Bandgap Narrowing of Lead-Free Perovskite-Type Hybrids for Visible-Light-Absorbing Ferroelectric Semiconductors

Perovskite-type hybrids (e.g., CH 3 NH 3 PbI 3 ) hold great promise in photovoltaics and optoelectronics due to their remarkable semiconducting properties and potential ferroelectricity. However, to date, conclusive evidence for the bulk ferroelectricity of CH 3 NH 3 PbI 3 is still lacking. In this context, it is highly desirable to assemble concrete perovskite ferroelectric hybrids with the semiconducting feature. Here we report, for the first time, a class of lead-free perovskite halides, ( N -methylpyrrolidinium) 3 Sb 2 Cl 9–9 x Br 9 x ( x = 0–1), showing large ferroelectric polarizations (5.2–7.6 μC/cm 2 ) and pronounced semiconducting performances. In particular, a wide tunability of their optical bandgaps (3.31–2.76 eV) enables superior visible-light-induced photocurrents (∼10 nA/cm 2 ), which allow for assembling of the crystal-based photodetectors. Our work paves a new way to build environmentally benign optoelectronic devices based on low-bandgap ferroelectric hybrids.