Tailoring the Time-Averaged Structure for Polarization-Sensitive Chiral Perovskites

Spin detector for panchromatic circularly polarized light detection

Circularly polarized light (CPL) detection is crucial for optical communication, bioimaging and quantum computing. However, CPL detectors based on chiral low-dimensional perovskites face a trade-off between optoelectronic performance and CPL discrimination, and typically exhibit a CPL response within a narrow spectral range. Here, we overcome these limitations by integrating three-dimensional (3D) and chiral-two-dimensional (2D) perovskites. The 3D perovskite serving as the photoabsorption layer extends the detection range to 760 nm and enhances optoelectronic responses, while also generating spin-polarized carriers through large Rashba splitting. The chiral-2D perovskite achieves spin filtering efficiency up to 80%. The synergy between spin polarization and chiral-induced spin selectivity processes enables a panchromatic CPL response, with a photocurrent asymmetry factor exceeding 0.28 across the visible spectrum and peaking at 0.35. Furthermore, our detector achieves a detectivity of 3.7×1011 Jones. Our work introduces a spin manipulation strategy for panchromatic CPL detection, expanding the scope of spintronics applications.

Two 3D Rare-Earth Double Perovskite Materials Constructed with a Pair of Enantiomers

Organic-inorganic hybrid chiral small-molecule materials combine the inherent properties of both components; however, studies integrating chirality with rare-earth double-perovskite materials are limited. In this work, we synthesized two enantiomers of three-dimensional (3D) hybrid rare-earth double-perovskites, [R-3-HDMP]2CsEu(NO3)6 (1) and [S-3-HDMP]2CsEu(NO3)6 (2), by reacting R-3-HDMP and S-3-HDMP (where 3-HDMP = 3-hydroxy-N,N-dimethylpyrrole) with CsNO3 and Eu(NO3)3 in a 2:1:1 ratio within an acidic solution. Both R-3-HDMPI and S-3-HDMPI crystallize in the chiral space group P212121 at room temperature, exhibiting a transition from SHG-on to SHG-off (SHG = second harmonic generation) upon heating and cooling. The temperature-dependent X-ray single-crystal diffraction analysis carried out on compound 1 and compound 2, before and after the phase transition, disclosed the transformation of their space groups from noncentrosymmetric to centrosymmetric. Additionally, the incorporation of rare-earth elements as hybrid B-site cations imparts exceptional fluorescence properties to the compounds. These materials effectively merge the unique characteristics of chiral molecules with the exceptional luminescence of double-perovskite structures, paving the way for innovative optical devices and advanced information processing technologies.

Atomistic Origin of Microsecond Carrier Lifetimes at Perovskite Grain Boundaries: Machine Learning-Assisted Nonadiabatic Molecular Dynamics

The polycrystalline nature of perovskites, stemming from their facile solution-based fabrication, leads to a high density of grain boundaries (GBs) and point defects. However, the impact of GBs on perovskite performance remains uncertain, with contradictory statements found in the literature. We developed a machine learning force field, sampled GB structures on a nanosecond time scale, and performed nonadiabatic (NA) molecular dynamics simulations of charge carrier trapping and recombination in stoichiometric and doped GBs. The simulations reveal long, microsecond carrier lifetimes, approaching experimental data, stemming from charge separation at the GBs and small NA coupling, 0.01-0.1 meV. Stoichiometric GBs exhibit transient trap states, which, however, are not particularly detrimental to the carrier lifetime. Halide dopants form interstitial defects in the bulk, but have a stabilizing influence on the GB structure by passivating undersaturated Pb atoms and reducing the transient trap state formation. On the contrary, excess Pb destabilizes GBs, allowing formation of persistent midgap states that trap charges. Still, the charge carrier lifetime reduces relatively little, because the midgap states decouple from the bands, and charges are more likely to escape back into bands upon a GB structural fluctuation. The atomistic study into the structural dynamics of perovskite GBs and its influence on charge carrier trapping and recombination provides valuable insights into the complex properties of perovskites and the intricate role of GBs in the material performance.

