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.

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Li-rich cathode materials are potential candidates for next generation Li-ion batteries. However, they exhibit large voltage hysteresis on the 1 st charge/discharge cycle involving a substantial (up to 1V) loss of voltage and therefore energy density. For Na cathodes, e.g. Na0.75[Li0.25Mn0.75]O2, voltage hysteresis can be explained by formation of molecular O2 trapped in voids within the particles. Here we show that this is also the case for Li1.2Ni0.13Co0.13Mn0.54O2. RIXS and 17 O MAS NMR show that molecular O2, rather than O2 2-, forms within the particles on oxidation of O 2at 4.6 V vs Li + /Li on charge. These O2 molecules are reduced back to O 2on discharge but at the lower voltage of 3.75 V explaining the voltage hysteresis in Li-rich cathodes. 17 O MAS NMR indicates a quantity of bulk O2 consistent with the O-redox charge capacity minus the small quantity of O2 loss from the surface. The implication is that O2, trapped in the bulk and lost from the surface, can explain O-redox.