Abstract
Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH2)2PbI3, HC(NH2)2PbBr3, CH3NH3PbI3 and CH3NH3PbBr3, and discover that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron–phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Fröhlich coupling constants of ∼40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites.
Highlights
Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites
Our results conclusively demonstrate that electron–phonon coupling in hybrid lead halide perovskites follows a classic bandstructure picture for polar inorganic semiconductors, which are dominated by Frohlich coupling between charge carriers and longitudinal optical (LO) phonon modes in the high-temperature regime
A further phase transition to the cubic phase follows at higher temperatures for the MA perovskites (at B330 K for MAPbI3 and 240 K for MAPbBr3), whereas a transition to a trigonal phase occurs at around 200 K for FAPbI3
Summary
Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Hybrid lead halide perovskites have attracted intense research activity following their first implementation as light absorbers in thin-film solar cells[1] that reach power conversion efficiencies (PCEs) in excess of 20% (refs 2,3) These compounds are described by the general formula ABX3, where A is typically an organic cation such as methylammonium (CH3NH3þ or MA þ ) B is a divalent metal ocratfioornm(aumsuidailnlyiuPmb2(Hþ C) (aNnHd 2X)2þisora. FA þ ), halide anion (I À , Br À or Cl À )[4] Such hybrid organic–inorganic materials straddle the divide between organic and inorganic semiconductors, facilitating photovoltaic devices that combine the low processing costs of the former with the high PCEs of the latter[2,3,5]. The success of hybrid perovskites in photovoltaic applications has been widely attributed to their high absorption coefficients across the visible spectrum[11], their low exciton binding energies[4,12] facilitating charge formation and their long charge-carrier diffusion lengths enabling efficient charge extraction[13,14]
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