Cation local orientation effect on the optical properties in quasi- cubic hybrid perovskites MA1-xFAxPbI3

S. TINTE; M. SENNO

Buenos Aires

Simposio; 1st Symposium Perovskite materials and Solar cells; 2020

CAC - CNEA

Currently, the best performing perovskite materials for solar cells contain multiple cations and provide power conversion efficiencies up to around 22%. In this work, we use first-principles methods to elucidate the effect played by the orientation of the organic cation and its local arrangement in the double-cation perovskite alloy methylammonium (CH3NH3+,MA) - formamidinium (CH(NH22)2+,FA) lead iodine, MA1-xFAxPbI3, on the optical properties. We consider two representative compositions (x=0.125 and 0.875) to compare with the parent compounds MAPbI3 and FAPbI3, and study the cation preferred arrangement. Our results reveal a preferential perpendicular alignment along the MA+ and FA+ cations located at nearest neighbor A sites in the alloy. Specifically the MA+ dipole moment prefers to point toward the plane defined by the FA+ cations. Interestingly, that perpendicular orientation among nearest-neighbor organic molecules is also found in both pure compounds MAPI and FAPI when a large computational supercell is used instead of the one-single motif cells as done in most ab-initio studies. In the talk, I will discuss how this preferential orientation effects the dielectric function spectra.