Interfacial Passivation of Perovskite Solar Cells by Reactive Ion Scavengers

Lead halide perovskites suffer from uncontrolled ion migration and the interactions at the external contacts play a fundamental role in the hysteretic response and performance degradation kinetics. In this work, we passivate the external interfaces by a reaction of migrating iodide ions with a silver buffer layer placed between Spiro-OMeTAD and Au layers. In the presence of an electrical field, iodine migration occurs and ions that are close to the perovskite/contact interface irreversibly form a layer of AgI. Overall, the interfacial reaction of iodide ions totally suppresses hysteresis and leads to more stable devices. A new sample preparation method unburies the reactive interface, which is then probed by X-ray photoelectron spectroscopy measurements. The kinetics of the layer formation are monitored by impedance spectroscopy highlighting that in the presence of an electrical field and light, the reaction occurs in the order of minutes. We further identify the resistive response of AgI in operating devices. The present work provides a new approach to passivate the external interfaces in lead halide perovskites.