Source-linked AI summary
Charge carrier mobility in hybrid halide perovskites
Carlo Motta, Fedwa El Mellouhi, Stefano Sanvito
TL;DR
The paper addresses contrasting conclusions about perovskite efficiency and the expected role of charge transport, using rigorous density functional theory alongside semiclassical transport analysis. It reports transport-related effects and bandgap behavior while noting constraints from impurity scattering and device processing.
Problem
Contrasting conclusions about perovskite efficiencies and a knowledge gap motivate examining the expected role of charge transport.
Method
The analysis combines rigorous density functional theory with semiclassical transport theory and includes long-range van der Waals interactions.
Results
The reported effects include energy-gap renormalization, bandgap variations spanning much of the range within 1 ps, and differences emerging around 2 eV above the CBM.
Takeaways & Limitations
The analysis presents a first-principles examination of transport properties in organolead perovskites and compares structural configurations involving approximately 14° tilting.
Takeaways & Limitations
The stated upper bound may be reduced by impurity scattering, while experimental determination depends on device processing.
Abstract
from arXiv · showhide
The charge transport properties of hybrid halide perovskites are investigated with a combination of density functional theory including van der Waals interaction and the Boltzmann theory for diffusive transport in the relaxation time approximation. We find the mobility of electrons to be in the range 5-10 cm$^2$V$^{-1}$s$^{-1}$ and that for holes within 1-5 cm$^2$V$^{-1}$s$^{-1}$, where the variations depend on the crystal structure investigated and the level of doping. Such results, in good agreement with recent experiments, set the relaxation time to about 1 ps, which is the time-scale for the molecular rotation at room temperature. For the room temperature tetragonal phase we explore two possible orientations of the organic cations and find that the mobility has a significant asymmetry depending on the direction of the current with respect to the molecular axis. This is due mostly to the way the PbI$_3$ octahedral symmetry is broken. Interestingly we find that substituting I with Cl has minor effects on the mobilities. Our analysis suggests that the carrier mobility is probably not a key factor in determining the high solar-harvesting efficiency of this class of materials.
ADDITIONAL INFORMATION
The paper provides supplementary structural, electronic, conductivity, mobility, and simulation details for CH3NH3PbI3 phases and Cl-doped variants.
- Effective masses are calculated with and without SOC for holes and electrons.
- The tetragonal structures tetra1 and tetra2 are initialized with cations oriented along (001) and (110), respectively.
- The conductivity plots represent tensor components σxx, σyy, and σzz as functions of chemical potential.
- Average mobility is taken over the three diagonal components of the mobility tensor and is also plotted for Cl-doped perovskites.
- The molecular-dynamics analysis tracks chemical potential and elapsed time after a 5 ps equilibration phase, alongside total molecular polarization.