Abstract
Morphology and chemical composition of the CH3NH3PbI3 films on bare glass and indium tin oxide (ITO) are investigated. The film on bare glass is smoother with a narrow grain size distribution, while the one on ITO is rougher with a large grain size distribution. Energy-dispersive X-ray and X-ray photoelectron spectra reveal that there is a superstoichiometric ratio of CH3NH3+ cations in the upper part of the CH3NH3PbI3 film deposited on ITO. Such a chemical composition segregation originates from the higher affinity of PbI2 to ITO. It is demonstrated that the CH3NH3+ cations can migrate to cathode under applied positive bias, which forms an ionic conductivity and increases the current of the device. Thus the device is in a high conductivity state. A large number of CH3NH3+ cations accumulated near the cathode forms a build-in electric field with a direction opposite to the external field. This restricts further migration of the CH3NH3+ cations and the device turns to a low conductivity state. The migration and accumulation of the CH3NH3+ cations manipulate the device to switch between the high and low conductivity states, endowing the device working as a memristor.
NSTL
Elsevier