Ultrafast infrared spectroscopy reveals intragap states in methylammonium lead iodide perovskite materials

Organic-inorganic hybrid materials have recently attracted a lot of attention for optoelectronic applications as they allow combining the flexibility and processibility of organic molecular systems with the good stability and charge-transport properties of inorganic crystalline materials. In this contribution, we report on the use of ultrafast vis-pump / infrared(IR)-probe spectroscopy to investigate the optical signature of charge carrier dynamics in CH₃NH₃PbI₃ perovskite films. We observed that this perovskite shows a complex response which involves strong ground-state bleach contribution. This behaviour differs from most inorganic semiconductors and quantum dot materials that show strong photoinduced absorption in IR upon carrier generation,. The bleaching probably results from a partial filling of intragap states next to the conduction band edge. It may also indicate the existence of a Burstein–Moss type effect in perovskite materials.