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Metal halide perovskites have outperformed conventional inorganic semiconductors in direct X-ray detection due to their ease of synthesis and intriguing photoelectric properties. However, the operational instability caused by severe ion migration under a high external electric field is still a big concern for the practical application of perovskite detectors. Here, we report a 2D (BPEA) 2 PbI 4 (BPEA = R -1-(4-bromophenyl)ethylammonium) perovskite with Br-substituted aromatic spacer capable of introducing abundant interactions, e.g., the molecular electrostatic forces between Br atoms and aromatic rings and halogen bonds of Br-I, in the interlayer space, which effectively suppresses ion migration and thus enables superior operational stability. Constructing direct X-ray detectors based on high-quality single crystals of (BPEA) 2 PbI 4 results in a high sensitivity of 1,003 μC Gy -1 cm -2 , a low detection limit of 366 nGy s -1 , and an ultralow baseline drift of 3.48 × 10 -8 nA cm -1 s -1 V -1 at 80 V bias. More strikingly, it also exhibits exceptional operational stability under high flux, long-time X-ray irradiation, and large working voltage. This work shows an integration of multiple interlayer interactions to stabilize perovskite X-ray detectors, providing new insights into the future design of perovskite optoelectronic devices toward practical application., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Chemiresistive sensing has been regarded as the key monitoring technique, while classic oxide gas detection devices always need an external power supply. In contrast, the bulk photovoltage of photoferroelectric materials could provide a controllable power source, holding a bright future in self-powered gas sensing. Herein, we present a new photoferroelectric ([ n -pentylaminium] 2 [ethylammonium] 2 Pb 3 I 10 , 1 ), which possesses large spontaneous polarization (∼4.8 μC/cm 2 ) and prominent visible-photoactive behaviors. Emphatically, driven by the bulk photovoltaic effect, 1 enables excellent self-powered sensing responses for NO 2 at room temperature, including extremely fast response/recovery speeds (0.15/0.16 min) and high sensitivity (0.03 ppm -1 ). Such figures of merit are superior to those of typical inorganic systems (e.g., ZnO) using an external power supply. Theoretical calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements confirm the great selectivity of 1 for NO 2 . As far as we know, this is the first realization of ferroelectricity-driven self-powered gas detection. Our work sheds light on the self-powered sensing systems and provides a promising way to broaden the functionalities of photoferroelectrics.

Halide perovskite heterocrystals, composed of distinct perovskite single crystals, have generated great interest for both fundamental research and applied device designs. One of the key advantages of using such a heterocrystal is its built-in electric potential, which enhances charge transport and suppresses the noise in the solid-state devices. On the basis of this strategy, high-performance optoelectronic devices (e.g., X-ray detectors) have been successfully demonstrated. However, the toxicity of metal cations (Pb) in those reported heterocrystals hinders their wider applications. Thus, developing lead-free halide perovskite heterocrystals is significant but remains highly challenging. Here, we report a solution-processed in situ heteroepitaxial approach that enables us to create the first lead-free halide perovskite heterocrystal, (BA) 2 CsAgBiBr 7 /Cs 2 AgBiBr 6 (BA = n -butylammonium), with dimensions of up to 10 × 7 × 6 mm 3 . The as-grown heterocrystals have high crystalline quality and present near atomically sharp interfaces. More excitingly, the (BA) 2 CsAgBiBr 7 /Cs 2 AgBiBr 6 heterogeneous integration allows the formation of a built-in electric potential in the junction, which triggers spontaneous charge separation/transport. Consequently, X-ray detectors using the heterocrystals can operate in a self-driven mode and exhibit an impressive sensitivity (206 μC Gy -1 cm -2 ) superior to that of the pristine Cs 2 AgBiBr 6 crystal detectors, an ultralow dark current, and operational stability. Our findings provide the first demonstration of lead-free halide perovskite heterocrystals and may open up opportunities for a host of sustainable and miniaturized perovskite optoelectronic devices.

High-Curie-temperature ( T c ) ferroelectrics have exhibited broad applications in optoelectronic devices. Recently, two-dimensional multilayered perovskite ferroelectrics with excellent photoelectric attributes are attracting increasing interest as new systems of photoferroelectrics. However, the effective tuning of the T c value of a multilayered perovskite photoferroelectric system still remains a huge challenge. Here, by a halogen substitution strategy to introduce bromine atoms on n -propylamine cations, the hybrid perovskite photoferroelectric (3-bromopropylaminium) 2 (formamidinium)Pb 2 Br 7 ( BFPB ) with a high T c value (348.5 K) was obtained. It is notable that BFPB adopts a two-dimensional bilayered inorganic framework, with tight linking to the organic cation by C-Br···Br-Pb halogen···halogen interactions and N-H···Br hydrogen bonds. Intriguingly, in comparison with the prototypical compound ( n -propylaminium) 2 (formamidinium)Pb 2 Br 7 , a remarkable augmentation of 85.2 K in the resulting T c value of BFPB is clearly observed, which further broadens the temperature range of its application. In combination with the remarkable ferroelectric and semiconducting attributes, the reversible bulk photovoltaic effect was realized in single crystals of BFPB . This finding can not only enhance the hybrid perovskite ferroelectric family but also further promote the photoelectric application of ferroelectrics.

