Methylammonium lead iodide exhibits spectacular photovoltaic performance with solar cell efficiencies over 19%. However, there remains significant controversy over the existence of ferroelectricity and its impact on the photovoltaic response in these materials. In this work, we confirm the presence of ferroelectricity in methylammonium lead iodide single crystals through d33 piezoelectric measurements, band excitation piezoresponse force microscopy with concurrent contact Kelvin probe force microscopy, DFT calculations, and temperature dependent Rayleigh analysis. Large signal poling greater than 16 V/cm induced permanent ferroelectric domains up to 40 µm wide. Poling lead to a distinguishable domain specific electronic response identified by scanning microwave impedance microscopy and electric force microscopy. The domain specific response is further corroborated by XPS, which does not show any indications of a change in surface chemistry in the material before and after poling. The poled crystals also show domain specific preferential stabilization (or etching) over a period of weeks. Routes to use this ferroelectric response to increase device stability, improve photovoltaic performance, and develop new functionalities will be discussed.
–
Publication: 1. L. M. Garten, D. Moore, S. Nanayakkara, S. Dwaraknath, P. Schulz, B. Newell, K. Persson, S. Trolier-McKinstry, D. S. Ginley (2019). The Existence and Impact of Persistent Ferroelectric Domains in MAPbI3. Science Advances, 5(1), eaas9311. https://doi.org/10.1126/sciadv.aas9311. <br>2. Garten, Lauren Marie, Moore, David Todd, Ginley, David Samuel, and Gorman, Brian Patrick. Hybrid perovskite bulk photovoltaic effect devices and methods of making the same. United States: Patent, 2020.
