Single crystal perovskites promise cheaper solar cells and LEDs
Led by Professor Ted Sargent of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto and Professor Osman Bakr of the King Abdullah University of Science and Technology (KAUST), the team used a combination of laser-based techniques to measure selected properties of the perovskite crystals.
By tracking down the rapid motion of electrons in the material, the researchers have been able to determine the diffusion length — how far electrons can travel without getting trapped by imperfections in the material — as well as mobility — how fast the electrons can move through the material.
“Our work identifies the bar for the ultimate solar energy-harvesting potential of perovskites,” suggested Riccardo Comin, a post-doctoral fellow with the Sargent Group. “With these materials it’s been a race to try to get record efficiencies, and our results indicate that progress is slated to continue without slowing down..”
In recent years, perovskite efficiency has soared to certified efficiencies of more than 20 per cent, which is approaching the present-day performance of commercial-grade silicon-based solar panels.
“In their efficiency, perovskites are closely approaching conventional materials that have already been commercialized,” says Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author on the paper. “They have the potential to offer further progress on reducing the cost of solar electricity in light of their convenient manufacturability from a liquid chemical precursor.”
The study has obvious implications for green energy, but may also enable innovations in lighting. A solar panel made of perovskite crystals acts as a slab of glass: light hits the crystal surface and gets absorbed, exciting electrons in the material. The electrons travel easily through the crystal to electrical contacts on its underside, where they are collected in the form of electric current. If you imagine the sequence in reverse — power the slab with electricity, inject electrons, and release energy as light. A more efficient electricity-to-light conversion means perovskites could open new frontiers for energy-efficient LEDs.
Parallel work in the Sargent Group is focusing on improving nano-engineered solar-absorbing particles called colloidal quantum dots.
“Perovskites are great visible-light harvesters, and quantum dots are great for infrared,” said Professor Sargent. “The materials are highly complementary in solar energy harvesting in view of the sun’s broad visible and infrared power spectrum.”
“In future, we will explore the opportunities for stacking together complementary absorbent materials,” explained Dr. Comin. “There are very promising prospects for combining perovskite work and quantum dot work for further boosting the efficiency.”
Reference: ‘Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals’ Science 30 January 2015: Vol. 347 no. 6221 pp. 519-522. DOI: 10.1126/science.aaa2725
Related articles and links:
www.kaust.edu.sa
www.utoronto.ca
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