Strong Carrier–Phonon Coupling in Lead Halide Perovskite Nanocrystals

Abstract

We highlight the importance of carrier–phonon coupling in inorganic lead halide perovskite nanocrystals. The low-temperature photoluminescence (PL) spectrum of CsPbBr3 has been investigated under a nonresonant and a nonstandard, quasi-resonant excitation scheme, and phonon replicas of the main PL band have been identified as due to the Fröhlich interaction. The energy of longitudinal optical (LO) phonons has been determined from the separation of the zero phonon band and phonon replicas. We reason that the observed LO phonon coupling can only be related to an orthorhombically distorted crystal structure of the perovskite nanocrystals. Additionally, the strength of carrier–phonon coupling has been characterized using the ratio between the intensities of the first phonon replica and the zero-phonon band. PL emission from localized versus delocalized carriers has been identified as the source of the observed discrepancies between the LO phonon energy and phonon coupling strength under quasi-resonant and nonresonant excitation conditions, respectively.

Low‐Temperature Absorption, Photoluminescence, and Lifetime of CsPbX3 (X = Cl, Br, I) Nanocrystals

“…Unlike single crystals, NCs may show an inhomogeneous linewidth due to variable environments (frequently observed as spectral diffusion in single particle measurements) and size dispersion, arising from quantum confinement effects, although these are expected to be weak for the NCs measured here . We do not observe any clear secondary features or shoulder of the PL at any temperature, despite earlier reports . Thermal broadening of PL at higher temperatures, plotted in Figure b, is accounted for using a Voight fit.…”

Impact of Small Phonon Energies on the Charge-Carrier Lifetimes in Metal-Halide Perovskites

“…In addition, SHR increases for larger values of E with the exception of very shallow negatively charged defects. Note that such large SHR values are not unprecedented 54 and not in conflict with recently reported, much smaller values for similar perovskite systems either, [55][56][57] as these experiments studied band-to-band transitions.…”

Hydrophobic Metal Halide Perovskites for Visible‐Light Photoredox C−C Bond Cleavage and Dehydrogenation Catalysis

“…Most interestingly, (HDA) 2 PbI 4 was still emissive when irradiated with UV while suspended in water, and the PL maximum was determined to be 500 nm (Figure d) after excitation at 350 nm. The modest Stokes shift is likely due to the high exciton binding energy, which leads to less energy loss by carrier–phonon interactions, and is often observed in low‐dimensional perovskites . However, (HDA) 2 SnI 4 did not exhibit the same stability, probably owing to the oxidation of Sn II to Sn IV .…”