Ferroelectric semiconductors, combining semiconduction, spontaneous polarization, and photoinduced excitation, show great promise to enhance the performance of solar cells, pressure sensors, and photodetectors. Particularly, organic-inorganic lead halide perovskite ferroelectrics have been explored for their prominent carrier transport properties and structural tunability. However, a high concentration of toxic Pb is a stumbling block for their further application. Here, we present a lead-free hybrid perovskite semiconductor, (C 4 H 9 NH 3 ) 2 (NH 3 CH 3 ) 2 Sn 3 Br 10 ( 1 ), which exhibits a large spontaneous polarization of 11.76 μC cm -2 at room temperature. Significantly, 1 presents a spontaneous polar ordering transition, similar to the better-known perovskite ferroelectrics, and exhibits ferroelectric phase transition behaviors. To our best knowledge, 1 is the first example of a Sn-based hybrid perovskite semiconductor featuring ferroelectric performance. Mechanistic studies reveal that such ferroelectricity can be attributable to the synergistic effects of ordering of organic cations and stereochemically active lone-pair electrons inducing distortion of inorganic octahedra. This work provides an effective way to explore "green" ferroelectric semiconductors with potentially enhanced energy conversion efficiency.

Perovskite ferroelectrics, in which the spontaneous polarization ( P s ) is conducive to the separation of photoexcited charge carriers, have shown great potential for self-powered photodetection. Nevertheless, such self-powered ferroelectric photodetectors are mostly dominated by traditional inorganic oxides and exhibit relatively small zero-bias photocurrent, which limit their further application. Herein, we present a wide-bandgap 2D trilayered lead chloride hybrid perovskite ferroelectric, EA 4 Pb 3 Cl 10 ( 1 , EA = ethylammonium), which shows a notable P s of ∼4.5 μC/cm 2 and a high Curie temperature (415 K) beyond that of BaTiO 3 (393 K). Significantly, benefiting from the wide bandgap of 3.39 eV, a self-powered visible-blind ultraviolet (UV) photodetector has been successfully realized, with a zero-bias photocurrent as high as 18.6 μA/cm 2 , which is nearly 2 orders of magnitude larger than those of mostly conventional inorganic ferroelectrics. As a pioneering study, this work offers an efficient approach for exploring wide-bandgap perovskite ferroelectrics and will excavate their application in the field of self-powered visible-blind UV photodetection.

Lead-free organic-inorganic hybrid perovskites have recently attracted intense interest as environmentally friendly, low-cost, chemically stable light absorbers. Here, we reported a new one-dimensional (1D) zigzag chainlike light-absorbing hybrid material of (C 6 H 13 N) 2 BiI 5 , in which the corner-sharing octahedral bismuth halide chains are surrounded by organic cations of tetramethylpiperidinium. This unique zigzag 1D hybrid perovskite-derivative material shows a narrow direct band gap of 2.02 eV and long-lived photoluminescence, which is encouraging for optoelectronic applications. Importantly, it behaves as a typical semiconducting material and displays obvious photoresponse in the visible-light range. This work opens a potential pathway for the further application of 1D lead-free hybrids.

The incommensurate (IC) behaviors of ferroelectrics have been widely investigated in inorganic oxides as an exciting branch for aperiodic materials, whereas it still remains a great challenge to achieve such intriguing effects in organic systems. Here, we present that successive ordering of dynamic dipoles in an organic molecular ferroelectric, N-isopropylbenzylaminium trichloroacetate (1), enables unusual incommensurately modulated structures between its paraelectric phase and ferroelectric phase. In particular, 1 exhibits three distinct IC states coupling with a long-range ordering modulation. That is, the incommensurately modulated lattice is ∼7 times as large as its periodic prototype, and the IC structure is well solved using a (3 + 1)D superspace group with the modulated wavevector q = (0, 0, 0.1589). To the best of our knowledge, 1 is the first organic ferroelectric showing such a long-range ordering IC structural modulation. In addition, structural analyses reveal that slowing down dynamic motions of anionic moieties accounts for its modulation behaviors, which also results in dramatic reorientation of dipolar moments and concrete ferroelectric polarization of 1 (∼0.65 μC/cm 2 ). The combination of unique IC structural modulations and ferroelectricity makes 1 a potential candidate for the assembly of an artificially modulated lattice, which will allow for a deep understanding of the underlying chemistry and physics of aperiodic materials.

