Long-lived polarization memory in the electronic states of lead-halide perovskites from local structural dynamics

Jasmine P H Rivett,Andrew M Rappe,Felix Deschler,James Xiao,Baoquan Sun,Sean A Bourelle,Rox Middleton,Michael B Price,Nathaniel J L K Davis,Yatao Zou,Dan Credgington,Liang Z Tan

doi:10.1038/s41467-018-06009-3

Abstract

Anharmonic crystal lattice dynamics have been observed in lead halide perovskites on picosecond timescales. Here, we report that the soft nature of the perovskite crystal lattice gives rise to dynamic fluctuations in the electronic properties of excited states. We use linear polarization selective transient absorption spectroscopy to study the charge carrier relaxation dynamics in lead-halide perovskite films and nanocrystals. We find that photo-excited charge carriers maintain an initial polarization anisotropy for several picoseconds, independent of crystallite size and composition, and well beyond the reported timescales of carrier scattering. First-principles calculations find intrinsic anisotropies in the transition dipole moment, which depend on the orientation of light polarization and the polar distortion of the local crystal lattice. Lattice dynamics are imprinted in the optical transitions and anisotropies arise on the time-scales of structural motion. The strong coupling between electronic states and structural dynamics requires a unique interpretation of recombination and transport mechanisms.

Highlights

Anharmonic crystal lattice dynamics have been observed in lead halide perovskites on picosecond timescales
We use linear polarization selective transient absorption spectroscopy (LP-TA) to investigate how the reported crystal dynamics affect the electronic states occupied by photoexcited carriers in lead halide perovskite thin films with organic and inorganic A-site cations (CH3NH3PbX3, X = I, Br, CsPbBr3) and nanocrystals (CsPbI3) at room temperature
We report an optically excited picosecond transient anisotropy in the electronic states of lead halide perovskites

Summary

Introduction

Anharmonic crystal lattice dynamics have been observed in lead halide perovskites on picosecond timescales. Their excellent photovoltaic performance derives from the perovskites’ band-like semiconducting behavior, with high absorption coefficients[2] in the range of 105 cm−1, combined with long carrier lifetimes[3,4] These materials lie between the extremes of highly-ordered, crystalline semiconductors, which can exhibit ballistic charge transport, and disordered, molecular semiconductors, where strong electron–phonon coupling leads to highly localized excited states. We use linear polarization selective transient absorption spectroscopy (LP-TA) to investigate how the reported crystal dynamics affect the electronic states occupied by photoexcited carriers in lead halide perovskite thin films with organic and inorganic A-site cations (CH3NH3PbX3, X = I, Br, CsPbBr3) and nanocrystals (CsPbI3) at room temperature This method is sensitive to the coupling between the optical polarization vector of the absorbed light and the transition dipole matrix (TDM) element of the electronic states, which allows us to probe optical anisotropies in the excited state population. Optical alignment is lost on the timescales of local structural reorientation rather than diffusion

Methods

Results

Conclusion