Buddhist singing bowls inspire new tandem solar cell design

8 September, 2014

in Fresh Science, Media releases

FameLab (Square)

The shape of a centuries-old Buddhist singing bowl has inspired a Canberra scientist to re-think the way that solar cells are designed to maximize their efficiency.

Dr Niraj Lal, of the Australian National University,  found during his PhD at the University of Cambridge, that small nano-sized versions of Buddhist singing bowls resonate with light in the same way as they do with sound, and he’s applied this shape to solar cells to increase their ability to capture more light and convert it into electricity.

“Current standard solar panels lose a large amount of light-energy as it hits the surface, making the panels’ generation of electricity inefficient,” says Niraj. “But if the cells are singing bowl-shaped, then the light bounces around inside the cell for longer”.

Normally used in meditation, music, and relaxation, Buddhist singing bowls make a continuous harmonic ringing sound when the rim of the metal bowl is vibrated with a wooden or other utensil.

During his PhD, Niraj discovered that his ‘nanobowls’ manipulated light by creating a ‘plasmonic’ resonance, which quadrupled the laboratory solar cell’s efficiency compared to a similarly made flat solar cell.

Now, Niraj and his team aim to change all that by applying his singing-bowl discovery to tandem solar cells: a technology that has previously been limited to aerospace applications.

Niraj Lal with the Buddhist bowl which inspired his research into solar cells (credit: OK-White Lane)

In research which will be published in the November issue ofIEEE Journal of Photonics, Niraj and his collegues have shown that by layering two different types of solar panels on top of each other in tandem, the efficiency of flat rooftop solar panels can acheive 30 per cent—currently, laboratory silicon solar panels convert only 25 per cent of light into electricity, while commerical varieties convert closer to 20 per cent.

The tandem cell design works by absorbing a sunlight more effectively —each cell is made from a different material so that it can ‘see’ a different light wavelength.

“To a silicon solar cell, a rainbow just looks like a big bit of red in the sky—they don’t ‘see’ the blue, green or UV light—they convert all light to electricity as if it was red ,” says Niraj. “But when we put a second cell on top, which ‘sees’ the blue part of light, but allows the red to pass through to the ‘red-seeing’ cell below, we can reach a combined efficiency of more than 30 percent.”

Niraj and a team at ANU are now looking at ways to super-charge the tandem cell design by applying the Buddhist singing bowl shape to further increase efficiency.

“If we can make a solar cell that ‘sees’ more colours and  keeps the right light in the right layers, then we could increase efficiency even further,” says Niraj.

“Every extra percent in efficiency saves you thousands of dollars over the lifetime of the panel,” says Niraj. “Current roof-top solar panels have been steadily increasing in efficiency, which has been a big driver of the fourfold drop in the price for these panels over the last five years.”

More importantly, says Niraj, greater efficiency will allow solar technology to compete with fossil fuels and meet the challenges of climate change and access.

“Electricity is also one of the most enabling technologies we have ever seen, and linking people in rural areas around the world to electricity is one of the most powerful things we can do.”

Niraj was a 2014 national finalist of FameLab Australia. FameLab is a global science communication competition for early-career scientists. His work is supported by the Australian Research Council and ARENA – the Australian Renewable Energy Agency

Media Contacts:

Dr Niraj Lal, Australian National University, 0421 090 940, niraj.lal@anu.edu.au

Niall Byrne, Science in Public, 0417 131 977, niall@scienceinpublic.com.au

Toni Stevens, Science in Public, 0401 763 130, toni@scienceinpublic.com.au

Background

Normally used in meditation, music, and relaxation, Buddhist singing bowls make a continuous harmonic ringing sound when the rim of the metal bowl is vibrated with a wooden or other utensil.

In his initial PhD research at the University of Cambridge, Niraj took an organic solar cell the size of a five-cent piece and layered it with hundreds of millions of nano-sized singing bowls.

You can read more of Niraj’s PhD work at: http://www.dspace.cam.ac.uk/handle/1810/243864

Abstract – IEEE Journal of Photonics

Optics and Light Trapping for Tandem Solar Cells on Silicon

Therapid advancement of thin-film photovoltaic (PV) technology increases the real possibility of large-area Si-based tandems reaching 30% efficiency, although light in these devices must be managed carefully. We identify the optical requirements to reach high efficiencies. Strict conditions are placed on material parasitic absorption and transmission of contacts: Absorption of 20% of sub-bandgap light leads to the required top-cell efficiencies of 18% at a bandgap of 1.5 eV to break even and 23% to reach tandem efficiencies of 30%. Perovskite-silicon tandem cells present the first low-cost devices capable of improving standalone 25% efficiencies and we quantify the efficiency gains and reduced thickness afforded by wavelength-selective light trapping. An analytical formalism for Lambertian tandem light trapping is introduced, yielding stringent requirements for wavelength selectivity. Applying these principles to a perovskite-based top cell characterized by strong absorption and high luminescence efficiency we show that tandem efficiencies greater than 30% are possible with a bandgap of Eg = 1.55 eV and carrier diffusion lengths less than 100 nm. At an optimal top-cell bandgap of 1.7 eV, with diffusion lengths of current vapor-depositedCH3NH3 PbIxCl1−x perovskites, we show that tandem efficiencies beyond 35% are achievable with careful light management.

Available online at: http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6880306&sortType%3Dasc_p_Sequence%26filter%3DAND%28p_IS_Number%3A5986669%29

The work described above was funded by the Australian Research Council, and the Australia Renewable Energy Agency.

About FameLab

In 2014, the British Council and Fresh Science have joined forces to bring FameLab to Australia.

FameLab Australia will offer specialist science media training and, ultimately, the chance for early-career researchers to pitch their research at the FameLab International Grand Final in the UK at The Times Cheltenham Science Festival from 3 to 5 June 2014.

FameLab is an international communication competition for scientists, including engineers and mathematicians. Designed to inspire and motivate young researchers to actively engage with the public and with potential stakeholders, FameLab is all about finding the best new voices of science and engineering across the world.

Founded in 2005 by The Times Cheltenham Science Festival, FameLab, working in partnership with the British Council, has already seen more than 5,000 young scientists and engineers participate in over 23 different countries — from Hong Kong to South Africa, USA to Egypt.

Now, FameLab comes to Australia in a landmark collaboration with the British Council and Fresh Science — Australia’s very own science communication competition.

For more information about FameLab Australia, head to www.famelab.org.au

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