Ferroelectricity free lead halide perovskites

Direct piezoelectric force microscopy DPFM is employed to examine whether or not lead halide perovskites exhibit ferroelectricity. Compared to conventional piezoelectric force microscopy, DPFM is a novel technique capable of measuring piezoelectricity directly. This fact is fundamental to be able to examine the existence of ferroelectricity in lead halide perovskites, an issue that has been under debate for several years. DPFM is used to detect the current signals, i.e. changes in the charge distribution under the influence of the scan direction and applied force of the atomic force microscope AFM tip in contact mode. For comparison, i we use DPFM on lead halide perovskites and well known ferroelectric materials i.e. periodically poled lithium niobate and lead zirconate titanate ; and ii we conduct parallel experiments on MAPbI3 films of different grain sizes, film thicknesses, substrates, and textures using DPFM as well as piezoelectric force microscopy PFM and electrostatic force microscopy EFM . In contrast to previous work that claimed there were ferroelectric domains in MAPbI3 perovskite films, our work shows that the studied perovskite films Cs0.05 FA0.83MA0.17 0.95Pb I0.83Br0.17 3 and MAPbI3 are ferroelectricity free. The observed current profiles of lead halide perovskites possibly originate from ion migration that happens under an applied electrical bias and in strained samples under mechanical stress. This work provides a deeper understanding of the fundamental physical properties of the organic inorganic lead halide perovskites and solves a longstanding dispute about their non ferroelectric character an issue of high relevance for optoelectronic and photovoltaic application