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

We present a Raman study on the phase transitions of organic/inorganic hybrid perovskite materials, CH 3NH 3PbX 3 (X = I, Br), which are used as solar cells with high power conversion efficiency. The temperature dependence of the Raman bands of CH 3NH 3PbX 3 (X = I, Br) was measured in the temperature ranges of 290 to 100 K for CH 3NH 3PbBr 3 and 340 to 110 K for CH 3NH 3PbI 3. Broad ν 1 bands at ~326 cm ？1 for MAPbBr 3 and at ~240 cm ？1 for MAPbI 3 were assigned to the MA–PbX 3 cage vibrations. These bands exhibited anomalous temperature dependence, which was attributable to motional narrowing originating from fast changes between the orientational states of CH 3NH 3 + 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 NH 3 + group. View Full-Tex