Temperature-Dependent Evolution of Raman Spectra of Methylammonium Lead Halide Perovskites, CH₃NH₃PbX₃ (X = I, Br)

Abstract

We present a Raman study on the phase transitions of organic/inorganic hybrid perovskite materials, CH3NH3PbX3 (X = I, Br), which are used as solar cells with high power conversion efficiency. The temperature dependence of the Raman bands of CH3NH3PbX3 (X = I, Br) was measured in the temperature ranges of 290 to 100 K for CH3NH3PbBr3 and 340 to 110 K for CH3NH3PbI3. Broad ν1 bands at ~326 cm−1 for MAPbBr3 and at ~240 cm−1 for MAPbI3 were assigned to the MA⁻PbX3 cage vibrations. These bands exhibited anomalous temperature dependence, which was attributable to motional narrowing originating from fast changes between the orientational states of CH3NH3+ in the cage. Phase transitions were characterized by changes in the bandwidths and peak positions of the MA⁻cage vibration and some bands associated with the NH3+ group.

Keywords

• Raman spectroscopy
• phase transition
• motional narrowing
• bandwidth
• organic/inorganic hybrid perovskites
• methylammonium lead halide perovskites