Solar goes perovskite
South Korea and Stanford University both have labs endorsing the use of metal halide perovskite layers on silicon and other solar cells. Numerous advances have now resulted in 50% efficiency increases on cheap silicon cells. Despite dissolving in water, it appears perovskite is likely to change the game for those of us (nearly all of us) who deal with the real world of panels on the roof and not the latest expensive invention for some space programme. The revolution inspired by the material is inspired by the double whammy of panchromatic light absorption and its ambipolar behaviour.
Our regular updates on renewables like solar energy last mentioned that cost was reducing, even with the University of Western Ontario’s use of tiny amounts of tesselated gold! or the now-outdated layer of various cadmium salts. The standard house-roof solar cell is likely to be adapted again to be much better, possibly losing an infra-red absorption that could be useful in the old-fashioned unmodified silicon cell. At the University of Oxford in 2012, it was discovered that, with perovskite, only visible light is absorbed with an efficiency of at least 10%, but this means the efficiency during normal daylight is vastly improved.
Last year, researchers at Abengoa Research in sun-rich Sevilla, Spain joined in the celebration of perovskite as a potential game-changer. .Since 2009, Stanford too have been increasing their perovskite efficiency from 4% to 20% absorption. With the necessary waterproofing (over a long lifetime) these coated silicon cells will prove a boon to the industry as it tries to displace fossil fuel electricity generation in regions where sunlight can be utilised. South Korea have pointed out that a current solar cell factory (there are quite a few in South Korea)needs very little modification to begin production of their cells with perovskite layers. Businesses with reduced capital expenditure from Europe to California suddenly began paying attention.
The new cells consist of a transparent plastic electrode with silver wires placed closely onto the perovskite, with the silicon cell beneath. A 5.6% rise in absorption may not sound much, but that is actually a 50% rise in efficiency. The remaining problem that these labs have is maintaining the perovskite in sunlight. Although 2017 will see the first commercial new perovskite solar panels, it is possible some factories will convert to this production before that. The adaptation of the new material for resistance to light degradation will have to be accomplished before then. They will use new thin-film architecture to avoid ultraviolet degradation in the older-style sensitised architectures.
Long term stability in a moist environment has been achieved by the plastic encapsulation by the transparent electrode. Perhaps the next step will avoid deterioration by UV light when a “mesoporous” titanium oxide layer has been sensitised with the perovskite. Apparently oxygen radicals on the oxide interfere with the material’s photogenerated holes (just don’t ask how! – unless you work in one of these many research institutes.)We have to understand how the perovskite performs with more pure research and use the applied research to build that embryonic solar industry even politicians can use for their own purposes!
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