A polar two-dimensional lead-free hybrid perovskite for self-powered polarization-sensitive photodetection

Abstract

Two-dimensional (2D) lead hybrid perovskites have attracted great attention due to their excellent stability and unique physical and chemical properties. Nevertheless, the toxicity of lead remains an urgent issue. Lead-free homovalent substituents (Sn²⁺and Ge²⁺) suffer from poor oxygen-sensitive stability, posing a serious challenge to their device applications. Compared to homovalent substituents, heterovalent substituted perovskites based on the VA group elements, especially bismuth, exhibit excellent stability, making them more competitive. However, 2D Bi-based perovskites with the composition 2D A₂BiX₄ (A = organic cation; X = Cl⁻, Br⁻ or I⁻) cannot be formed considering the charge balance. Here, by reducing the occupancy rate of Bi³⁺ ions, we successfully obtained the first polar 2D Bi-based perovskite (4BrPEA)₃BiI₆ (4BrPEA = 4-bromophenethylammonium) with an A₂PbX₄-like layered structure. (4BrPEA)₃BiI₆ exhibits a narrow bandgap (2.00 eV) and excellent photoelectric response performance. Specifically, a single crystal device based on (4BrPEA)₃BiI₆ has been explored for self-powered polarization-sensitive photodetection with a large photocurrent anisotropic ratio ω of 2.16. This work demonstrates the great potential of heterovalent substituted 2D lead-free perovskites and opens up a new way to expand the synthesis of environmentally friendly and high-performance self-powered polar optoelectronic semiconductor materials.