Whether or not methylammonium lead iodide (MAPbI3) is a ferroelectric
semiconductor has caused controversy in the literature, fueled by many
misunderstandings and imprecise definitions. Correlating recent literature
reports and generic crystal properties with the authors’ experimental
evidence, the authors show that MAPbI3 thin-films are indeed semiconducting
ferroelectrics and exhibit spontaneous polarization upon transition from the
cubic high-temperature phase to the tetragonal phase at room temperature.
The polarization is predominantly oriented in-plane and is organized in
characteristic domains as probed with piezoresponse force microscopy.
Drift-diffusion simulations based on experimental patterns of polarized
domains indicate a reduction of the Shockley–Read–Hall recombination of
charge carriers within the perovskite grains due to the ferroelectric built-in field
and allow reproduction of the electrical solar cell properties.