Critical Comparison of FAPbX₃ and MAPbX₃ (X = Br and Cl): How Do They Differ?

Abstract

Dielectric measurements on formamidinium lead halide perovskites, FAPbCl3 and FAPbBr3, compared to those of MAPbCl3 and previously reported MAPbBr3, reveal the strongly suppressed temperature dependence of dielectric constants in FA compounds in the temperature range of approximately 140–300 K. Although the behavior of dielectric constants of FA compounds for temperatures <140 K resembles that of the MAPbX3 system, the absence of any strong temperature dependence in sharp contrast to MA analogues in the higher temperature range up to room temperature suggests that the formamidinium (FA) dipoles are in a deep-frozen glassy state unlike the MA dipoles that rotate nearly freely in the temperature range relevant for any photovoltaic application. This observation is further supported by the temperature-dependent single-crystal X-ray diffraction (XRD) results.

A piperidinium salt stabilizes efficient metal-halide perovskite solar cells

“…These peaks were fitted to a cubic unit cell in the Pm3 ̅ m space group and could not be fitted with the unit cells of any of the relevant binary halide salts. For the modified sample aged at 360 h the cubic unit cell has a volume of 217(1) Å 3 , which is within error of the reported volume of FAPbBr3 (217.45(2) Å 3 ) (20). We indicate the XRD peaks associated with this second phase by ( ǂ) in Figs.…”

Stable Whispering Gallery Mode Lasing from Solution‐Processed Formamidinium Lead Bromide Perovskite Microdisks

“…The power X‐ray diffraction (XRD, Figure 1d) pattern of as‐grown microdisks matches well with the reported XRD pattern of FAPbBr 3 single crystal. [ 20 ] In addition, qualitative elemental analysis of individual microdisk shows that the molar ratio of Pb:Br:N element is basically in accordance with the stoichiometric ratio of FAPbBr 3 (Figure S3, Supporting Information). These results indicate that obtained square and quasi‐circular microdisks are pure FAPbBr 3 phase without any impurities.…”

“…[ 16–19 ] FAPbBr 3 has two crystallographic phases of cubic and trigonal crystal system. [ 20 ] Compared with the yellow emission (≈587 nm) of millimeter sized FAPbBr 3 single crystals, FAPbBr 3 films and microcrystals show green emission (≈550 nm). [ 21 ] This may be attributed to the intrinsic band gap of 2.15 eV in fully crystallized 3D FAPbBr 3 lattice, which is tighter in bulk single crystals than that in thin films and low‐dimensional microcrystals.…”

“…Theoretically, the FAPbBr 3 perovskites can grow into square, trigonal or hexagonal microdisks under suitable crystallization process due to their intrinsic cubic and trigonal crystal system. [ 20 ] Therefore, as the increased concentration of precursors, antisolvent or temperature‐induced supersaturation, these micro‐ and nanospheres transform to square and quasi‐circular shapes depending on their intrinsic cubic and trigonal crystal system, respectively. For the formation of square FAPbBr 3 microdisk, with slow consumption of solid Pb(Ac) 2 film, the formed low‐concentration Pb precursor (PbBr 4 2− ) combined with FA + in precursor solution to maintain a low supersaturation condition for the crystal growth of FAPbBr 3 .…”

Tracking Structural Phase Transitions in Lead‐Halide Perovskites by Means of Thermal Expansion

“…The results obtained for δ‐FAPbI 3 and FAPbBr 3 are presented in Figures and with the phase transition temperatures and phases specified in Tables 1 and 2 , respectively. It should be noted that previous studies of the crystal structure as derived from variable temperature single crystal/powder XRD studies of FAPbBr 3 gave contradictory conclusions . We first focus on δ‐FAPbI 3 in Figure a.…”