The Unprecedented Highest‐Layer‐Number Ferroelectric Semiconductor of 2D Homologous Single‐Phase Perovskites Tailored by Regulating Thickness of Inorganic Frameworks

Abstract Ferroelectric semiconductors represent an exciting branch of new‐generation optoelectronic devices. However, regarding severe polarization deterioration caused by leakage current, it is challenging to couple ferroelectricity and semiconductive properties in a single‐phase material. The first quadrilayered ferroelectric semiconductor of 2D homologous perovskites, IA₂Cs₃Pb₄Br₁₃ (IA = isoamylammonium), showing distinctive ferroelectric characteristics of symmetry breaking at 351 K and large polarization of 4.2 µC cm^‐2 is presented here. The design strategy of increasing layer‐number endows higher Curie temperature and superior semiconductor merits than other lower‐layered members (IA₂Cs_n‐1Pb_nBr_3n+1, n = 1–3). Bulk photovoltaic effects in IA₂Cs₃Pb₄Br₁₃ result in a notable dichroism up to ≈1.2 for self‐driven polarized‐light detection. This unprecedented study opens an avenue toward the targeted performance optimization of electric‐ordered functional materials.