Optical detection of charge dynamics in CH₃NH₃PbI₃/carbon nanotube composites

We have investigated the optical absorption of metallic and semiconducting carbon nanotubes/CH₃NH₃PbI₃ micro- and nanowire composites. Upon visible light illumination semiconducting carbon nanotube based samples show a photo-induced doping, originating from the charge carriers created in the perovskite while this kind of change is absent in the composites containing metallic nanotubes, due to their strikingly different electronic structure. The response in the nanotubes shows, beside a fast diffusion of photo-generated charges, a slow component similar to that observed in pristine CH₃NH₃PbI₃ attributed to structural rearrangement, and leading to slight, light induced changes of the optical gap of the perovskite. This charge transfer from the illuminated perovskite confirms that carbon nanotubes (especially semiconducting ones) can form efficient charge-transporting layers in the novel organometallic perovskite based optoelectronic devices.