Ions Matter: Description of the Anomalous Electronic Behavior in Methylammonium Lead Halide Perovskite Devices

Carrier transport in methylammonium lead iodide (MAPbI(3))-based hybrid organic-inorganic perovskites (HOIPs) is obscured by vacancy-mediated ion migration. Thus, the nature of migrating species (cation/anion) and their effect on electronic transport in MAPbI(3) has remained controversial. Temperature-dependent pulsed voltage-current measurements of MAPbI(3) thin films are performed under dark conditions, designed to decouple ion-migration/accumulation and electronic transport. Measurement conditions (electric-field history and scan rate) are shown to affect the electronic transport in MAPbI(3) thin films, through a mechanism involving ion migration and accumulation at the electrode interfaces. The presence of thermally activated processes with distinct activation energies (E-a) of 0.1 +/- 0.001 and 0.41 +/- 0.02 eV is established, and are assigned to electromigration of iodine vacancies and methylammonium vacancies, respectively. Analysis of activation energies obtained from electronic conduction versus capacitive discharge shows that the electromigration of these ionic species is responsible for the modification of interfacial electronic properties of MAPbI(3), and elaborates previously unaddressed issues of "fast" and "slow" ion migration. The results demonstrate that the intrinsic behavior of MAPbI(3) material is responsible for the hysteresis of the solar cells, but also have implications for other HOIP-based devices, such as memristors, detectors, and energy storage devices.