Diversity of band gap and photoluminescence properties of lead halide perovskite: A halogen-dependent spectroscopic study

The effects of halogen substitution on microstructure, optical absorption, and phonon modes for perovskite CH₃NH₃PbX₃(MAPbX₃, X = I/Br/Cl) films grown on FTO substrates have been investigated. The X-ray diffraction analysis exhibited good crystallization, and the strong diffraction peak assigned to (100)_c for X = Br/Cl shifted toward a higher angle compared to (110)_t of MAPbI₃. Band-gap tuning from 1.63 to 2.37 to 3.11 eV in the I-Br-Cl series can be found due to the halogen effects. These energy values closely match the positions of peak determined from photoluminescence experiments. The remarkable absorption dip and emission peak appear for the MAPbBr₃, suggesting higher crystallinity under the same preparation conditions. The wavenumbers of main IR-vibrations slightly decrease with ionic radius of the halogen increasing (in the order of Cl-Br-I), which related to the increasing polarizability. These results provide important progress towards the understanding of the halide role in the realization of high performance MAPbX₃-based solar cells.