Suppression of phase transitions and glass phase signatures in mixed cation halide perovskites

Abstract

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.

Mixed Dimethylammonium/Methylammonium Lead Halide Perovskite Crystals for Improved Structural Stability and Enhanced Photodetection

“…Evolution of the CNC stretching and rocking modes of DMA [ 20,49 ] in terms of Raman shift (peak position) and linewidth (FWHM) as a function of temperature in the 44% DMA crystals. The dotted lines mark the phase‐transition temperatures.…”

Guanidinium substitution-dependent phase transitions, ionic conductivity, and dielectric properties of MAPbI3

“…A similar trend was observed in DMA + -substituted MAPbBr 3 perovskites, for which the increasing of DMA + content eventually led to the suppression of the low-temperature phase transition. 28 Although the reasons for these changes in GA x-MA 1Àx PbI 3 are unknown, the fact that the e 0 peak cannot be seen in the GA 0.2 MA 0.8 PbI 3 composition in the temperature range studied suggests that guanidinium also causes an alteration in the low temperature phase transitions of MAPbI 3 .…”

Temperature-Dependent Raman Studies of FAPbBr3 and MAPbBr3 Perovskites: Effect of Phase Transitions on Molecular Dynamics and Lattice Distortion

“…Single crystals of MAPbBr 3 (FAPbBr 3 ) with dimensions up to 10 mm were grown from mixtures containing PbBr 2 , acetonitrile, DMSO, HBr and a methanol solution of methylamine (formamidinium acetate) by antisolvent vapour-assisted crystallization using methyl acetate as the antisolvent (further details can be found in [11,24]).…”

“…X-ray diffraction data showed that MAPbBr 3 exhibits three phase transitions at 236, 153 and 144 K, which lead to a decrease of symmetry from cubic (Pm3m) to tetragonal I (I4/mcm), tetragonal II (P4/mmm) and orthorhombic (Pnma), respectively [22][23][24][25]. However, very recent X-ray diffraction data suggested that the intermediate phase, ascribed previously to the tetragonal phase II, has incommensurately modulated structure with the average space group Imma [26].…”