Nucleation-Controlled Crystallization of Chiral 2D Perovskite Single Crystal Thin Films for High-Sensitivity Circularly Polarized Light Detection

2D Dion-Jacobson (DJ) chiral perovskite materials exhibit significant promise for developing high-performance circularly polarized light (CPL) photodetectors. However, the inherently thick nature of DJ-phase 2D perovskite single crystal limits their ability to differentiate CPL photons with the two opposite polarization states. In addition, the growth of DJ-phase perovskite single crystal thin films (SCTFs) has proven challenging due to the strong interlayer electronic coupling. Here, a nucleation-controlled strategy is employed to grow a novel DJ-phase perovskite [(R/S)-3APr]PbI4 [(R/S)-3APr = (R/S)-3-Aminopyrrolidine] SCTFs with large area, low thickness and hence high aspect ratios. Structural and photoluminescence analyses reveal that introducing the divalent organic cations into the perovskite framework reduce the interlayer distance, resulting in low exciton binding energy. This facilitates charge separation and transport. The resulting SCTF photodetector showcases excellent detection performance with anisotropy factor for photocurrent as high as 0.65, responsivity of 1.97 A W-1, detectivity of 5.3 × 1013 Jones, and 3-dB frequency of 2940 Hz, demonstrating its potential as a promising candidate for CPL-sensitive photodetectors. This novel approach, therefore, provides a framework for the growth of DJ-phase perovskite SCTFs and advances their applications in sensitive CPL photodetection.

Chiroptical Synaptic Perovskite Memristor as Reconfigurable Physical Unclonable Functions

Physical unclonable functions (PUFs), often referred to as digital fingerprints, are emerging as critical elements in enhancing hardware security and encryption. While significant progress has been made in developing optical and memory-based PUFs, integrating reconfigurability with sensitivity to circularly polarized light (CPL) remains largely unexplored. Here, we present a chiroptical synaptic memristor (CSM) as a reconfigurable PUF, leveraging a two-dimensional organic-inorganic halide chiral perovskite. The device combines CPL sensitivity with photoresponsive electrical behavior, enabling its application in optoneuromorphic systems, as demonstrated by its ability to perform image categorization tasks within neuromorphic computing. Furthermore, by leveraging a 10 × 10 crossbar array of the CSMs, we develop a PUF capable of generating reconfigurable cryptographic keys based on the combination of neuromorphic potentiation and polarized light conditions. This work demonstrates an integrated approach to optoneuromorphic functionality, data storage, and encryption, providing an alternative approach for reconfigurable memristor-based PUFs.

A chemical perspective on the chiral induced spin selectivity effect

This review discusses opportunities in chemistry that are enabled by the chiral induced spin selectivity (CISS) effect. First, the review begins with a brief overview of the seminal studies on CISS. Next, we discuss different chiral material systems whose properties can be tailored through chemical means, with a special emphasis on hybrid organic-inorganic layered materials that exhibit some of the largest spin filtering properties to date. Then, we discuss the promise of CISS for chemical reactions and enantioseparation before concluding.

Giant chiral amplification of chiral 2D perovskites via dynamic crystal reconstruction

Chiral hybrid perovskites show promise for advanced spin-resolved optoelectronics due to their excellent polarization-sensitive properties. However, chiral perovskites developed to date rely solely on the interaction between chiral organic ligand cations exhibiting point chirality and an inorganic framework, leading to a poorly ordered short-range chiral system. Here, we report a powerful method to overcome this limitation using dynamic long-range organization of chiral perovskites guided by the incorporation of chiral dopants, which induces strong interactions between chiral dopants and chiral cations. The additional interplay of chiral cations with chiral dopants reorganizes the morphological and crystallographic properties of chiral perovskites, notably enhancing the asymmetric behavior of chiral 2D perovskites by more than 10-fold, along with the highest dissymmetry factor of photocurrent (gPh) of ~1.16 reported to date. Our findings present a pioneering approach to efficiently amplify the chiroptical response in chiral perovskites, opening avenues for exploring their potential in cutting-edge optoelectronic applications.

