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

Perovskite-type hybrids (e.g., CH3NH3PbI3) 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 CH3NH3PbI3 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)3Sb2Cl9-9xBr9x (x = 0-1), showing large ferroelectric polarizations (5.2-7.6 μC/cm2) 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/cm2), 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.