Tay Darrell J J, Febriansyah Benny, Salim Teddy, Kovalev Mikhail, Sharma Aakash, Koh Teck Ming, Mhaisalkar Subodh G, Ager Joel W, Mathews Nripan
Interdisciplinary Graduate Programme (IGP), Graduate College, Nanyang Technological University, Singapore, 637460, Singapore.
Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Singapore, 637553, Singapore.
Small. 2025 Feb;21(7):e2403389. doi: 10.1002/smll.202403389. Epub 2024 Aug 8.
Despite a recent shift toward methylammonium (MA)-free lead-halide perovskites for perovskite solar cells, high-efficiency formamidinium lead iodide (FAPbI) devices still often require methylammonium chloride (MACl) as an additive, which evaporates away during the annealing process. In this article, it is shown that the residual MA, however, triggers thermal instability. To investigate the possibility of an optimal concentration of MA that may improve thermal stability, the intrinsic thermal stability of pure FA, FA-rich, MA-rich, and pure MA perovskite films (FAMAPbI, FAMA) is studied. The results show that the thermal stability of FAMA perovskites decreases with more MA, under degradation conditions that isolate the intrinsic thermal stability of the material (i.e., without moisture and oxygen effects). X-ray diffraction (XRD), proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS), photoluminescence (PL) and UV-visible spectroscopy, and depth-profiling X-ray Photoelectron Spectroscopy (XPS) are employed to show that the observed trend is mainly due to the decomposition of the MA cation, as opposed to other effects such as the precursor solvent and film morphologies. It is also found that the surfaces of these FAMA films are MA rich, although this phenomenon does not appear to affect thermal stability. Finally, it is demonstrated that this trend is unaffected by the presence of Spiro-OMeTAD atop the film, and thus solar cell devices should preserve this trend.
尽管最近钙钛矿太阳能电池朝着不含甲铵（MA）的卤化铅钙钛矿转变，但高效的甲脒碘化铅（FAPbI）器件仍常常需要氯化甲铵（MACl）作为添加剂，而这种添加剂在退火过程中会挥发掉。然而，本文表明，残留的MA会引发热不稳定性。为了研究可能提高热稳定性的MA最佳浓度的可能性，对纯FA、富FA、富MA和纯MA钙钛矿薄膜（FAMAPbI、FAMA）的本征热稳定性进行了研究。结果表明，在隔离材料本征热稳定性的降解条件下（即无水分和氧气影响），FAMA钙钛矿的热稳定性随着MA含量的增加而降低。采用X射线衍射（XRD）、质子转移反应飞行时间质谱（PTR-ToF-MS）、光致发光（PL）和紫外可见光谱以及深度剖析X射线光电子能谱（XPS）来表明，观察到的趋势主要是由于MA阳离子的分解，而非其他效应，如前驱体溶剂和薄膜形态。还发现这些FAMA薄膜的表面富含MA，尽管这种现象似乎并不影响热稳定性。最后，证明了这种趋势不受薄膜顶部Spiro-OMeTAD存在的影响，因此太阳能电池器件应保持这种趋势。
