Perovskite-Based Solar Cells Gaining in Efficiency
GOLDEN, Colo., April 29, 2014 — Perovskites are showing promise as materials for a new generation of highly-efficient, low-cost solar cells.
A team from the US Energy Department’s National Renewable Energy Laboratory (NREL) is studying the perovskite (CH3NH3)PbI3 to determine its effectiveness and potential applications in conjunction with titanium dioxide film of varying thickness. A semiconducting cube-like mineral, (CH3NH3)PbI3 has the same crystal structure as the mineral perovskite discovered in Russia’s Ural Mountains nearly 200 years ago.
Researchers have also found it easy to fabricate the perovskite using liquids that could be printed on substrates or made from simple evaporation.
The band gap of perovskites can be adjusted by changing their compositions to access different parts of the sun's spectrum. Courtesy of the National Renewable Energy Laboratory.
“Perovskite shows promise to be a whole lot easier to make” compared to most other solar cells, said Joey Luther, a senior scientist with NREL who works with nanomaterials. “It doesn't require high-temperature processing. You can just dip glass into two chemicals and get the material to form on it.”
Perovskite device structures, which are most commonly mesostructured and planar, have the ability to diffuse photons for long distances through a cell when processed in a liquid solution. Perovskite cells have “a diffusion length 10 times longer than their absorption length," according to Daniel Friedman, senior scientist with NREL.
This provides potential for low-cost, high-efficiency devices and makes it less likely that electrons will recombine with their hole partners and be lost to useful electricity, said David Ginley, an NREL research fellow.
Evolving techniques have increased peroskites’ efficiency from 3.8 percent in 2009 to 16 percent today. The theoretical maximum efficiency of a perovskite-based solar cell is about 31 percent, and multijunction cells based on this material could attain even higher efficiencies.
“The goal shouldn't be to stop at 20 percent efficiency,” Luther said. “The goal should be to try to get to 28 percent or higher. In the lab, the best cells need to be almost perfect at small scale. Then the commercial people can stop at whatever efficiency is economical for them to deploy.”
Perovskite could be tuned to access different areas of the sun’s spectrum by introducing impurities. Such solar cells, developed by NREL in 1991, are used most commonly in outer space applications and have long come with a high price tag. The new perovskite-based cells could pave an affordable route for their creation and application, researchers said.
NREL’s perovskite research has been published in two journals — The Journal of Physical Chemistry Letters (doi: 10.1021/jz401527q and 10.1021/jz500003v), and Chemical Communications (doi: 10.1039/C3CC48522F).
For more information, visit: www.nrel.gov
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