The room-temperature charge carrier mobility and excitation-emission properties of metal halide perovskites are governed by their electronic band structures and intrinsic lattice phonon scattering mechanisms. Establishing how charge carriers interact within this scenario will have far-reaching consequences for developing high-efficiency materials for optoelectronic applications. Herein we evaluate the charge carrier scattering properties and conduction band environment of the double perovskite Cs2AgBiBr6 via a combinatorial approach; single crystal X-ray diffraction, optical excitation and temperature-dependent emission spectroscopy, resonant and nonresonant Raman scattering, further supported by first-principles calculations. We identify deep conduction band energy levels and that scattering from longitudinal optical phonons-via the Fröhlich interaction-dominates electron scattering at room temperature, manifesting within the nominally nonresonant Raman spectrum as multiphonon processes up to the fourth order. A Fröhlich coupling constant nearing 230 meV is inferred from a temperature-dependent emission line width analysis and is found to be extremely large compared to popular lead halide perovskites (between 40 and 60 meV), highlighting the fundamentally different nature of the two "single" and "double" perovskite materials branches.
Bibliographical noteFunding Information:
The authors acknowledge financial support from the Research Foundation-Flanders (FWO, grant nos. G.0962.13, G.0B39.15, G.0197.11, and ZW15_09 GOH6316, postdoctoral fellowships to J.A.S., H.Y., and E.D.), KU Leuven Research Fund (C14/ 15/053), the Flemish government through long term structural funding Methusalem (CASAS2, Meth/15/04), the Hercules foundation (HER/11/14), and the Belgian Federal Science Policy Office (IAP-VII/05). The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC grant agreement (grant no. 307523), ERC-Stg LIGHT to M.B.J.R. C.W.K and N.H.H. acknowledge the Pohang Light Source, Korea, for the use of their diffractometers and computing facilities.
© 2018 American Chemical Society.
- Fröhlich interactions
- Raman scattering
- conduction band resonance
- double perovskite