Perovskite laser raises expectations for higher solar cell efficiencies

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Researchers working with perovskite, a material showing great promise for photovoltaics, have demonstrated perovskite cells can produce cheap lasers.

The scientists from Professor Sir Richard Friend’s group at Cambridge’s Cavendish Laboratory, working with Professor Henry Snaith’s University of Oxford group, sandwiched a thin layer of the lead halide perovskite between two mirrors to produce an optically driven laser. The cells ‘showed very efficient luminescence’, with up to 70 per cent of absorbed light re-emitted.

The new findings, recently published online in the Journal of Physical Chemistry Letters, raise expectations for even higher solar cell efficiencies, say the Oxbridge team, as well as potential uses for this material in telecommunications and for light emitting devices.

Perovskite solar cells, the source of huge excitement in the research community, already lie just a fraction behind commercial silicon in terms of efficiency, having reached a remarkable 17 per cent efficiency after only two years of research.

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.

Essentially, if a material is good at converting light to electricity, then it will be good at converting electricity to light. 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 solar cell efficiency,’ said Michael Price, co-author from the group in Cambridge.

Snaith added: ‘This luminescent behaviour is an excellent test for solar cell performance – poorer luminescence (as in amorphous silicon solar cells) 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.