Hope Michael A, Mishra Aditya, Emsley Lyndon
Department of Chemistry, University of Warwick, Coventry CV4 7AL, United Kingdom.
Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Chem Mater. 2024 Jul 24;36(15):7525-7532. doi: 10.1021/acs.chemmater.4c01498. eCollection 2024 Aug 13.
Ion migration is an important phenomenon affecting the performance of hybrid perovskite solar cells. It is particularly challenging, however, to disentangle the contribution of H diffusion from that of other ions, and the atomic-scale mechanism remains unclear. Here, we use H exchange NMR to prove that H ions exchange between MA cations on the time scale of seconds for both MAPbI and FAMAPbI perovskites. We do this by exploiting N-enriched MA to label the cations by their N spin state. The exchange rates and activation energy are then calculated by performing experiments as functions of mixing time and temperature. By comparing the measured exchange rates to previously measured bulk H diffusivities, we demonstrate that, after dissociating, H ions travel through the lattice before associating to another cation rather than hopping between adjacent cations.
离子迁移是影响混合钙钛矿太阳能电池性能的一个重要现象。然而，要区分氢扩散与其他离子扩散的贡献尤其具有挑战性，其原子尺度的机制仍不清楚。在这里，我们使用氢交换核磁共振（NMR）来证明，对于MAPbI和FAMAPbI钙钛矿，氢原子在几秒钟的时间尺度内在甲铵（MA）阳离子之间进行交换。我们通过利用富含氮的MA，根据其氮自旋态来标记阳离子，从而实现这一点。然后通过进行作为混合时间和温度函数的实验来计算交换速率和活化能。通过将测量的交换速率与先前测量的体相氢扩散率进行比较，我们证明，在离解后，氢原子在与另一个阳离子结合之前先穿过晶格，而不是在相邻阳离子之间跳跃。
