A 2D hybrid perovskite ferroelectric with switchable polarization and photoelectric robustness down to monolayer

The continuous dimensional scaling of semiconductor and logic photoelectric device requires ferroelectrics to possess robust photoelectric activity and switchable polarization at the nanoscale. However, traditional ferroelectrics such as oxide perovskites generally suffer from relatively large bandgap and deteriorated ferroelectricity in ultrathin forms, while the polarization in many transition metal dichalcogenides is related to inter-layer effects, leading to ferroelectricity that only exists in flakes with a certain layer number and particular stacking forms. The associated challenging fabrication and high-cost synthesis of inorganic ferroelectrics currently render mass industrial production of ultrathin ferroelectric semiconductors impossible. Here with (isopentylammonium)2(ethylammonium)2Pb3I10, we report an organic-inorganic hybrid perovskite nanoflake with cheap solution synthesis, switchable polarization, a narrow bandgap (1.86 eV to 2.21 eV form bulk to monolayer), and robust photoelectric properties down to the monolayer. The present work reveals the great potential of 2D hybrid perovskite ferroelectrics as low-cost ferroelectric semiconductors at the nanoscale.