Research into perovskites looks beyond materials usage for efficient solar cells
Scientists at the Energy Department's National Renewable Energy Laboratory (NREL) discovered a use for perovskites that runs counter to the intended usage of the hybrid organic-inorganic material.
Today, Nature Communications published the research, Large Polarization-Dependent Exciton Optical Stark Effect in Lead Iodide Perovskites. Authors of the paper are Ye Yang, Mengjin Yang, Kai Zhu, Justin Johnson, Joseph Berry, Jao van de Lagemaat, and Matthew Beard.
The discovery was made by accident, said Beard, and occurred while the researchers were investigating excitons in perovskites. The sample was illuminated with a short laser pulse whose wavelength was specifically tuned to avoid being absorbed by the sample. Instead, the exposure triggered a strong interaction of light with the perovskite, producing a shifted transition energy known as the optical Stark effect. The effect occurs in semiconductors, but typically can only be observed at extremely low temperatures in very high-quality, high-cost materials. NREL's scientists were able to observe the effect quite readily at room temperature in materials grown using solution processing.
The NREL researchers used the optical Stark effect to remove the degeneracy of the excitonic spin states within the perovskite sample. An electron can have either "up" or "down" spins, and electrons with opposite spins can occupy the same electronic state. Circularly polarized light can be used to only interact with one of the spin states, shifting its transition energy.
The optical Stark effect possesses promising applications, including the potential to be used as an ultrafast optical switch. In addition, the optical Stark effect can be used to control or address individual spin states, which is needed for spin-based quantum computing.
Additional research is needed. The researchers must demonstrate they can control the spin states and address whether the stability problems that have hampered the use of perovskites as solar cells also are a factor in this area.
Funds for the research came from the Energy Department's Office of Science.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.
Visit NREL online at www.nrel.gov