Singapore team sheds light on tapping solar power

A 'wonder material' known as perovskite could help sunny Singapore tap more sunlight than it ever could before. Audrey Tan looks at ongoing research at the Nanyang Technological University on how this material could revolutionise the local solar industry.
Audrey Tan Straits Times 2 Jun 17;

Scientists are finding out that tandem solar cells, which combine conventional silicon with other material, may have improved efficiency over the conventional silicon cell.

Researchers at the Nanyang Technological University (NTU) and the Singapore-Berkeley Research Initiative for Sustainable Energy are looking into tandem cells made by layering perovskite - a man-made substance - over silicon. They have shown that such cells have efficiencies of over 20 per cent.

In comparison, most silicon solar cells have efficiencies of between 17 per cent and 18 per cent, although more expensive models have recorded efficiencies of up to 25 per cent, said Professor Subodh Mhaisalkar, executive director of NTU's Energy Research Institute.

The efficiency of a solar cell is the proportion of energy from the sun that it turns into electricity.

But Professor Subodh said tandem cells, if used in combination with conventional silicon cells, for example, could achieve efficiencies exceeding 25 per cent in a solar module, or solar panel, which is made up of many connected cells.

The NTU-made tandem cell works by layering translucent perovskite over opaque silicon. Each layer captures a different "type", or colour, of light.

Light is electromagnetic radiation, some of which can be seen and some of which is invisible to the human eye. Infrared and ultraviolet radiation, for example, cannot be seen. They lie at either end of the visible spectrum of light.

Silicon solar cells are able to convert near-infrared light into electricity. But they are less efficient for visible and ultraviolet light.

Perovskite, on the other hand, is better at converting visible and ultra-violet light into electricity.

"So when light enters through the perovskite cell, the visible part of the solar spectrum is absorbed.

"The near-infrared light is then transmitted to the silicon cell where it is absorbed," said NTU Assistant Professor Nripan Mathews, one of the scientists doing perovskite research.

Over at the Singapore-MIT Alliance for Research and Technology (Smart), scientists are working on gallium arsenide-silicon tandem cells, which have recorded efficiencies of up to 25 per cent.

Gallium arsenide tandem cells are more expensive to make than perovskite ones, but the former also have higher efficiencies and are more stable for use on rooftops, said Professor Armin Aberle, chief executive of the Solar Energy Research Institute of Singapore. The institute is working with both NTU and Smart on tandem cell research.

Prof Aberle said tandem cells could provide more solar power per rooftop, helping land-scarce Singapore harvest more solar energy than with standard silicon panels.

He added: "The question is when inexpensive high-efficiency tandem solar panels will be commercially available... This technology still needs a lot of research and development in the laboratory until it can be commercialised."

Flexible solar panels could cover every surface here: Researchers
Audrey Tan Straits Times 2 Jun 17;

Singapore receives plenty of sunlight, but less than 2 per cent of its power supply comes from the sun.

A team of scientists at the Nanyang Technological University (NTU) wants to increase this.

How? One way is to cover every available surface in Singapore with solar panels, from the roofs of bus stops, to sloping building facades, and perhaps even the billboards along Orchard Road.

Last week, the researchers showed The Straits Times a prototype of what a flexible solar panel could look like - a 30cm by 30cm plastic sheet with a material called perovskite printed on it.

Conventional silicon-made solar panels are brittle and inflexible. But it is a different story if they are made of this "wonder material", which the scientists believe could revolutionise the solar industry here.

Perovskite used in making solar cells are synthesised in laboratories from elements such as carbon, hydrogen, nitrogen, lead and iodine. Like silicon, perovskite can convert sunlight into electricity.

But while silicon exists mainly as a breakable solid, perovskite can be printed onto plastic sheets - making flexible solar panels a possibility.

Various liquid chemicals, including the perovskite, are mixed together. The solution is then poured into a screen printer, such as those used in the T-shirt printing business, and printed onto sheets of plastic or glass.

Professor Subodh Mhaisalkar, executive director of NTU's Energy Research Institute, said glass-printed perovskite solar panels could become commercially available within the next three years.

As perovskite is translucent, and its colour can also be adjusted through chemical processes, such solar panels could be integrated into building facades.

This is not possible with current silicon-made solar panels, which are opaque and would block out light.

Prof Subodh is confident that new solar cell technologies, such as perovskite solar cells, could help the Republic tap more sunlight than ever before.

Perovskite panels allow sunlight to be harvested in places where solar energy cannot be tapped with silicon panels, such as on building facades and windows.

These perovskite panels would also be cheaper to produce, costing about three times less than conventional silicon cells, he said.

This is because perovskite can be printed onto large sheets of glass or plastic using printers similar to those used in the T-shirt printing business - doing away with the need for expensive materials and equipment required for manufacturing silicon solar cells.

The team also discovered that other than absorbing energy for conversion into electricity, perovskite nanoparticles can also emit light.

This allows for the potential application where a perovskite screen could function as both a display screen and solar panel, said the scientists.

The NTU team is working with scientists from the Singapore-Berkeley Research Initiative for Sustainable Energy on the perovskite research.

It also received funding from the National Research Foundation's Competitive Research Programme, which disburses funding of up to $10 million.

The National Research Foundation said: "Through the collaboration, we hope to achieve research and development breakthroughs that drive competitiveness of photovoltaic, which can in turn spur greater (solar) adoption in Singapore.

"This is key to achieving longer-term energy sustainability and security for Singapore."

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