Laser shows promise for solar cell efficiency

Solar cells based on perovskite not only excel at absorbing light but at emitting it too, turning them into low-cost lasers says an Oxbridge team. Their discovery raises expectations for even higher solar cell efficiencies. Perovskite – a lead halide – excels at absorbing and emitting light, according to researchers from Cambridge’s Cavendish Laboratory. Working with an Oxford team, they sandwiched a thin layer of the material between two mirrors to produce an optically driven laser which shows very efficient luminescence, with up to 70% of absorbed light re-emitted. “The first demonstration of lasing in these cheap solution-processed semiconductors opens up a range of applications,” said Dr Felix Deschler from Cavendish Laboratory. “Our findings demonstrate potential uses for this material in telecommunications and for light emitting devices.” The researchers point to a fundamental relationship between the generation of electrical charges following light absorption and the process of recombination of these charges emit light. Essentially, if a material is good at converting electricity to light, it will also be good at the reverse. “Theoretical calculations have shown that a high radiative recombination (luminescence) is an indication for little losses in a material, which allows it to reach high photo-conversion efficiencies,” Deschler told Laboratory News. “The way in which a material works depends on the type of device it is built in. A solar cell itself optimises charge extraction, so to fabricate a dual device is very challenging.” Perovskite shows good luminescence and performance, even when simply prepared using cheap, scalable solution processing. Upon light absorption, two charges – electron and hole – are formed very quickly, within one picosecond, but it can 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 conductors. “Our results demonstrate that in these solar cells charge carriers are formed on very short timescales and that they are very long-lived,” Deschler said. “This explains the observed high-efficiencies and indicates that even higher ones, close to the theoretical maximum can be reached.” “We were surprised to find such high luminescence efficiency in such easily prepared materials,” said Michael Price, from the Cambridge group. “This has great implications for improvements in solar cells efficiency.” The work has been published in Journal of Physical Chemistry Letters. High Photoluminescence Efficiency and Optically-Pumped Lasing in Solution-Processed Mixed Halide Perovskite Semiconductors