Perspective: multi-dimensional coherent spectroscopy of perovskite nanocrystals

Abstract

Recently, colloidal perovskite nanocrystals (PNCs) have emerged as an exciting material platformfor optoelectronic applications due to their combination of facile synthesis routes, quantum size effects, and exceptional optical properties among other favorable characteristics. Given the focus on their optoelectronic properties, spectroscopic characterization of PNCs is crucial to rational design of their structure and device implementation. In this Perspective, we discuss how multi-dimensional coherent spectroscopy (MDCS) can resolve exciton dynamics and circumvent inhomogeneous broadening to reveal underlying homogeneous spectral lineshapes. We highlight recent applications of MDCS to PNCs in the literature, and suggest compelling problems concerning their microscopic physics to be addressed by MDCS in the future.

Measuring exciton-phonon coupling in semiconductor nanocrystals

“…Many interesting aspects of EPC in SNCs remain open for investigation, in particular with MDCS, and we give three examples of particular interest to us. First, characterizing the spectral density of EPC for more complicated unit cells than the simple case of CdSe [58], for example in perovskite nanocrystals [43], would be useful in relation to their unique optoelectronic properties. We have also observed the importance of dimensionality in 'freezing out' coupling to various vibrational modes [14,55,63], and further investigation of the dimensional cross-over would be useful for understanding the underlying mechanisms.…”

“…From our perspective, experimental measurements can inform design principles and constrain theoretical models, and are essential to advancing our understanding in this area. We have therefore reviewed common techniques for characterizing EPC in SNCs, and have also introduced multi-dimensional spectroscopy as a powerful new method to circumvent many limitations of traditional techniques [43]. These are summarized in table 1.…”

“…In recent years, a technique capable of measuring the entire complex nonlinear optical response has been developed, known as MDCS [5]. MDCS is an extension of sophisticated Fourier transform spectroscopies, originally developed for nuclear magnetic resonance, to optical frequencies, and has emerged as the preeminent method for disentangling complex dynamics in a wide range of materials ranging from molecules [40,41] to semiconductors [42,43], and even biological systems [44,45].…”

Measuring Exciton Fine-Structure in Randomly Oriented Perovskite Nanocrystal Ensembles Using Nonlinear Optical Spectroscopy: Theory

“…Two-dimensional coherent spectroscopy (2DCS), or more generally multidimensional coherent spectroscopy [ 25 , 26 , 27 ], is a nonlinear spectroscopic technique capable of resolving all dimensions of a complex-valued nonlinear optical response. As the name implies, a 2-D spectrum is obtained that reflects a cross section of along two spectral axes.…”

Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy

“…The many-body correlations between excitons and carriers manifest in the nonlinear optical response of the materials, specifically in the evolution in the spectral lineshapes in the ultrafast timescales. Two-dimensional coherent spectroscopy is the technique of preference for disentangling such many-body correlations in bulk and nanostructured semiconductors [17][18][19][20][21][22][23].…”