Precisely Tailoring a FAPbI3-Derived Ferroelectric for Sensitive Self-Driven Broad-Spectrum Polarized Photodetection

Bulk Photovoltaic Effect in Polar 3D Perovskitoid Enables Self-Powered Polarization-Sensitive Photodetection

The family of polar hybrid perovskites, in which bulk photovoltaic effects (BPVEs) drive steady photocurrent without bias voltage, have shown promising potentials in self-powered polarization-sensitive photodetection. However, reports of BPVEs in 3D perovskites remain scare, being mainly hindered by the limited dipole moment or lack of symmetry breaking. Herein, a polar 3D perovskitoid, (BDA)Pb2Br6 (BDA = NH3C4H8NH3), where the spontaneous polarization (Ps)-induced BPVE drives self-powered photodetection of polarized-light is reported. Emphatically, the edge-sharing Pb2Br10 dimer building unit allows the optical anisotropy and polarity in 3D (BDA)Pb2Br6, which triggers distinct optical absorption dichroism ratio of ≈2.80 and BPVE dictated photocurrent of 3.5 µA cm-2. Strikingly, these merits contribute to a polarization-sensitive photodetection with a high polarization ratio (≈4) under self-powered mode, beyond those of 2D hybrid perovskites and inorganic materials. This study highlights the potential of polar 3D perovskitoids toward intelligent optoelectronic applications.

Dual polarization-enabled ultrafast bulk photovoltaic response in van der Waals heterostructures

The bulk photovoltaic effect (BPVE) originating from spontaneous charge polarizations can reach high conversion efficiency exceeding the Shockley-Queisser limit. Emerging van der Waals (vdW) heterostructures provide the ideal platform for BPVE due to interfacial interactions naturally breaking the crystal symmetries of the individual constituents and thus inducing charge polarizations. Here, we show an approach to obtain ultrafast BPVE by taking advantage of dual interfacial polarizations in vdW heterostructures. While the in-plane polarization gives rise to the BPVE in the overlayer, the charge carrier transfer assisted by the out-of-plane polarization further accelerates the interlayer electronic transport and enhances the BPVE. We illustrate the concept in MoS2/black phosphorus heterostructures, where the experimentally observed intrinsic BPVE response time achieves 26 ps, orders of magnitude faster than that of conventional non-centrosymmetric materials. Moreover, the heterostructure device possesses an extrinsic response time of approximately 2.2 ns and a bulk photovoltaic coefficient of 0.6 V-1, which is among the highest values for vdW BPV devices reported so far. Our study thus points to an effective way of designing ultrafast BPVE for high-speed photodetection.

Realization of High-Performance Self-Powered Polarized Photodetection with Large Temperature Window in a 2D Polar Perovskite

Polarization photodetection taking advantage of the anisotropy of 2D materials shines brilliantly in optoelectronic fields owing to differentiating optical information. However, the previously reported polarization detections are mostly dependent on external power sources, which is not conducive to device integration and energy conservation. Herein, a 2D polar perovskite (CBA)2CsPb2Br7 (CCPB, CBA = 4-chlorobenzyllamine) has been successfully synthesized, which shows anticipated bulk photovoltaic effect (BPVE) with an open-circuited photovoltage up to ≈0.2 V. Devices based on CCPB monomorph fulfill a fascinating self-powered polarized photodetection with a large polarization ratio of 2.7 at room temperature. Moreover, CCPB features a high phase-transition temperature (≈475 K) which prompts such self-powered polarized photodetection in a large temperature window of device operation, since BPVE generated by spontaneous polarization can only exist in the polar structure prior to the phase transition. Further computational investigation reveals the introduction of CBA+ with a large dipole moment contributes to quite large polarization (17.5 µC cm-2) and further super high phase transition temperature of CCPB. This study will promote the application of 2D perovskite materials for self-powered polarized photodetection in high-temperature conditions.

