We investigated the structural properties of organic–inorganic lead halide perovskite microwires through joint experimental and theoretical Raman spectroscopy. High-quality methyl ammonium lead iodide (MAPBI3, MA = CH3NH3+) microwires with tetragonal phases and explicit crystalline orientation were prepared. Raman spectroscopy was used in studying the as-prepared microwires and determining not only the crystal quality but also crystalline orientation of MAPBI3 with the aid of normal mode calculations. High-quality structural features were verified by well-resolved Raman peaks related to the inorganic cage (I-Pb-I stretching and bending modes below 100 cm−1), organic MA cation motions (libration ~150–200 cm−1 and torsional ~200–250 cm−1), a coupled mode of cage and MA cation liberation (~105–110 cm−1), and the almost undetectable degraded signal at 95 cm−1. In micro-Raman mapping, an intensity ratio of 105 and 95 cm−1 was used for the direct imaging of crystal quality along the microwire. The characterization of the crystalline orientation of MAPBI3 microwires posed a challenge, which can be addressed by using polarized Raman technique with normal mode analysis. We believe that the proposed method can be extended to other organic–inorganic lead halide perovskites with different structures, such as polycrystalline films and single crystals.
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