Schuck, G.; Lehmann, F.; Ollivier, J.; Mutka, H.; Schorr, S.: Influence of Chloride Substitution on the Rotational Dynamics of Methylammonium in MAPbI3–xClx Perovskites. The Journal of Physical Chemistry C 123 (2019), p. 11436-11446
Open Accesn Version

Hybrid halide perovskites, MAPbI3, MAPbI2.94Cl0.06, and MAPbCl3 (MA, methylammonium), were investigated using inelastic and quasielastic neutron scattering (QENS) with the aim of elucidating the impact of chloride substitution on the rotational dynamics of MA. In this context, we discuss the influence of the inelastic neutron scattering caused by low-energy phonons on QENS, resulting from the MA rotational dynamics in MAPbI3–xClx. Through a comparative temperature-dependent QENS investigation with different energy resolutions, which allow a wide Fourier time window, we achieved a consistent description of the influence of chlorine substitution in MAPbI3 on the MA dynamics. Our results showed that chlorine substitution in the low-temperature orthorhombic phase leads to a weakening of the hydrogen bridge bonds, since the characteristic relaxation times of C3 rotation at 70 K in MAPbCl3 (135 ps) and MAPbI2.94Cl0.06 (485 ps) are much shorter than that in MAPbI3 (1635 ps). For the orthorhombic phase, we obtained the activation energies from the temperature-dependent characteristic relaxation times τ C3 by Arrhenius fits, indicating lower values of Ea for MAPbCl3 and MAPbI2.94Cl0.06 compared to that of MAPbI3. We also performed QENS analyses at 190 K for all three samples. Here, we observed that MAPbCl3 shows slower MA rotational dynamics than MAPbI3 in the disordered structure.