Bulk Photovoltaic Effect Induced by Non-Covalent Interactions in Bilayered Hybrid Perovskite for Efficient Passive X-Ray Detection

Hydrogen bonding as a multifunctional tool has always influenced the structure of hybrid perovskites. Compared with the research on hydrogen bonding, the study of halogen-halogen interactions on the structure and properties of hybrid perovskites is still in its early stages. Herein, a polar bilayered hybrid perovskite (IEA)2FAPb2I7 (IEA+ is 2-iodoethyl-1-ammonium, FA is formamidinium) with iodine-substituted spacer is successfully constructed by changing the configuration of interlayer cations and regulating non-covalent interactions at the organic-inorganic interface, which shows a shorter interlayer spacing and higher density (ρ = 3.862 g cm-3). The generation of structure polarity in (IEA)2FAPb2I7 is caused by the synergistic effect of hydrogen bonding and halogen-halogen interactions. Especially, as the length of the carbon chain in organic cations decreases, the I---I interaction in the system gradually strengthens, which may be the main reason for the symmetry-breaking. Polarity-induced bulk photovoltaics (Voc = 1.0 V) and higher density endow the device based on (I-EA)2FAPb2I7 exhibit a high sensitivity of 175.6 µC Gy-1 cm-2 and an ultralow detection limit of 60.4 nGy s-1 at 0 V bias under X-ray irradiation. The results present a facile approach for designing polar multifunctional hybrid perovskites, also providing useful assistance for future research on halogen-halogen interactions.

Intercorrelated Ferroelectricity and Bulk Photovoltaic Effect in Two-Dimensional Sn2P2S6 Semiconductor for Polarization-Sensitive Photodetection

A two-dimensional (2D) ferroelectric semiconductor, which is coupled with photosensitivity and room-temperature ferroelectricity, provides the possibility of coordinated conductance modulation by both electric field and light illumination and is promising for triggering the revolution of optoelectronics for monolithic multifunctional integration. Here, we report that semiconducting Sn2P2S6 crystals can be achieved in a 2D morphology using a chemical vapor transport approach with the assistant of space confinement and experimentally demonstrate the robust ferroelectricity in atomic-thin Sn2P2S6 nanosheet at room temperature. The intercorrelated programming of ferroelectric order along out-of-plane (OOP) and in-plane (IP) directions enables a tunable bulk photovoltaic (BPV) effect through multidirectional electrical control. By combining the capability of anisotropic in-plane optical absorption, a highly integrated Sn2P2S6 optoelectronic device vertically sandwiched with graphene electrodes yields the polarization-dependent open-circuit photovoltage with a dichroic ratio of 2.0 under 405 nm light illumination. The reintroduction of ferroelectric Sn2P2S6 to the 2D asymmetric semiconductor family provides possibilities to hardware implement of the self-powered polarization-sensitive photodetection and spotlights the promising applications for next-generation photovoltaic devices.

Phase Transitions and Dynamics in Mixed Three- and Low-Dimensional Lead Halide Perovskites

Lead halide perovskites are extensively investigated as efficient solution-processable materials for photovoltaic applications. The greatest stability and performance of these compounds are achieved by mixing different ions at all three sites of the APbX3 structure. Despite the extensive use of mixed lead halide perovskites in photovoltaic devices, a detailed and systematic understanding of the mixing-induced effects on the structural and dynamic aspects of these materials is still lacking. The goal of this review is to summarize the current state of knowledge on mixing effects on the structural phase transitions, crystal symmetry, cation and lattice dynamics, and phase diagrams of three- and low-dimensional lead halide perovskites. This review analyzes different mixing recipes and ingredients providing a comprehensive picture of mixing effects and their relation to the attractive properties of these materials.

Chiral-Achiral Cations Intercalation Induced Lead-Free Chiral-Polar Hybrid Perovskites Enable Self-Powered X-Ray and Ultraviolet-Visible-Near-Infrared Photo Detection

Lead halide hybrid perovskites have made great progress in direct X-ray detection and broadband photodetection, but the existence of toxic Pb and the demand for external operating voltage have severely limited their further applications and operational stability improvements. Therefore, exploring "green" lead-free hybrid perovskite that can both achieve X-ray detection and broadband photodetection without external voltage is of great importance, but remains severely challenging. Herein, using centrosymmetric (BZA)3BiI6 (1, BZA = benzylamine) as a template, a pair of chiral-polar lead-free perovskites, (BZA)2(R/S-PPA)BiI6 (2-R/S, R/S-PPA = (R/S)-1-Phenylpropylamine) are successfully obtained by introducing chiral aryl cations of (R/S)-1-Phenylpropylamine. Compared to 1, chiral-polar 2-R presents a significant irradiation-responsive bulk photovoltaic effect (BPVE) with an open circuit photovoltage of 0.4 V, which enables it with self-powered X-ray, UV-vis-NIR broadband photodetection. Specifically, 2-R device exhibits an ultralow detection limit of 18.5 nGy s-1 and excellent operational stability. Furthermore, 2-R as the first lead-free perovskite achieves significant broad-spectrum (377-940 nm) photodetection via light-induced pyroelectric effect. This work sheds light on the rational crystal reconstruction engineering and design of "green" hybrid perovskite toward high-demanded self-powered radiation detection and broadband photodetection.

