Chemical bonding of formamidinium (FA) with the inorganic perovskite skeleton of FAPbX3 (X = Br, I) is studied with emphasis on the differences to methylammonium: stronger hydrogen bonding, the presence of π-anion bonding, and more sterically hindered motion inside the perovskite inorganic cage. Organic cation dopants fitting in the perovskite cubic cell and being capable of hydrogen and halogen bonding with overall doubled bonding strength as compared to FA are proposed. They are shown to suppress not only X-migrations but also the undesirable α–δ phase transition of FAPbI3. In addition, a possible atomistic explanation of the champion solar cell efficiency achieved experimentally is developed.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors would like to acknowledge valuable discussions with Sumit Ghosh. The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). For computer time, this research used the resources of the Supercomputing Laboratory at KAUST. All figures were created using VESTA.