Two-dimensional electronic spectroscopy reveals liquid-like lineshape dynamics in CsPbI3 perovskite nanocrystals

Abstract

Lead-halide perovskites have attracted tremendous attention, initially for their performance in thin film photovoltaics, and more recently for a variety of remarkable optical properties. Defect tolerance through polaron formation within the ionic lattice is a key aspect of these materials. Polaron formation arises from the dynamical coupling of atomic fluctuations to electronic states. Measuring the properties of these fluctuations is therefore essential in light of potential optoelectronic applications. Here we apply two-dimensional electronic spectroscopy (2DES) to probe the timescale and amplitude of the electronic gap correlations in CsPbI3 perovskite nanocrystals via homogeneous lineshape dynamics. The 2DES data reveal irreversible, diffusive dynamics that are qualitatively inconsistent with the coherent dynamics in covalent solids such as CdSe quantum dots. In contrast, these dynamics are consistent with liquid-like structural dynamics on the 100 femtosecond timescale. These dynamics are assigned to the optical signature of polaron formation, the conceptual solid-state analogue of solvation.

Electronic States Modulation by Coherent Optical Phonons in 2D Halide Perovskites

“…For the former, which is our case, it is pertinent to the solvation of excited state by the optical lattice displacement (i.e., similar to polar solvation in liquids). [ 66 ] In general, a small S (<1) indicates weak coupling and carrier localization, and thus formation of a large polaron, suggesting that carriers may be protected from scattering by defects and other carriers. For the latter that occurs in polar semiconductors, the polaron coupling constant α is given as: where ε ∞ and ε S are respectively, the electronic and static dielectric constants, ε 0 is the vacuum permittivity, m is the effective mass, e is the electric unit, ℏ is the reduced Planck constant, and ω LO is the LO phonon frequency.…”

Decoding ultrafast polarization responses in lead halide perovskites by the two-dimensional optical Kerr effect

“…In analogy to other 2D spectroscopy methods (4,(20)(21)(22)(23)(24)(25)(26)(27), we use a phase-stable double pump-pulse sequence to implement 2D-OKE, Fig. 1A.…”

“…multidimensional coherent spectroscopy | four-wave mixing | nonlinear polarization | lead halide perovskites | light propagation U nderstanding the ultrafast polarization response to light fields and the subsequent generation of charge carriers or excitons is key to establishing the photophysical mechanisms in the excellent optoelectronic material system of lead halide perovskites (LHPs) (1). The two ionic polarization contributions by the reorientational motion of organic cations and the deformation of the inorganic cages have been discussed within dynamic screening models (2)(3)(4) and large polaron formation (5), respectively and jointly, whereas the immediate electronic polarization response to the light field itself has been neglected so far. In many optoelectronic applications, nevertheless, not only charge carrier transport but also light propagation right below the bandgap is essential.…”

Investigating the electronic structure of confined multiexcitons with nonlinear spectroscopies

“…[24][25][26][27] Most recently, two-dimensional electronic spectroscopy (2DE) experiments have been performed on these model systems. [28][29][30][31][32][33] Since MX in QD remain an interesting test bed for exploring many-body physics and for their continued relevance in new nanomaterials from perovskites [34][35][36][37][38][39][40][41] to transition metal dichalcogenides, [42][43][44][45][46][47][48][49] one aims for a comprehensive overview of the methods for investigation and their critical comparison. Here, we report on such an overview of the experimental signatures of MX in CdSe NCs using the three main methods: t-PL, SRPP, and 2DE.…”