Nonlinear Optical Switching in a Tin-Based Multilayered Halide Perovskite Activated by Stereoactive Lone Pairs and Confined Rotators

In recent years, there has been a surge in research enthusiasm on searching for solid-state nonlinear optical (NLO) switching materials in halide perovskites owing to their exceptional structural flexibility, compositional diversity, and broad property tenability. However, the majority of reported halide perovskite NLO switching materials contain toxic elements (e.g., Pb), which raise significant environmental concerns. Herein, we present a novel lead-free multilayered halide perovskite NLO switching material, (BA)2(EA)2Sn3Br10 (1, where BA is butylammonium and EA is ethylammonium). Driven by the stereochemically active lone-pair electrons of the Sn2+ cation and the cage-confined effect of EA rotators, 1 undergoes a phase transition with symmetry breaking from P4/mnc to Cmc21, which gives rise to a highly efficient modulation of the quadratic NLO property (0.7 times that of KH2PO4) at a high temperature of 353 K. Furthermore, crystallographic investigation combined with theoretical calculations reveals that the efficient modulation of NLO properties in 1 stems from the synergistic effects between stereochemically active lone pair-induced octahedral distortions and order/disorder transformation of organic cations. This study opens up an instructive avenue for designing and advancing environmentally friendly solid-state NLO switches in halide perovskites.

X-ray-Induced Pyroelectric Effect in a Perovskite Ferroelectric Drives Low Detection Limit Self-Powered Responses

The light-induced pyroelectric effect (LPE) has shown a great promise in the application of optoelectronic devices, especially for self-powered detection and imaging. However, it is quite challenging and scarce to achieve LPE in the X-ray region. For the first time, we report X-ray LPE in a single-phase ferroelectric of (NPA)2(EA)2Pb3Br10 (1, NPA = neopentylamine, EA = ethylamine), adopting a two-dimensional trilayered perovskite motif, which has a large spontaneous polarization of ∼3.7 μC/cm2. Its ferroelectricity allows for significant LPE in the wavelength range of ordinary visible light. Strikingly, the X-ray LPE is observed in 1, which endows remarkable self-powered X-ray responses at 0 bias, including sensitivity up to 225 μC Gy-1 cm-2 and a low detection limit of ∼83.4 nGy s-1, being almost 66 times lower than the requirement for medical diagnostics (∼5.5 μGy s-1). This work not only develops a new mode for X-ray detection but also provides valuable insights for future photoelectric device application.

Pioneering Two-Dimensional Perovskites Featuring Four-Layer Organic Spacers for Polarization-Sensitive Photodetection

Hybrid perovskites have great potential in photovoltaics and photodetection. Specially, two-dimensional (2D) hybrid perovskites have been discovered to show distinctive applications in polarization-sensitive photodetection due to their intrinsic anisotropy. Herein, we designed a new type of 2D perovskite by introducing bifunctional alkylammonium as an organic spacer, (β-Ala)4PbBr4 (1, where β-Ala+ is 3-aminopropanoic), which has four organic spacers in adjacent inorganic layers and adjacent organic layers are linked by hydrogen bonding. The pioneering structure with four organic spacers enables an intrinsic high strong anisotropy, facilitating polarization-sensitive detection. The analysis of the crystal structure and optical properties further elucidates the natural anisotropic properties of 1. Strikingly, 1 has a strong optical dichroism (αc/αb ≈ 7.4 in 405 nm), and the polarization-sensitive detector on single crystals of 1 exhibits a large polarization ratio (Imax/Imin ≈ 2.0). This result highlights that the employment of bifunctional cations is efficient to explore new type 2D perovskites for potentially high-performance polarization-sensitive detection.

