Terahertz Vibrational Modes in CH3NH3PbI3 and CsPbI3 Perovskite Films

Films of CH3NH3PbI3 organometallic perovskite, which is currently considered as a promising basic material for new-generation solar cells, as well as films containing CsPbI3 inorganic lead-halid perovskite nanocrystals, have been studied in the spectral range of 0.2-2.9 THz at room temperature by terahertz time-domain spectroscopy. Several low-frequency vibrational modes previously attributed exclusively to vibrations of Pb-I bonds have been observed in the perovskite films under investigation in this spectral range. The comparison of terahertz characteristics of perovskites under study has shown that vibrations associated with a cation (CH3 NH3+, Cs+) make a significant contribution to the formation of the observed low-frequency vibrational modes in perovskites under consideration.