911±¬ÁÏÍø

For hybrid perovskite research, CEST scientists and are collaborating with CNRS's neutron scattering group (led by Dr. David Djurado) in Grenoble, France and Dr. Mariana Rossi at Fritz Haber Institute of the Max Planck Society, Berlin. They studied the rotational dynamics of organic cations in the orthorhombic phase of CH3NH3PbI3. A theory-driven experimental-theoretical paper entitled "Activation Energy of Organic Cation Rotation in CH3NH3PbI3 and CD3NH3PbI3: Quasi-Elastic Neutron Scattering Measurements and First-Principles Analysis Including Nuclear Quantum Effects" (Jingrui Li, Mathilde Bouchard, Peter Reiss, Dmitry Aldakov, Stéphanie Pouget, Renaud Demadrille, Cyril Aumaitre, Bernhard Frick, David Djurado, Mariana Rossi and Patrick Rinke) has been published on .

The motion of CH3NH3+ cations in the low-temperature phase of the promising photovoltaic material methylammonium lead triiodide (CH3NH3PbI3) is investigated experimentally as well as theoretically, with a particular focus on the activation energy. Inelastic and quasi-elastic neutron scattering measurements reveal an activation energy of ~48 meV. Through a combination of experiments and first-principles calculations, we attribute this activation energy to the relative rotation of CH3 against a static NH3 group. The inclusion of nuclear quantum effects through path integral molecular dynamics gives an activation energy of ~42 meV, in good agreement with the neutron scattering experiments. For deuterated samples (CD3NH3PbI3), both theory and experiment observe a higher activation energy for the rotation of CD3 against NH3+, which results from the smaller nuclear quantum effects in CD3. The possibility that the rotation of the NH3 group (which is bound to the inorganic cage via strong hydrogen bonding) occurs at low temperatures is very low due to its high energy barrier of ~120 meV.