Two-dimensional (2D) multilayer Dion–Jacobson (DJ) phase organic inorganic hybrid perovskites (OIHPs) have attracted extensive research attention due to the high stability and excellent charge-transport properties in the optoelectronic field. However, the synthesis of 2D multilayer DJ OIHPs is still very challenging. Until now, only few multilayer DJ perovskites have been reported and most of them are based on volatile methylamine (MA) cations. Compared with MA-based OIHPs, the OIHPs constructed with formamidinium (FA) as perovskitizers not only improve the stability but also extend the light absorption range. Meanwhile, the introducing aromatic diamines as spacers could promote the electron–hole separation in such DJ hybrids. However, the DJ OIHP bulk single crystal constructed by using the advantages of FA as perovskitizers and aromatic diamines as spacers is still blank. Herein, we integrate the properties of organic cations and inorganic skeletons at a molecular-scale to construct a broadband-responsive 2D bilayer DJ perovskite (3AMPY)­(FA)­Pb2I7 [3AMPY = 3-(aminomethyl)­pyridinium], which shows a fascinating detectivity from X-ray (5.23 × 104 μC Gyair –1 cm–2 at 200 V bias) and visible light (6 × 1012 jones at 637 nm) to the near-infrared region (2.6 × 109 jones at 780 nm). After an in-depth analysis of structure and optical properties, we found that the distortion degree of Pb–I–Pb bond angles between adjacent PbI6 octahedra plays a crucial role on optical properties; on the other hand, the interlayer spacer cations (3AMPY) and intralayer perovskitizers (FA) mutual participate in the contribution of the conduction band, making (3AMPY)­(FA)­Pb2I7 have a narrow optical band gap of 1.54 eV. Such a 2D perovskite material with a wide spectra response will be the preferred choice for photodetection under complex conditions.

Organic–inorganic lead-iodide perovskites are attracting tremendous interest because of their great application potential in optoelectronics and photovoltaics. Despite extensive interest, however, no lead-iodide perovskites have been found as multiaxial multiferroic materials with the coexistence of full ferroelectricity and full ferroelasticity. Here, based on the ferroelastic [EQ]­PbI3 (EQ = N-ethyl-quinuclidine) with an Aizu notation of 6/mmmF2/m, we introduced a hydroxyl group to N-ethyl-quinuclidine and successfully synthesized a homochiral lead-iodide perovskite multiaxial multiferroic [(R)-N-ethyl-3-quinuclidinol]­PbI3 ([R-EQ]­PbI3). [R-EQ]­PbI3 undergoes a phase transition at 380 K from 622 to 2 point groups, and thereby it is a multiaxial full ferroelectric and also a multiaxial full ferroelastic in the room-temperature phase according to the Aizu notation of 622F2(s). Multiple equivalent ferroelectric/ferroelastic axes can endow [R-EQ]­PbI3 with a larger polarization/strain in the polycrystalline samples. This work presents the first multiaxial full multiferroic in lead-iodide perovskites, which would inspire further exploration of chiral perovskite multiferroics for applications such as high precision microdisplacement devices and variable surface acoustic wave delay lines.

Two-dimensional (2D) Dion–Jacobson (DJ) hybrid perovskites with exceptional stability and enhanced out-of-plane carrier transport are regarded as one of the competive candidates for constructing next-generation photodetectors. However, the studies of DJ hybrid perovskites on weak light detection remain scarce, and the devices based on them usually show relatively poor weak light detection ability, with a detection limit of around μW/cm2. Herein, a new DJ hybrid perovskite (3AMPY)(MA)Pb2Br7 [3AMPY is 3-(aminomethyl)pyridinium, and MA is methylammonium] with short interlayer spacing and more lattice rigidity is obtained. The devices based on (3AMPY)(MA)Pb2Br7 crystals exhibit an ultrahigh sensibility to weak light at 377 and 405 nm, with an extremely low detection limit of ∼70 nW/cm2. Moreover, the on/off ratios and detectivity of the devices can reach ∼103 and ∼1012 Jones at both 377 and 405 nm, respectively. This work highlights great potential of DJ hybrid perovskites toward weak light detection.

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