Franssen Wouter M J, van Heumen Cathy M M, Kentgens Arno P M
Magnetic Resonance Research Center, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
Inorg Chem. 2020 Mar 16;59(6):3730-3739. doi: 10.1021/acs.inorgchem.9b03380. Epub 2020 Mar 2.
Recently, a number of variations to the hybrid perovskite structure have been suggested in order to improve on the properties of methylammonium lead iodide, the archetypical hybrid halide perovskite material. In particular, with respect to the chemical stability of the material, steps should be taken. We performed an in-depth analysis of the structure of MAPbI upon incorporation of dimethylammonium (DMA) in order to probe the integrity of the perovskite lattice in relation to changes in the organic cation. This material, with formula MADMAPbI, adopts a 3D perovskite structure for 0 < < 0.2, while a nonperovskite yellow phase is formed for 0.72 < < 1. In the perovskite phase, the methylammonium and dimethylammonium ions are distributed randomly throughout the lattice. For 0.05 < < 0.2, the phase-transition temperature of the material is lowered when compared to that of pure MAPbI ( = 0). The material, although disordered, has apparent cubic symmetry at room temperature. This leads to a small increase in the band gap of the material of about 20 meV. Using N NMR relaxation experiments, the reorientation times of the MA and DMA cations in MADMAPbI were established to be 1.6 and 2.6 ps, respectively, indicating that both ions are very mobile in this material, on par with the MA ions in MAPbI. All of the produced MADMAPbI materials were richer in DMA than the precursor solution from which they were crystallized, indicating that DMA incorporation is energetically favorable and suggesting a higher thermodynamic stability of these materials when compared to that of pure MAPbI.
最近，为了改进典型的混合卤化物钙钛矿材料——甲基碘化铅铵的性能，人们提出了多种混合钙钛矿结构的变体。特别是在材料的化学稳定性方面，应采取相应措施。我们对掺入二甲基铵（DMA）后的MAPbI结构进行了深入分析，以探究钙钛矿晶格相对于有机阳离子变化的完整性。这种化学式为MADMAPbI的材料，在0 << 0.2时采用三维钙钛矿结构，而在0.72 << 1时形成非钙钛矿黄色相。在钙钛矿相中，甲基铵离子和二甲基铵离子在整个晶格中随机分布。对于0.05 << 0.2，与纯MAPbI（ = 0）相比，该材料的相变温度降低。该材料虽然无序，但在室温下具有明显的立方对称性。这导致材料的带隙小幅增加，约为20 meV。通过N NMR弛豫实验，确定MADMAPbI中MA和DMA阳离子的重取向时间分别为1.6和2.6 ps，这表明两种离子在这种材料中都非常活跃，与MAPbI中的MA离子相当。所有制备的MADMAPbI材料中的DMA含量都比其结晶所用的前驱体溶液中的DMA含量高，这表明掺入DMA在能量上是有利的，并且表明与纯MAPbI相比，这些材料具有更高的热力学稳定性。
