The dominant role of surfaces in the hysteretic behavior of hybrid perovskites. (January 2020)

• Record Type: Journal Article
• Authors: Caddeo, Claudia; Filippetti, Alessio; Mattoni, Alessandro
• Is Part Of: Nano energy. Volume 67(2020)
• Publication Date: 2020-01
• Subjects: Defects -- Simulations -- Model potential -- Polarization -- Memory effects; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2019.104162
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Hysteresis and memory-effects are an issue for the development of a reliable solar technology based on hybrid perovksites. In this context, we study the effect of surfaces on the electric mobility of charged point-defects at room conditions by molecular dynamics simulations. At variance with the bulk, for which the ionic current is linear and reversible upon inversion of the electric field, we find that the presence of surfaces gives rise to accumulation of charged point-defects and memory effects. Surfaces act as trapping regions for iodine defects with fast accumulation and much slower release kinetics (by at least two orders of magnitude). The calculated release times are of hundreds of millisecond for both vacancies and interstitials at MAI- and PbI2 -terminated surfaces, respectively and are consistent with the decays of ionic currents observed in time-resolved Kelvin Probe Force Microscopy experiments. As we do not find ferroelectric polarization and memory effects on ionic currents in perfect crystalline bulks at room conditions, we conclude that surfaces (and likely interfaces or boundaries) are key factors giving rise to hysteresis. Present results are complemented by an analytic model of the effect of surfaces on point defects and of the kinetics of ionic polarization for the design of functional films with better control of hysteretic ionic currents. Graphical abstract: Image 1 Highlights: Hysteresis and memory effects in hybrid perovskites are determined by the effect of surfaces and interfaces on ionic dynamics. Surfaces act as trapping regions for highly mobile iodine point-defects. The slow release of point-defects from surfaces is at the origin of hysteresis. Surface-defects interaction is calculated by classical molecular dynamics and fitted by analytical models. Present results can help the design of hysteresis-free perovskites layers.