Differing Effects of Mixed A-Site Composition on the Properties of Hybrid Lead Iodide Perovskites

Halide perovskites (HPs) appeared as a revolu-tionary class of relevant optoelectronic materials. Optimizing these materials involves developing mixed formulations currently used in many of the most efficient HP-based devices. Mixing A-site organic cations has been a widely used strategy to achieve the desired characteristics in these perovskites. Few of the reported works were devoted to understanding the effects of different organic cations on the properties of the resulting HPs. In the present work, we report a detailed study on the structural, thermal, and electrical properties and degradation assays in HPs with mixing A-site organic cations at the MAPbI3, FA0.10MA0.90PbI3, GA0.10MA0.90PbI3, and GA0.05FA0.05MA0.90PbI3 compositions. The results show that the charge transport properties change consistently with the A-site cation size. However, the structure and phase transitions are unusually affected by the composition, suggesting that other characteristics of substituent cations are relevant to the behavior of the resulting materials. Finally, thermal degradation tests reveal that, contrary to general expectations, not all mixed compositions are more stable than their related pure HPs. More than that, the order of degradation kinetics may also depend on the type of substituent cation. The results elucidate the particularities of each type of organic cation on the properties of mixed perovskites and advance knowledge about these relevant materials.