Direct Observation and Quantitative Analysis of Mobile Frenkel Defects in Metal Halide Perovskites Using Scanning Kelvin Probe Microscopy

Abstract

Ion migration is seen as a primary stability concern of halide perovskite-based photovoltaic and optoelectronic devices. Here, we provide experimental studies of long-distance, reversible ion migration in methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3) films. We use time-resolved scanning Kelvin probe microscopy on insulator-coated lateral electrodes to probe the dynamic redistribution of charged Frenkel defects over micrometer distances after application of an electric field. We combine these dynamic measurements with drift–diffusion simulations that yield self-consistent pictures of the sign, distribution, mobility, and activation energy of the associated, mobile Frenkel defects. This comprehensive approach is applied to study the impact of an organic cation on ionic mobility in metal halide perovskites, which we find to be significantly reduced in the case of FAPbI3 films compared to MAPbI3 films.

Unravelling the role of vacancies in lead halide perovskite through electrical switching of photoluminescence

“…Schottky defects indeed have been shown to have reasonably small formation energy 40 . However, very recently, Kelvin probe microscopy experiments using a similar lateral device geometry as in this work, show the major prevalence of Frenkel defects and their long-range motion in an electric field 27 , 41 .…”

Operational stability of perovskite light emitting diodes

“…Halide perovskites possess a mixed electronic and ionic conductivity [50,64]. To understand the ionic conductivity of perovskites, both experimental [35,[65][66][67] and theoretical [64,[68][69][70][71] studies have been conducted. Yuan et al observed the formation of PbI 2 at the anode side in a lateral device structure under an external bias and its propagation towards the cathode has been studied by energy-dispersive x-ray spectroscopy (EDX) mapping, which is a direct experimental evidence for halide ion migration [35].…”

How the formation of interfacial charge causes hysteresis in perovskite solar cells

“…We developed such a time-resolved method based on Kelvin probe force microscopy (KPFM) 3,4,[26][27][28][29][30][31] by decoupling the spatial mapping and the recording of the temporal evolution of the local contact potential difference (CPD). Thereby, we achieved sub-ms KPFM time resolution ( Fig.…”