Ferroelectricity and Crystal Phases in Mixed‐Cation Lead Iodide Perovskite Solar Cells

Abstract

After the discovery of ferroelectricity in archetypal methylammonium lead iodide (MAPbI3), the discussion arose, if more advanced derivatives thereof are also ferroelectric and to what extent the polar domains mitigate detrimental charge carrier recombination in perovskite solar cells. Herein, the A‐site cation methylammonium is gradually substituted with formamidinium and cesium. The domain contrast measured by piezoresponse force microscopy is correlated with the distortion of the crystal structure measured by X‐ray diffraction. By Rietveld analysis, a detailed structural model together with texture information is determinded, which reveals an intriguing interplay between lead iodide and the perovskite phases. Finally, the bearing of ferroelectric domains in mixed‐cation perovskites on the solar cell performance is discussed.