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

Abstract

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)₃Sb₂Cl_9-9xBr_9x (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.