Dr Xiaojing Hao of UNSW’s Australian Centre for Advanced Photovoltaics holding the new CZTS solar cells. Credit: Quentin Jones/UNSW
‘Zero-energy’ buildings – which generate as much power as they consume – are now much closer after a team at UNSW, Australia achieved the world’s highest efficiency using flexible solar cells that are non-toxic and cheap to make. Until now, the promise of ‘zero-energy’ buildings been held back by 2 hurdles: the cost of the thin-film solar cells (used in façades, roofs and windows), and the fact they’re made from scarce, and highly toxic, materials.
NREL, USA’s National Renewable Energy Lab, confirmed this world leading 7.6% efficiency in a 1cm2 area CZTS cell this month. Unlike its thin-film competitors, CZTS cells are made from abundant materials: copper, zinc, tin and sulphur. And CZTS has none of the toxicity problems of its 2 thin-film rivals, known as CdTe (cadmium-telluride) and CIGS (copper-indium-gallium-selenide). Cd and Se are toxic at even tiny doses, while tellurium and indium are extremely rare. “This is the first step on CZTS’s road to beyond 20% efficiency, and marks a milestone in its journey from the lab to commercial product,” said Hao. “There is still a lot of work needed to catch up with CdTe and CIGS, in both efficiency and cell size, but we are well on the way.”
“In addition to its elements being more commonplace and environmentally benign, we’re interested in these higher bandgap CZTS cells for two reasons,” said Professor Martin Green, global pioneer of photovoltaic research stretching back 40 years. “They can be deposited directly onto materials as thin layers that are 50X thinner than a human hair, so there’s no need to manufacture silicon ‘wafer’ cells and interconnect them separately,” he added. “They also respond better than silicon to blue wavelengths of light, and can be stacked as a thin-film on top of silicon cells to ultimately improve the overall performance.”
By being able to deposit CZTS solar cells on various surfaces, Hao’s team believe this puts them firmly on the road to making thin-film photovoltaic cells that can be rigid or flexible, and durable and cheap enough to be widely integrated into buildings to generate electricity from the sunlight that strikes structures such as glazing, façades, roof tiles and windows. UNSW is collaborating with a number of large companies keen to develop applications well before it reaches 20% efficiency within the next few years.
The new high-efficiency, low-toxicity solar cells developed by UNSW’s Australian Centre for Advanced Photovoltaics.
Currently, thin-film photovoltaic cells like CdTe are used mainly in large solar power farms, as the cadmium toxicity makes them unsuitable for residential systems, while CIGS cells is more commonly used in Japan on rooftops.
Thin-film technologies such as CdTe and CIGS are also attractive because they are physically flexible, which increases the number of potential applications, such as curved surfaces, roofing membranes, or transparent and translucent structures like windows and skylights.
But their toxicity has made the construction industry – mindful of its history with asbestos – wary of using them. Scarcity of the elements also renders them unattractive, as price spikes are likely as demand rises. Despite this, the global market for so-called Building-Integrated Photovoltaics (BIPV) is already valued at US$1.6 billion.
Until now, most architects have used conventional solar panels made from crystalline silicon. While these are even cheaper than CZTS cells, they don’t offer the same flexibility for curved surfaces and other awkward geometries needed to easily integrate into building designs.
http://newsroom.unsw.edu.au/news/science-tech/unsw-takes-lead-race-non-toxic-thin-film-solar-cells
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