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Excitonics/Perovskite Seminar Tomorrow!
Origins of Delayed Recombination and Halide Segregation in Metal Halide Perovskites*
January 18, 2018 at 12 noon/13-3038
Kyle Frohna
University of Cambridge, UK, Visiting Researcher
[
http://www.rle.mit.edu/excitonics/wp-content/uploads/2018/01/frohna-200x300…]
The origin of the long carrier lifetimes in metal-halide perovskites observed at low
photoexcitation carrier densities is a hotly debated topic. To date, a variety of
mechanisms have been proposed explaining this behavior including: polaron formation,
long-lived trap states, as well as the direct-indirect nature of the bandgap, which has
been attributed to the Rashba effect. However, the Rashba effect requires the breaking of
the centrosymmetric I4/mcm space group, which is a subject of considerable disagreement in
the community. We have recently probed the space group of room temperature tetragonal
MAPbI3 using second harmonic generation rotational anisotropy (SHG-RA). In this seminar, I
will discuss a combination of the SHG-RA measurements, first principles density functional
theory calculations, and analytical van Roosbroeck-Shockley calculations to investigate
the implications the Rashba effect may have on the radiative lifetime of perovskites.
I will also discuss photo-induced halide segregation, a phenomenon that has been put
forward as a potential cause of the reduced performance of wide bandgap, mixed-halide
perovskites for tandem solar cells. Large voltage deficits have been observed in these
perovskites due to thermalisation of carriers into lower bandgap, iodide-rich regions. By
compositionally engineering these perovskites and monitoring their behavior using
steady-state photoluminescence and voltage measurements, a new strategy for mitigating
halide segregation will be shown.
Kyle Frohna is currently a visiting researcher working with Samuel D. Stranks in the
Cavendish Laboratory at the University of Cambridge. He recently completed his
undergraduate degree in Nanoscience and Materials Science at Trinity College, Dublin. He
has worked previously with Professor Marco Bernardi at the California Institute of
Technology on computing the transport properties of carriers in metal halide perovskites
and he completed his undergraduate thesis project with Professor Michael McGehee at
Stanford University on the fabrication of high efficiency perovskite-silicon tandems.
*This talk is part of the Perovskites Seminar Series organized by Juan-Pablo Correa-Baena
from MIT's PV Lab and sponsored by the Center for Excitonics. For more info contact
Juan-Pablo: jpcorrea@mit.edu<mailto:jpcorrea@mit.edu>
The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S.
Department Of Energy,
Office Of Science And Office Of Basic Energy Sciences
Catherine Bourgeois
Program Manager
Assistant to Director
Research Laboratory of Electronics
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