22 april 2016

'It's my dream': achievement of scientist's solar cell goal opens up potentially huge new markets

Peter Hannam, Environment Editor, The Sydney Morning Herald, April 22, 2016

The sci-fi vision of solar cells coating surfaces from buildings to vehicles has been brought closer to reality after scientists at the University of NSW achieved new levels of electricity generation using non-toxic and abundant materials.

A team led by Hao Xiaojing, a senior lecturer at the Australian Centre for Advanced Photovoltaics, has produced thin-film solar cells made of copper, zinc, tin and sulphur (CZTS) that are able to convert light to electricity at a rate of 7.6 per cent in one-square centimetre cells.

The efficiency, confirmed earlier this month by the US National Renewable Energy Laboratory, is the highest achieved for cells of that size using these materials.

"This is the first step on CZTS's road to beyond 20 per cent efficiency, and marks a milestone in its journey from the lab to commercial product," Dr Hao said of her three-year project.

Standard rooftop solar panels using silicon now have a 15 to 16 per cent efficiency, while the best lab results reach 25.6 per cent.
The CZTS coating can be just a third of a micron. Human hair is about 100 microns thick.

Importantly, the large-scale solar farms now being built typically reach 20 per cent efficiency but their cells use toxic materials such as cadmium or selenide, and also rare elements like tellurium and indium.

As a result, existing thin-film rivals can "never provide the scale that the solar industry demands", said Martin Green, Scientia Professor at the centre and a globally recognised leader in the field.

Solar and wind energy scaled new heights in 2015 with a record capacity of 56 gigawatts and 62 gigawatts, respectively, 25 per cent more than the combined total a year earlier, the United Nations Environment Programme said this week. Renewables, excluding large-scale hydro power, made up 54 per cent of all new capacity last year, exceeding fossil fuels and other conventional electricity sources for the first time.

With an active material of just 350 to 700 nanometres, the cells being developed by Dr Hao and her team could potentially be used to coat a range of surfaces. With a structure including a base, such as molybdenum, the thickness may merely about two microns or about one-fiftieth of human hair.

"You can put them on car bodies, on steel, on tiles, polymers, or even silicon," Dr Hao said, noting their potential to become so-called building-integrated photovoltaics.

For Dr Green, part of the appeal is CZTS cells could be added as a layer to existing silicon-cell technology, boosting the efficiency to 30 per cent or higher.

CZTS responds better to the blue end of the light spectrum, while silicon responds well to the infra-red end.

"It's my dream – finding materials not scarce or toxic that you can put on silicon," Dr Green said.

Dr Hao's research was supported by funds from the Australian Renewable Energy Agency "in the hundreds of thousands" of dollars, Dr Green said, adding that future funding remained in doubt after the government ended its ability to make grants.
The final modules of AGL's Nyngan Solar Plant in western New South Wales were installed in April 2015.

The final modules of AGL's Nyngan Solar Plant in western New South Wales were installed in April 2015. Photo: AGL

While the CZTS cells currently have the efficiency levels of silicon cells of a couple of decades ago, Dr Hao predicts a doubling of 15 per cent efficiency – considered to be the entrance level of commercial viability – within five years.

>>> Back to list