Temperature Dependence of the Energy Levels of Methylammonium Lead Iodide Perovskite from First-Principles

Abstract

Environmental 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 CHNHPbI 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 CHNHPbI 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 CsPbI. Our results unambiguously confirm for the first time the importance of high-order terms in the electron-phonon coupling by direct comparison with experiment.

Structural dynamics in hybrid halide perovskites: Bulk Rashba splitting, spin texture, and carrier localization

“…10, we can conclude that the dynamic structural disorder opens up the band gap substantially as also noticed by Saidi et al [50] and McKechnie et al [30]. After opening, the band gap continues to change dynamically with fluctuations of ∼ 0.3 eV that is consistent with literature [28,50]. It is interesting to note that the band gap renormalization of such a large magnitude due to the structural dynamic is inherent to wide band gap materials only.…”

“…By observing changes in the band gap in Fig. 10, we can conclude that the dynamic structural disorder opens up the band gap substantially as also noticed by Saidi et al [50] and McKechnie et al [30]. After opening, the band gap continues to change dynamically with fluctuations of ∼ 0.3 eV that is consistent with literature [28,50].…”

Perspective: Theory and simulation of hybrid halide perovskites

“…The method includes quantum nuclear motion, goes beyond the harmonic regime, but only contains the first-order contribution to the electron-phonon coupling of the bandgap deformation. A positive bandgap shift of 36 meV (R point phonon) and 28 meV (M point phonon) is predicted at T = 300 K. Saidi et al sampled all non-soft harmonic phonons using a Monte Carlo technique, 46 finding significant differences with (more standard) perturbation theory results. Electron-phonon interactions can be calculated with MD, but as with phonon-phonon scattering, achieving convergence with respect to electronic (k -point sampling and basis set) and vibrational (q-point sampling and supercell size), while maintaining sufficient integration time to capture rare processes, is costly.…”

Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination

“…Previous studies have shown that temperature plays a notable effect on solar efficiency such as decreasing the open-circuit voltage V oc of MAPbI 3 -based solar cells from 1.01 to 0.83 V as the temperature increases from 300 to 360 K (25). In part, V oc drop could be due to the renormalization of the band gap of MAPbI 3 with temperature, which is of the order of 30 to 40 meV in the temperature range of solar cell operation (26)(27)(28)(29). In addition, the degradation of PCE with temperature could be due to enhancements in the inelastic scattering between defect and charged carriers, as these are mediated by electron-phonon coupling.…”