Monolayer‐to‐Multilayer Dimensionality Reconstruction in a Hybrid Perovskite for Exploring the Bulk Photovoltaic Effect Enables Passive X‐ray Detection

Abstract Halide hybrid perovskites are attracting considerable attention as highly promising candidates for directly sensing X‐ray radiation, but it is challenging to realize passive X‐ray detection without an external power supply. However, the bulk photovoltaic effect (BPVE) in ferroelectrics promotes the independent separation of photoexcited carriers. Herein, by dimensionality reconstruction of a pure‐two‐dimensional (P‐2D) monolayered perovskite (CH 3 OC 3 H 9 N) 2 PbBr 4 , we obtained a quasi‐two‐dimensional (Q‐2D) ferroelectric (CH 3 OC 3 H 9 N) 2 CsPb 2 Br 7 . Converting P‐2D into Q‐2D perovskite stimulates a significant BPVE associated with robust ferroelectricity, as well as an enhanced mobility lifetime product. These features show the potential of the first passive X‐ray detector based on ferroelectrics with an impressive sensitivity up to 410 μC Gy −1 cm −2 at zero bias, which is even superior to the value of the state‐of‐the‐art α‐Se detector operated at relatively high bias.