| Abstract [eng] |
In recent years, hybrid lead halide perovskites have received exceptional attention in the scientific community due to their potential application in photovoltaic devices. Solar cells based on these hybrid compounds have already reached the power conversion efficiency of more than 20 %. Some of their useful properties are influenced by the structural phase transitions and cation dynamics. Many efforts have been devoted to study these materials with methods that are sensitive to structural changes and dynamic effects. Among many techniques used for characterization of crystal properties, nuclear magnetic resonance (NMR) spectroscopy is an exceptionally effective method in studying structural phase transitions and dynamics. In general, NMR is used to study the local magnetic and electric fields around atomic nuclei. This spectroscopic method has been successfully used multiple times to investigate lead halide perovskites. The aim of this work was to study the structural phase transition and cation dynamics in methylhydrazinium lead chloride (CH3NH2NH2PbCl3) perovskite. In order to achieve this goal, solid-state proton and lead-207 NMR spectroscopy was used. The results of this study were enough to prove the hypothesis about the order and type of the structural phase transition in CH3NH2NH2PbCl3 hybrid perovskite. Proton NMR experiments demonstrate that the ordering of methylhydrazinium cations is not the dominant phase transition mechanism in CH3NH2NH2PbCl3. This suggests a displacive type of the phase transition. Lead-207 NMR measurements show two signals, confirming two different lead-sites in the lead-chloride framework. This confirms the interesting two-layer structure of the lead chloride framework. And lastly, Lead-207 NMR experiments confirm that the phase transition is of the first-order with a displacive character and is mostly caused by the deformation of the lead-chloride framework. |
