Excited state and charge transfer dynamics in gas phase molecule of CH₃NH₃PbI₃: first-principles study

In this work, to probe the charge transfer mechanism of methylammonium lead triiodide (CH₃NH₃PbI₃), we have used density functional theory (DFT) and time-dependent density functional theory (TDDFT). We investigate ground and excited states optimized geometry, UV-vis spectrum and vibrational frequencies of CH₃NH₃PbI₃ molecule. It is observed that in an excited state, the structural change is mostly localized in PbI₃ part of the molecule. Mulliken charge analysis shows that lead (Pb) atom acquires a maximum positive charge and all iodine atoms get a negative charge. In addition to this, all the hydrogen atoms donate their charge to iodine atoms. Therefore, electron transfer from lead (Pb) and hydrogen atoms to the iodine atoms can be considered as a significant charge transfer mechanism. Vibrational frequencies are obtained and assigned with the help of hessian calculations. Vibrational mode at 225 cm^-1 is identified as the NH₃-I stretching.