Spray-on solar cells

UNSW's Anita Ho-Baillie holds a perovskite solar cell.Anita Ho-Baillie’s team has set a new world efficiency record for trend-setting solar cells

They’re flexible, cheap to produce and simple to make – which is why perovskites are the hottest new material in solar cell design. And now, UNSW engineers have smashed the trendy new compound’s world efficiency record.

Speaking at the Asia-Pacific Solar Research Conference at the end of 2016, Anita Ho-Baillie, a Senior Research Fellow at the Australian Centre for Advanced Photovoltaics (ACAP), announced that her team at UNSW has achieved the highest efficiency rating with the largest perovskite solar cells to date.

The 12.1% efficiency rating was for a 16 cm2 perovskite solar cell, the largest single perovskite photovoltaic cell certified with the highest energy conversion efficiency. The record was independently confirmed by the international testing centre Newport Corp, in Bozeman, Montana. The new cell is at least 10 times bigger than the current certified high-efficiency perovskite solar cells on record.

“This is a very hot area of research, with many teams competing to advance photovoltaic design,” says Ho-Baillie, who is UNSW ‘born and bred’ having completed her Bachelor in Electrical Engineering through the UNSW Co-op scholarship program, and her PhD at UNSW.

“Perovskites came out of nowhere in 2009, with an efficiency rating of 3.8%, and have since grown in leaps and bounds. These results place UNSW amongst the best groups in the world producing state-of-the-art high performance perovskite solar cells. And I think we can get to 24% within a year or so.”

Perovskite is a structured compound, where a hybrid organic-inorganic lead or tin halide-based material acts as the light-harvesting active layer. It is the fastest-advancing solar technology to date, and attractive because the compound is cheap to produce and simple to manufacture, and can even be sprayed onto surfaces.

“The versatility of solution deposition of perovskite makes it possible to spray-coat, print or paint on solar cells,” says Ho-Baillie. “We hope one day to be able to spray it on any building fabric, device or even cars.”

Ho-Baillie, who came to Australia from Hong Kong when she was a teenager, said her inspiration to study photovoltaics came from a lecture Scientia Professor Stuart Wenham gave in one of her electronics courses. “He gave us a tutorial on using a solar panel to pump water. As soon as he removed the cover and you could see the workings, I remember feeling amazed that this technology provided power for free!” 

Starting with a research idea from her mentor Scientia Professor Martin Green, a team of zero and no knowledge about perovskites in 2013, Ho-Baillie says she started by reading every paper published on the topic. There were only 83. “By the time I finished reading everything, the number of papers had increased exponentially. Now there are thousands of publications in the area.” Today, she has a “wonderful” team of 12 PhD students and five staff and feels like they are onto something special. 

The versatility of solution deposition of perovskite makes it possible to spray-coat, print or paint on solar cells.

Anita Ho-Baillie, Senior Research Fellow, School of Photovoltaics and Renewable Energy Engineering

Most of the world’s commercial solar cells are made from a refined, highly purified silicon crystal. Just like the most efficient commercial silicon cells (known as PERC cells and invented at UNSW), they need to be baked above 800˚C in multiple high temperature steps. Perovskites, on the other hand, are made at low temperatures and are 200 times thinner than silicon cells.

Although perovskites hold much promise for cost-effective solar energy, they are prone to fluctuating temperatures and moisture, making them last only a few months without protection. Along with every other team in the world, Ho-Baillie’s is trying to extend its durability.

“Nevertheless, there are many existing applications where even disposable low-cost, high-efficiency solar cells could be attractive,” says Ho-Baillie. “Such as use in device charging and lighting in electricity-poor regions of the world.” 

The research is part of a collaboration backed by $3.6 million in funding through the Australian Renewable Energy Agency’s  (ARENA) ‘solar excellence’ initiative.

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