Hybrid organic-inorganic perovskite materials have demonstrated great potential in the field of photovoltaics and photoelectronics. On the basis of the high degree of structural flexibility and compatibility, diverse molecular functional materials have been assembled by modifying the length of the organic components and/or dimensionality of the inorganic frameworks. In this paper, we present a chiral lead-free organic-inorganic hybrid, (piperidinium) 2 SbCl 5 (1), which follows the one-dimensional inorganic frameworks of the corner-sharing SbCl 6 octahedra. Strikingly, 1 displays a dielectric phase transition at T c = 338 K, changing from the chiral space group of P2 1 2 1 2 1 to polar Pna2 1 upon heating. Crystal structure analyses reveal that an unusual thermally activated conformation change of the piperidinium cations affords the driving force to the phase transition of 1. That is, organic piperidinium moieties display a chairlike conformation below T c , which transforms to a boatlike structure above T c . Such an unprecedented change is strongly coupled to the dielectric transition along with notable steplike anomalies, which suggest that 1 could be used as a potential switchable dielectric material. Besides, the temperature-dependent conductivity and theoretical analysis of its electronic structure disclose the semiconducting behavior of 1. This study paves the pathway to the design of new lead-free semiconducting perovskites with targeted properties for optoelectronic application.

Organic-inorganic hybrid lead halide (e.g., CH 3 NH 3 PbX 3 , where X = CI, Br, and I) nanowires (NWs) with remarkable electric and optical properties have recently garnered increasing attention, owing to their structural flexibility and tunability compared to inorganic semiconducting NWs. While most recently reported NWs are limited to methylammonium/formamidinium three-dimensional lead halide perovskites, it is urgent to develop new organic-inorganic hybrid semiconducting NWs. Here, broad-band-emissive single-crystal semiconductive NWs based on a new ABX 3 -type organic-inorganic chain hybrid, (2-methylpiperidine)lead tribromide, are reported. It is believed that this work will enrich the organic-inorganic hybrid semiconducting NWs and may provide potential applications for LED displaying.

Perovskite-type hybrids (e.g., CH 3 NH 3 PbI 3 ) hold great promise in photovoltaics and optoelectronics due to their remarkable semiconducting properties and potential ferroelectricity. However, to date, conclusive evidence for the bulk ferroelectricity of CH 3 NH 3 PbI 3 is still lacking. In this context, it is highly desirable to assemble concrete perovskite ferroelectric hybrids with the semiconducting feature. Here we report, for the first time, a class of lead-free perovskite halides, (N-methylpyrrolidinium) 3 Sb 2 Cl 9-9x Br 9x (x = 0-1), showing large ferroelectric polarizations (5.2-7.6 μC/cm 2 ) and pronounced semiconducting performances. In particular, a wide tunability of their optical bandgaps (3.31-2.76 eV) enables superior visible-light-induced photocurrents (∼10 nA/cm 2 ), which allow for assembling of the crystal-based photodetectors. Our work paves a new way to build environmentally benign optoelectronic devices based on low-bandgap ferroelectric hybrids.

A high efficiency of laser-light conversion and short cutoff edge is essential to an ultraviolet (UV) nonlinear-optical (NLO) material. Previous researches on phosphates were mainly centered on alkali-metal or alkali-earth-metal phosphate systems, resulting in relatively weak NLO responses. Through the introduction of transition-metal cadmium and alkali-metal cesium elements with large radii into the phosphate system, a new UV NLO pyrophosphate, CsLiCdP 2 O 7 , has been synthesized. It exhibits a high second-harmonic-generation (SHG) efficiency of 1.5KH 2 PO 4 and is transparent down to 200 nm. This work provides a new path for the design of UV NLO materials with high SHG efficiencies and short cutoff edges by introducing a transition metal with a d 10 electron configuration and an alkali metal with a large radius into phosphate systems.

A new one-dimensional ABX3-type organic-inorganic hybrid phase transition compound, 1-pentyl-3-methylimidazolium tribromoplumbate (1), where the Pb(II) ion exhibits hemicoordination geometry, resulting in anionic (PbBr3)n chains of an edge-shared PbBr5 polyhedron, has been successfully synthesized. 1 undergoes a reversible second-order phase transition at about 136 K. The dielectric constants of 1 exhibit an obvious steplike anomaly tuned between a high dielectric state in the high-temperature phase and a low state in the low-temperature phase. The origin of its phase transition is ascribed to the order-disorder transformation of the cation coupled with the relative displacement of the Br atoms. These findings provide a new approach to exploring a novel ABX3-type compound with functional phase transition properties.

It is challenging to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance between deep-UV transparency and high NLO activity. Known deep-UV NLO materials are almost exclusively limited to borates, except few newly discovered phosphates despite their small NLO activities. Here we report two asymmetric phosphates, RbBa2(PO3)5 (I) and Rb2Ba3(P2O7)2 (II), which feature [PO3]∞ chains and [P2O7](4-) dimers formed by condensation of [PO4](3-) units, respectively. Remarkably, I achieves the desired balance, with the shortest deep-UV absorption edge at 163 nm and the largest NLO activity of 1.4 × KDP (KH2PO4) in deep-UV NLO phosphates. According to first-principles calculations, the enhanced macroscopic SHG response of I can be attributed to the [PO3]∞ chains which exhibit significantly larger microscopic SHG coefficients as compared with the [P2O7](4-) dimers.