Nanoscale Charge Localization Induced by Random Orientations
of Organic Molecules in Hybrid Perovskite CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>
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Abstract
Perovskite-based solar cells have
achieved high solar-energy conversion efficiencies and attracted wide
attentions nowadays. Despite the rapid progress in solar-cell devices,
many fundamental issues of the hybrid perovskites have not been fully
understood. Experimentally, it is well-known that in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> the organic molecules CH<sub>3</sub>NH<sub>3</sub> are randomly orientated at the room temperature, but
the impact of the random molecular orientation has not been investigated.
Because of the dipole moment of the organic molecule, the random orientation
creates a novel system with long-range potential fluctuations unlike
alloys or other conventional disordered systems. Using linear scaling
ab initio methods, we find that the charge densities of the conduction
band minimum and the valence band maximum are localized in nanoscales
due to the potential fluctuations. The charge localization causes
electron–hole separation and reduces carrier recombination
rates, which may contribute to the long carrier lifetime observed
in experiments