Giant Bandgap Renormalization and Exciton–Phonon Scattering in Perovskite Nanocrystals

• Published in: Advanced optical materials 2017-09, Vol.5 (17), p.n/a
• Main Authors: Saran, Rinku, Heuer‐Jungemann, Amelie, Kanaras, Antonios G., Curry, Richard J.
• Format: Article
• Language: English
• Subjects: bandgap renormalization; Carrier mobility; Cesium; cesium lead halides; Current carriers; Emissions control; Excitation; Excitons; exciton–phonon interactions; Lattice vibration; Materials science; Nanocrystals; Optics; Optoelectronic devices; Perovskites; Phase transitions; Phonons; Photoluminescence; Red shift
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.201700231

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, these interactions are investigated in cesium lead halide (CsPbX3, where X is Cl, Br, or I) NC perovskites. It is shown 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 redshift of their emission energy peak with reducing temperature. Interestingly, the CsPbCl3 NCs also display an initial blueshift and undergo at structural phase transition at ≈175–200 K. The anomalous redshift 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) is found to be ≈41.6 and ≈94.9 meV for CsPbBr3 and CsPbI3 NCs, respectively. Exciton–phonon interactions in cesium lead halide nanocrystals (NCs) are investigated through the analysis of their temperature‐dependent steady‐state photoluminescence spectra. Experimental results are modeled to explain the thermal broadening of photoluminescence exciton linewidth and anomalous temperature dependence of the bandgap in CsPbX3 NCs.