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Temperature Dependence of the Energy Levels of Methylammonium Lead Iodide Perovskite from First-Principles
journal contribution
posted on 2016-12-04, 00:00 authored by Wissam A. Saidi, Samuel Poncé, Bartomeu MonserratEnvironmental
effects and intrinsic energy-loss processes lead
to fluctuations in the operational temperature of solar cells, which
can profoundly influence their power conversion efficiency. Here we
determine from first-principles the effects of temperature on the
band gap and band edges of the hybrid pervoskite CH3NH3PbI3 by accounting for electron–phonon coupling
and thermal expansion. From 290 to 380 K, the computed band gap change
of 40 meV coincides with the experimental change of 30–40 meV.
The calculation of electron–phonon coupling in CH3NH3PbI3 is particularly intricate as the commonly
used Allen–Heine–Cardona theory overestimates the band
gap change with temperature, and excellent agreement with experiment
is only obtained when including high-order terms in the electron–phonon
interaction. We also find that spin–orbit coupling enhances
the electron–phonon coupling strength but that the inclusion
of nonlocal correlations using hybrid functionals has little effect.
We reach similar conclusions in the metal–halide perovskite
CsPbI3. Our results unambiguously confirm for the first
time the importance of high-order terms in the electron–phonon
coupling by direct comparison with experiment.