Emergence of bulk photovoltaic effect in anion-ordered perovskite sulfur diiodide MASbSI₂ with spontaneous out-of-plane ferroelectricity

Organic-inorganic halide perovskites composed of three-dimensional (3D) corner-sharing octahedral framework, represented by methylammonium lead iodide MAPbI₃, have attracted extensive research interests owing to their superior photovoltaic (PV) performance. On the other hand, taking advantage of spontaneous ferroelectricity and the associated bulk photovoltaic effect (BPVE), ferroelectric (FE)-PV materials are able to generate zero-bias photocurrent and above band gap photovoltage, offering the great promise for improved power conversion efficiency. However, FE nature of perovskite MAPbI₃ remains controversial. Alternatively, heteroanionic perovskite where the multiple anions of distinct sizes and valence states are in ordered arrangement, can create polar crystal structures with permanent electric polarization. In current work, we choose the experimentally reported perovskite methylammonium antimony sulfur diiodide MASbSI₂ as a prototypical example, and demonstrate trans S/I anion order and the stable out-of-plane ferroelectricity nearly independent of molecular dipoles from organic MA cations can be obtained in such a 3D organic-inorganic heteroanionic perovskite by first-principles calculations. The cooperative interplay of MA orientation, octahedral rotation, cation polar displacement and S/I anion arrangement that govern the origin and magnitude of ferroelectricity within MASbSI₂ have been thoroughly explored and well rationalized by our comprehensive first-principles calculations and electrostatic bond strength sum analysis. Especially, based on our electronic structure and nonlinear photo-current responses simulations, FE perovskite MASbSI₂ with combination of stable out-of-plane ferroelectricity up to 17.9 μC/cm², tunable semiconducting band gap, static Rashba effect and polarization controllable strong photocurrent responses within the visible light range, is demonstrated to be a long-sought 3D FE organic-inorganic perovskite material for efficient light-current conversion through BPVE.