Room-Temperature Photoferroelectrics Semiconductor Driven by the Interlayer Confinement Effect

With the assistance of the ferroelectrochemistry theory, many multifunctional organic–inorganic hybrid perovskites (OIHPs) ferroelectrics have been designed and studied. However, research on regulating ferroelectrics through the interlayer confinement effect in two-dimensional (2D) OIHPs is still rare. Herein, we regulated the strength of interlayer confinement by changing the length of the alkyl chain on organic cations, and precisely constructed a lead bromide ferroelectric (IPA)2PbBr4 (IPA+ is isopropylammonium) with a high Curie temperature (Tc) of 340.5 K and a spontaneous polarization (Ps) of 3.16 μC/cm2 through a strong interlayer confinement effect. Compared with (IPA)2PbBr4 (Tp = 370.5 K), (IBA)2PbBr4 (IBA+ is isobutylammonium, Tp = 315 K) and (IAA)2PbBr4 (IAA+ is isoamylammonium, Tp = 271 K) crystallized in the centrosymmetric space group P21/c, Cmca at room temperature (RT), respectively, while also having a lower phase transition temperature (Tp). More importantly, the gradual decrease in interlayer spacing from 10.47 Å in (IAA)2PbBr4, 7.73 Å in (IBA)2PbBr4 to 5.79 Å in (IPA)2PbBr4 enhances the interlayer confinement effect, leading to IBA+ and IAA+ cations in a disordered state at RT, while the IPA+ cation can be arranged in an orderly and directional manner. Due to the differences in cations configuration, the impacts on the degree of distortion of inorganic skeleton and PbBr6 octahedra are also different, ultimately reflected in the crystal structure. In short, the directional arrangement and order–disorder phase transition of IPA+ cations induce the ferroelectricity of (IPA)2PbBr4 through the strong confinement effect of the inorganic skeleton. Additionally, a single crystal device based on (IPA)2PbBr4 was assembled, which exhibits a lower X-ray detection limit of 102 nGy/s in the self-driven mode. This work provides an effective strategy for designing high-temperature photoferroelectrics semiconductors.