Radiation Photovoltaics in a 2D Multilayered Chiral-Polar Halide Perovskite toward Efficient Self-Driven X-Ray Detection

2D multilayered organic-inorganic hybrid perovskites (OIHPs) have exhibited bright prospects for high-performance self-driven X-ray detection due to their strong radiation absorption and long carrier transport. However, as an effective tool for self-driven X-ray detection, radiation photovoltaics remain rare, and underdeveloped in multilayered OIHPs. Herein, chirality to induce radiation photovoltaics in 2D multilayered chiral OIHPs is first utilized for efficient self-driven X-ray detection. Specifically, under X-ray irradiation, a multilayered chiral-polar (S-BPEA)2 FAPb2 I7 (1-S, S-BPEA = (S)-1-4-Bromophenylethylammonium, FA = formamidinium) shows remarkable radiation photovoltaics of 0.85 V, which endows 1-S excellent self-driven X-ray detection performance with a considerable sensitivity of 87.8 µC Gyair -1  cm-2 and a detection limit low to 161 nGyair  s-1 . Moreover, the sensitivity is high up to 1985.9 µC Gyair -1  cm-2 under 80 V bias, higher than most those of 2D OIHPs. These results demonstrate that chirality-induced radiation photovoltaics is an efficient strategy for self-driven X-ray detection.

Pyro-Phototronic Effect in All-Inorganic Two-Dimensional Ruddlesden-Popper Ferroelectric Perovskite Thin-films and Photodetection

Ferroelectric perovskites, where ferroelectricity is embedded in the structure, are being considered for different device applications. In this study, we introduce Cs2PbI2Cl2, an all-inorganic 2D Ruddlesden-Popper (RP) halide perovskite, as a ferroelectric material suitable for pyro-phototronic applications. Thin-films of the all-inorganic perovskite are successfully cast, and they demonstrate ferroelectric properties. Unlike hybrid materials, the ferroelectricity in Cs2PbI2Cl2 does not rely on the organic moiety possessing an electric dipole moment. Instead, the 2D-layer-forming octahedra are twisted and tilted due to a distortion in the bond lengths, leading to the emergence of spontaneous electric polarization. Based on the properties, we fabricate p-i-n heterojunctions by integrating the perovskite with carrier-transport layers. To determine the band-energies of the materials, scanning tunneling spectroscopy and Kelvin probe force microscopy are employed. The band-edges evidence a type-II band-alignment at both interfaces, enabling the material to exhibit both photovoltaic and pyroelectric behaviors when subjected to pulsed illumination. The devices based on the all-inorganic RP perovskite developed in this study exhibit pyro-phototronic effects and serve as self-powered photodetectors without any need for an external bias.

Quantum tailoring for polarization-discriminating Bi2S3 nanowire photodetectors and their multiplexing optical communication and imaging applications

In this study, cost-efficient atmospheric pressure chemical vapor deposition has been successfully developed to produce well-aligned high-quality monocrystalline Bi2S3 nanowires. By virtue of surface strain-induced energy band reconstruction, the Bi2S3 photodetectors demonstrate a broadband photoresponse across 370.6 to 1310 nm. Upon a gate voltage of 30 V, the responsivity, external quantum efficiency, and detectivity reach 23 760 A W-1, 5.55 × 106%, and 3.68 × 1013 Jones, respectively. The outstanding photosensitivity is ascribed to the high-efficiency spacial separation of photocarriers, enabled by synergy of the axial built-in electric field and type-II band alignment, as well as the pronounced photogating effect. Moreover, a polarization-discriminating photoresponse has been unveiled. For the first time, the correlation between quantum confinement and dichroic ratio is systematically explored. The optoelectronic dichroism is established to be negatively correlated with the cross dimension (i.e., width and height) of the channel. Specifically, upon 405 nm illumination, the optimized dichroic ratio reaches 2.4, the highest value among the reported Bi2S3 photodetectors. In the end, proof-of-concept multiplexing optical communications and broadband lensless polarimetric imaging have been implemented by exploiting the Bi2S3 nanowire photodetectors as light-sensing functional units. This study develops a quantum tailoring strategy for tailoring the polarization properties of (quasi-)1D material photodetectors whilst depicting new horizons for the next-generation opto-electronics industry.

Introducing Ferroelasticity into 1D Hybrid Lead Halide Semiconductor by Halogen Substitution Strategy

Organic-inorganic hybrid lead halide perovskites (OLHPs), represented by (CH3 NH3 )PbI3 , are one of the research focus due to their exceptional performance in optoelectronic applications, and ferroelastic domain walls are benign to their charge carrier transport that is confirmed recently. Among them, the 1D OLHPs feature better stability against desorption and moisture, but related 1D ones possessing ferroelasticity are rarely investigated and reported so far. In this work, the 1D ferroelastic semiconductor (N-iodomethyl-N-methyl-morpholinium)PbI3 ((IDMML)PbI3 ) is prepared successfully by introducing successively halogenate atoms from Cl, Br to I into the organic cation of the prototype (N,N-dimethylmorpholinium)PbI3 ((DMML)PbI3 ). Notably, (IDMML)PbI3 shows the narrow bandgap energy (≈2.34 eV) according to the ultraviolet-visible absorption spectrum and the theoretical calculation, and possesses the evident photoconductive characteristic with the on/off ratio of current of ≈50 under the 405 nm light irradiation. This work provides a new case for the ferroelastic OLHPs and will inspire intriguing research in the field of optoelectronic.

