Cordero Francesco, Craciun Floriana, Paoletti Anna Maria, Zanotti Gloria
Istituto di Struttura della Materia-CNR (ISM-CNR), Area della Ricerca di Roma, Tor Vergata, Via del Fosso del Cavaliere 100, I-00133 Rome, Italy.
Istituto di Struttura della Materia-CNR (ISM-CNR), Area della Ricerca di Roma 1, Via Salaria Km 29.300, Monterotondo Scalo, I-00015 Rome, Italy.
Nanomaterials (Basel). 2021 Jun 18;11(6):1610. doi: 10.3390/nano11061610.
We studied the influence of water on the structural stability and transformations of MAPI and FAPI by anelastic and dielectric spectroscopies under various temperature and H2O partial pressure protocols. Before discussing the new results in terms of interstitial water in MAPI and FAPI, the literature is briefly reviewed, in search of other studies and evidences on interstitial water in hybrid halide perovskites. In hydrated MAPI, the elastic anomaly between the cubic α and tetragonal β phases may be depressed by more than 50%, demonstrating that there are H2O molecules dispersed in the perovskite lattice in interstitial form, that hinder the long range tilting of the PbI6 octahedra. Instead, in FAPI, interstitial water accelerates in both senses the reconstructive transformations between 3D α and 1D δ phases, which is useful during the crystallization of the α phase. On the other hand, the interstitial H2O molecules increase the effective size of the MA and FA cations to which are bonded, shifting the thermodynamic equilibrium from the compact perovskite structure to the open δ and hydrated phases of loosely bonded chains of PbI6 octahedra. For this reason, when fabricating devices based on hybrid metal-organic halide perovskites, it is important to reduce the content of interstitial water as much as possible before encapsulation.
我们通过滞弹性和介电谱研究了在不同温度和水蒸汽分压条件下水对MAPI和FAPI结构稳定性及转变的影响。在根据MAPI和FAPI中的间隙水讨论新结果之前，先简要回顾一下文献，以寻找关于混合卤化物钙钛矿中间隙水的其他研究和证据。在水合MAPI中，立方α相和四方β相之间的弹性异常可能会降低50%以上，这表明有以间隙形式分散在钙钛矿晶格中的水分子，阻碍了PbI6八面体的长程倾斜。相反，在FAPI中，间隙水在两个方向上都加速了3D α相和1D δ相之间的重构转变，这在α相结晶过程中是有用的。另一方面，间隙水分子增加了与之键合的MA和FA阳离子的有效尺寸，将热力学平衡从紧密的钙钛矿结构转移到由PbI6八面体松散键合链组成的开放δ相和水合相。因此，在制造基于混合金属有机卤化物钙钛矿的器件时，在封装之前尽可能降低间隙水的含量非常重要。