Strain-Amplified Exciton Chirality in Organic-Inorganic Hybrid Materials

Chiral organic-inorganic hybrids combining chirality of organic molecules and semiconducting properties of inorganic frameworks generate chiral excitons without external spin injection, creating the potential for chiroptoelectronics. However, the relationship between molecular chirality and exciton chirality is still unclear. Here we show the strain-amplified exciton chirality in one-dimensional chiral metal halides. Utilizing chirality-induced spin-orbital coupling theory, we quantitatively demonstrate the impact of the strain-engineered molecular assembly of chiral cations on exciton chirality, offering a feasible way to amplify exciton chirality by molecular manipulation.

Coupled Kite-to-Square Distortion Transition and Physical Properties in 2D Lead Halide Perovskite

2D lead halide perovskites showcase diverse electrical and optoelectrical properties due to their adaptable structural distortion, which dictates the symmetry characteristics of the material. To accommodate the geometric shape of the cation, the inorganic layer of the 2D perovskite often undergoes specific distortions such as lead-halide bond length elongation/compression and lead atom displacement. The resultant distortion manifests as a quadrilateral shape formed by Pb atoms from four adjacent four octahedrons. The degree of distortion increases as the quadrilateral deviates further from a square shape and vice versa. This quadrilateral shape not only visually represents the magnitude of distortion but also confirms its direction. During the transition from kite to square distortion under external stimuli, the positions of the Pb atoms vividly illustrate the symmetry-breaking process, corresponding to a shift from high to low symmetry states. The electrical and optoelectronic properties, including ferroelectricity, pyroelectricity, piezoelectricity, nonlinear optical properties, and characteristics related to bulky photovoltaic effects, some of them exhibit direction dependence nature. This perspective employed a visible structural distortion approach to elucidate symmetry breaking and coupling distortion transitions with eight optoelectronic physical properties in 2D layered perovskite. We review recent research advancements and outline current challenges that help us to understand the structure-property relationship of 2D perovskite.

Self-Powered Circularly Polarized Light Detection Enabled by Chiral Two-Dimensional Perovskites with Mixed Chiral-Achiral Organic Cations

Direct detection of circularly polarized light (CPL) holds great promise for the development of various optical technologies. Chiral 2D organic-inorganic halide perovskites make it possible to fabricate CPL-sensitive photodetectors. However, selectively detecting left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light remains a significant challenge. Herein, we demonstrate a greatly enhanced distinguishability of photodiode-type CPL photodetectors based on chiral 2D perovskites with mixed chiral aryl (R)-(+),(S)-(-)-α-methylbenzylammonium (R,S-MBA) and achiral alkyl n-butylammonium (nBA) cations. The (R,S-MBA0.5nBA0.5)2PbI4 perovskites exhibit a 10-fold increase in circular dichroism signals compared to (R,S-MBA)2PbI4 perovskites. The CPL photodetectors based on the mixed-cation perovskites exhibit self-powered capabilities with a specific detectivity of 2.45 × 1012 Jones at a 0 V bias. Notably, these devices show high distinguishability (gres) factors of -0.58 and +0.54 based on (R,S-MBA0.5nBA0.5)2PbI4 perovskites, respectively, surpassing the performance of (R-MBA)2PbI4-based devices by over 3-fold and setting a record for CPL detectors based on chiral 2D n = 1 perovskites.

