Understanding the precursor chemistry for one-step deposition of mixed cation perovskite solar cells by methylamine route

Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization. The slow evaporation of frequently used solvents (DMF or DMSO) limits the fast perovskite layer crystallization, hindering their implementation in large scale deposition methods. Alternatively, methylamine-based precursors have demonstrated rapid crystallization, leading to uniform and specular films. Nonetheless, their application has been limited to MAPbI(3) perovskites with limited efficiency and stability. In this work, we report the requirements for stabilizing alpha-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor. We found that even though, there are many methods for incorporating the methylamine (MA) in precursors or films; the MA content determines stabilization of the alpha-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA. At low amounts of MA, perovskite tend to crystallize in 1D dimensional FA(3)(MA)PbI5 phases due to the incomplete solvation of the PbI6 clusters. In contrast, high MA ratio induces a full solvation of the clusters, leading to a rapid crystallization and a full stabilization of the active 3D alpha-phase. These results open a window in the development and understanding of new precursors for the fabrication of high efficient, stable and scalable perovskite devices. (C) 2020 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

This study investigates the requirements for stabilizing high amounts of methylamine and formamidinium mixed cation perovskite alpha-phase using a methylamine-based precursor. The viscous-solution route is found to be the only method to incorporate high amounts of methylamine. High methylamine ratio leads to rapid crystallization and full stabilization of the active 3D alpha-phase, while low amounts of methylamine tend to result in crystallization in 1D dimensional phases.