Giant bandgap renormalization and exciton-phonon scattering in perovskite nanocrystals

Abstract

Understanding the interactions between photoexcited charge carriers (electrons and holes) with lattice vibrations (phonons) in quantum confined semiconductor nanocrystals (NCs) is of fundamental interest and a prerequisite for their use in fabricating high-performance optoelectronic devices. Such interactions have a significant impact on their optoelectronic properties including their charge carrier mobility and photoluminescence. Here, we investigate these interactions in cesium lead halide (CsPbX3, where X is Cl, Br or I) NC perovskites. We show that a wide broadening of the excitonic linewidth in these NCs arises from strong exciton-phonon coupling, which is substantially dominated by longitudinal optical phonons via the Fröhlich interaction. Unlike the behavior of conventional semiconductors these NCs display a general red-shift of their emission energy peak with reducing temperature. Interestingly, the CsPbCl3 NCs also display an initial blue-shift and undergo at structural phase transition at ~175 K to 200 K. The anomalous red-shift observed is modeled and analyzed using a Bose-Einstein two-oscillator model to interpret the interaction of excitons with acoustic and optical phonons which induce a renormalization of the bandgap. The net renormalization due to zero point motion (T= 0 K) was found to be ~41.6 meV and ~94.9 meV for CsPbBr3 and CsPbI3 NCs respectively.

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ORCID for Antonios Kanaras: orcid.org/0000-0002-9847-6706

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