materials like silicon simply don’t have. This effect concentrates a lot of charges within a very small volume. These are produced by a combination of incoming photons and those being made within the material itself, and that’s what enhances its energy efficiency.”
It is an interesting thought SEPAM, but fear not, people are already thinking about it – some talking about a recycling guarantee.
Quantities are low – it is a real thin-film technology – but the Pb is definitely not permanently locked-up even if it is sealed between two glass sheets as once they are broken it can wash out. (if I recall correctly, Pb-crystal glass does have exemptions because the Pb is safe from leaching).
If perovskite turns out to be as good as it is looking, something safe accommodation will have to be made to safely use it. BTW, the Pb-free version of perovskite appears to be trailing badly in efficiency.
A quick check suggests some lead halides are easily soluble in hot water. And solar panels do get rather hot.
Someone will have to eat the camel and grant an exception unless they can form a non-soluble halide.
Lead halide? Is this compatible with RoHS or will there be an exemption made?