Crystal Growth, Structural Phase Transitions, and Optical Gap Evolution of CH3NH3Pb(Br1- xClx)3 Perovskites

ALVAREZ-GALVÁN, M.C.; ALONSO, J.A.; LÓPEZ, C.A.; LÓPEZ-LINARES, E.; CONTRERAS, C.; LÁZARO, M.J.; FAUTH, F.; MARTÍNEZ-HUERTA, M.V.

CRYSTAL GROWTH & DESIGN

AMER CHEMICAL SOC

Año: 2019 vol. 19 p. 918 - 924

1528-7483

Chemically tuned inorganic-organic hybrid halide perovskites based on bromide and chloride anions CH3NH3Pb(Br1-xClx)3 have been crystallized and investigated by synchrotron X-ray diffraction (SXRD), scanning electron microscopy, and UV-vis spectroscopy. CH3NH3PbBr3 and CH3NH3PbCl3 experience successive phase transitions upon cooling, which are suppressed for intermediate compositions probably due to compositional disorder. For CH3NH3PbCl3, a transient phase, formerly described as tetragonal, was identified at 167.5 K; the analysis of SXRD data demonstrated that it is indeed orthorhombic, with space group Pnma, and a ≈ √ 2ap; b ≈ 2ap; c ≈ √ 2ap (ap is the ideal cubic perovskite unit-cell parameter). The band gap engineering brought about by the chemical management of CH3NH3Pb(Br1-xClx)3 perovskites can be controllably tuned: the gap progressively increases with the concentration of Cl ions from 2.2 to 2.9 eV, and shows a concomitant variation with the unit-cell parameters of the cubic phases at 295 K. This study provides an improved understanding of the structural and optical properties of the mixed CH3NH3Pb(Br1-xClx)3 perovskites.