(C H NH ) (NH CHNH )Pb I : A Two-dimensional Bilayer Inorganic-Organic Hybrid Perovskite Showing Photodetecting Behavior.

Inorganic-organic hybrid perovskites, especially two-dimensional (2D) layered halide perovskites, have attracted significant attention due to their unique structures and attractive optoelectronic properties, which open up a great opportunity for next-generation photosensitive devices. Herein, we report a new 2D bilayered inorganic-organic hybrid perovskite, (C H NH ) (NH CHNH )Pb I (HFA, where C H NH is hexylaminium and NH CHNH is formamidinium), which exhibits a remarkable photoresponse under broadband light illumination. Structural characterizations demonstrate that the 2D perovskite structure of HFA is constructed by alternant stacking of inorganic lead iodide bilayered sheets and organic hexylaminium layers. Optical absorbance measurements combined with density functional theory (DFT) calculations suggest that HFA is a direct band gap semiconductor with a narrow band gap (E ) of ≈2.02 eV. Based on these findings, photodetectors based on HFA crystal wafer are fabricated, which exhibit fascinating optoelectronic properties including large on/off current ratios (over 10 ), fast response speeds (τ =310 μs and τ =520 μs) and high responsivity (≈0.95 mA W ). This work will contribute to the design and development of new two-dimensional bilayer inorganic-organic hybrid perovskites for high-performance photosensitive devices.