Search

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 applications., The authors gratefully acknowledge the Spanish Ministerio de Economía, Industria y Competitividad for its support through Grant No. MAT2015-70850-P, PGC2018-095411-B-I00 and SEV-2015-0496 in the framework of the Spanish Severo Ochoa Centre of Excellence program and through Grant MAT2015-70850-P (HIBRI2). We thank the financial support from the European Research Council through project ERC CoG648901. We thank the Program under grant agreement No. 654360 within the framework of NFFA-Europe that benefits us with access to ICMAB-CSIC in Barcelona. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). A. A. thanks the National Natural Science Foundation of China under the grant number 21750110442.