Giant Polarization Sensitivity via the Anomalous Photovoltaic Effect in a Two-Dimensional Perovskite Ferroelectric

Polarization sensitivity, which shows great potential in photoelectric detection, is expected to be significantly improved by the ferroelectric anomalous photovoltaic (APV) effect. However, it is challenging to explore new APV-active ferroelectrics due to severe polarization fatigue induced by the leakage current of photoexcited carriers. For the first time, we report a strong APV effect in a 2D hybrid perovskite ferroelectric assembled by alloying mixed organic cations, (HA)₂(EA)₂Pb₃Br₁₀ (1, where HA⁺ is n-hexylammonium and EA⁺ is ethylammonium), which has a large spontaneous polarization ∼3.8 μC/cm² and high a Curie temperature ∼378 K. Its ferroelectricity allows a strong APV effect with an above-bandgap photovoltage up to 7.4 V, which exceeds its bandgap (∼2.7 eV). Most strikingly, based on the dependence on polarized-light angle, this strong APV effect renders the highest level of polarization sensitivity with a giant current ratio of ∼25, far beyond other 2D single-phase materials. This study sheds light on the exploration of APV-active ferroelectrics and inspires their future high-performance optoelectronic device applications.

Second harmonic generation from symmetry breaking stimulated by mixed organic cations in zero-dimensional hybrid metal halides

Mixing cations with different chemical properties to induce the generation of asymmetric structures is a new approach for tuning the optical properties of hybrid organic-inorganic metal halides (HOIMHs). In this study, zero-dimensional (C₉N₃H₁₅)(C₉H₁₃SO)MBr₆ (M = Bi/Sb, [C₉N₃H₁₅]²⁺ = [(C₄N₂H₁₀)(C₅NH₅)]²⁺ and [C₉H₁₄SO]⁺ = [CH₃(C₆H₄)OS(CH₃)₂]⁺) are synthesized. Two different cations cause both compounds to crystallize in the polar space group P2₁2₁2₁, thus resulting in significant phase matchable second harmonic generation under a 1064 nm laser excitation. Thus, (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit intensities that are approximately 1.8 and 1.7 times that of KH₂PO₄, respectively. The results of density functional theory calculations show that both (C₉N₃H₁₅)(C₉H₁₃SO)BiBr₆ and (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibit direct bandgaps of 2.95 and 2.81 eV, respectively. Additionally, because of the distortion of the inorganic octahedra, (C₉N₃H₁₅)(C₉H₁₃SO)SbBr₆ exhibited bright yellow emission at room temperature, which is attributed to ns² fluorescence emission. We believe that the symmetry of the HOIMH crystal structure can be broken by introducing spatially differentiated bifunctional organic cations, which consequently enables even-order nonlinear activities.

Stepwise Solution-Interfacial Nanoarchitectonics for Assembled Film with Full-Color and White-Light Circularly Polarized Luminescence

The fabrication of chiral thin films with tunable circularly polarized luminescence (CPL) colors is important in developing chiroptical materials but remains challenging due to the lack of assembly-initiated chiral film formation methodology. Here, by adopting a combined solution aggregation and interfacial assembly strategy, we report the fabrication of chiral film materials with full-color and white-light CPL. A biquinoline glutamic acid ester (abbreviated as BQGE) shows a typical aggregation-induced emission property with blue CPL after solution aggregation. Subsequent interfacial assembly of these solution aggregates on a solid substrate leads to the formation of a CPL active film consisting of nanobelt structures. Since the BQGE molecule has a coordination site, the CPL emission of an individual BQGE film can be extended from blue to green emission upon coordination with a zinc ion, accompanied by morphology transition from nanobelts to nanofibers. Further extension to red-color CPL is successfully achieved by coassembly with an achiral acceptor dye. Interestingly, the proper combination of coordination ratio and acceptor loading ratio provides bright white-light CPL emission from the BQGE/Zn²⁺/PDA triad composite film. This work provides a new approach to fabricating chiroptical film materials with controlled microscopic morphology and tunable CPL properties.