Revolutionary solar cells double as lasers

Mar 28, 2014
This is an image of the laboratory in which the research was conducted. Credit: Winton Programme for the Physics of Sustainability

Commercial silicon-based solar cells - such as those seen on the roofs of houses across the country - operate at about 20% efficiency for converting the Sun's rays into electrical energy. It's taken over 20 years to achieve that rate of efficiency.

A relatively new type of solar cell based on a perovskite material - named for scientist Lev Perovski, who first discovered materials with this structure in the Ural Mountains in the 19th century - was recently pioneered by an Oxford research team led by Professor Henry Snaith.

Perovskite solar cells, the source of huge excitement in the research community, already lie just a fraction behind commercial silicon, having reached a remarkable 17% efficiency after a mere two years of research - transforming prospects for cheap large-area solar energy generation.

Now, researchers from Professor Sir Richard Friend's group at Cambridge's Cavendish Laboratory - working with Snaith's Oxford group - have demonstrated that perovskite cells excel not just at absorbing light but also at emitting it. The new findings, recently published online in the Journal of Physical Chemistry Letters, show that these 'wonder cells' can also produce cheap lasers.

By sandwiching a thin layer of the lead halide perovskite between two mirrors, the team produced an optically driven laser which proves these cells "show very efficient " - with up to 70% of absorbed light re-emitted.

The researchers point to the fundamental relationship, first established by Shockley and Queisser in 1961, between the generation of electrical charges following light absorption and the process of 'recombination' of these charges to emit light.

Essentially, if a material is good at converting light to electricity, then it will be good at converting electricity to light. The lasing properties in these materials raise expectations for even higher solar cell efficiencies, say the Oxbridge team, which - given that perovskite cells are about to overtake commercial cells in terms of efficiency after just two years of development - is a thrilling prospect.

"This first demonstration of lasing in these cheap solution-processed semiconductors opens up a range of new applications," said lead author Dr Felix Deschler of the Cavendish Laboratory. "Our findings demonstrate potential uses for this material in telecommunications and for light emitting devices."

Most commercial solar cell materials need expensive processing to achieve a very low level of impurities before they show good luminescence and performance. Surprisingly these new materials work well even when very simply prepared as thin films using cheap scalable solution processing.

The researchers found that upon light absorption in the perovskite two charges (electron and hole) are formed very quickly - within 1 picosecond - but then take anywhere up to a few microseconds to recombine. This is long enough for chemical defects to have ceased the light emission in most other semiconductors, such as silicon or gallium arsenide. "These long carrier lifetimes together with exceptionally high luminescence are unprecedented in such simply prepared inorganic semiconductors," said Dr Sam Stranks, co-author from the Oxford University team.

"We were surprised to find such high luminescence efficiency in such easily prepared materials. This has great implications for improvements in ," said Michael Price, co-author from the group in Cambridge.

Added Snaith: "This luminescent behaviour is an excellent test for solar cell performance – poorer luminescence (as in amorphous silicon ) reduces both the quantum efficiency (current collected) and also the cell voltage."

Scientists say that this new paper sets expectations for yet higher solar cell performance from this class of perovskite semiconductors. Solar cells are being scaled up for commercial deployment by the Oxford spin-out, Oxford PV Ltd. The efficient luminescence itself may lead to other exciting applications with much broader commercial prospects – a big challenge that the Oxford and Cambridge teams have identified is to construct an electrically driven laser.

Explore further: Scientists unravel the mechanism of the functioning of a new type of solar cell

More information: Paper: DOI: 10.1021/jz500528

add to favorites email to friend print save as pdf

Related Stories

Creating simpler, cheaper solar cells

Nov 13, 2013

Over the last four years, solar cells made from materials called perovskites have reached efficiencies that other technologies took decades to achieve, but until recently no-one quite knew why.

Scientists make breakthrough solar technology

Oct 21, 2013

In the near future, solar panels will not only be more efficient but also a lot cheaper and affordable for everyone, thanks to research by Nanyang Technological University (NTU) scientists.

Recommended for you

How the hummingbird achieves its aerobatic feats

15 hours ago

(Phys.org) —The sight of a tiny hummingbird hovering in front of a flower and then darting to another with lightning speed amazes and delights. But it also leaves watchers with a persistent question: How ...

New terahertz device could strengthen security

Nov 21, 2014

We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures ...

CERN makes public first data of LHC experiments

Nov 21, 2014

CERN today launched its Open Data Portal where data from real collision events, produced by experiments at the Large Hadron Collider (LHC) will for the first time be made openly available to all. It is expected ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.