A dual spin-controlled chiral two-/three-dimensional perovskite artificial leaf for efficient overall photoelectrochemical water splitting

The oxygen evolution reaction, which involves high overpotential and slow charge-transport kinetics, plays a critical role in determining the efficiency of solar-driven water splitting. The chiral-induced spin selectivity phenomenon has been utilized to reduce by-product production and hinder charge recombination. To fully exploit the spin polarization effect, we herein propose a dual spin-controlled perovskite photoelectrode. The three-dimensional (3D) perovskite serves as a light absorber while the two-dimensional (2D) chiral perovskite functions as a spin polarizer to align the spin states of charge carriers. Compared to other investigated chiral organic cations, R-/S-naphthyl ethylamine enable strong spin-orbital coupling due to strengthened π-π stacking interactions. The resulting naphthyl ethylamine-based chiral 2D/3D perovskite photoelectrodes achieved a high spin polarizability of 75%. Moreover, spin relaxation was prevented by employing a chiral spin-selective L-NiFeOOH catalyst, which enables the secondary spin alignment to promote the generation of triplet oxygen. This dual spin-controlled 2D/3D perovskite photoanode achieves a 13.17% of applied-bias photon-to-current efficiency. Here, after connecting the perovskite photocathode with L-NiFeOOH/S-naphthyl ethylamine 2D/3D photoanode in series, the resulting co-planar water-splitting device exhibited a solar-to-hydrogen efficiency of 12.55%.

Structure-Guided Approaches for Enhanced Spin-Splitting in Chiral Perovskite

Hybrid organic-inorganic perovskites with diverse lattice structures and chemical composition provide an ideal material platform for novel functionalization, including chirality transfer. Chiral perovskites combine organic and inorganic sublattices, therefore encoding the structural asymmetry into the electronic structures and giving rise to the spin-splitting effect. From a structural chemistry perspective, the magnitude of the spin-splitting effect crucially depends on the noncovalent and electrostatic interaction within the chiral perovskite, which induces the local site and long-range bulk inversion symmetry breaking. In this regard, we systematically retrospect the structure-property relationships in chiral perovskite. Insight into the rational design of chiral perovskites based on molecular configuration, dimensionality, and chemical composition along with their effects on spin-splitting manifestation is presented. Lastly, challenges in purposeful material design and further integration into chiral perovskite-based spintronic devices are outlined. With an understanding of fundamental chemistry and physics, we believe that this Perspective will propel the application of multifunctional spintronic devices.

Perovskite-Supramolecular Co-Assembly for Chiral Optoelectronics

Hybrid inorganic-organic perovskites with chiral response and outstanding optoelectronic characteristics are promising materials for next-generation spin-optoelectronics. In particular, two-dimensional (2D) perovskites are promising chiroptical candidates due to their unique ability to incorporate chiral organic cations into their crystal structure, which imparts chirality. To enable their practical applications in chiral optoelectronic devices, it is essential to achieve an anisotropy factor (gCD ∼ 2) in chiral 2D perovskites. Currently, chiral 2D perovskites exhibit a relatively low gCD of 3.1 × 10-3. Several approaches have been explored to improve the chiral response of chiral 2D perovskites, including tailoring the molecular structure of chiral cations and increasing the degree of octahedral tilting in the perovskite lattice. However, current methods for chiral amplification have only achieved a moderate enhancement of gCD by 2-fold and are often accompanied by undesirable shifts or inversion in the circular dichroism spectra. There is a need for a more efficient approach to enhancing the chirality in 2D perovskites. Here, we report an innovative coassembly process that allows us to seamlessly grow chiral 2D perovskites on supramolecular helical structures. We discover that the interactions between perovskites and chiral supramolecular structures promote crystal lattice distortion in perovskites, which improves the chirality of 2D perovskites. Additionally, the obtained hierarchical coassembly can effectively harness the structural chirality of the supramolecular helices. The multilevel chiral enhancement leads to an enhancement in gCD by 2.7-fold without compromising the circular dichroism spectra of 2D perovskites.

Chiral Induced Spin Selectivity

Since the initial landmark study on the chiral induced spin selectivity (CISS) effect in 1999, considerable experimental and theoretical efforts have been made to understand the physical underpinnings and mechanistic features of this interesting phenomenon. As first formulated, the CISS effect refers to the innate ability of chiral materials to act as spin filters for electron transport; however, more recent experiments demonstrate that displacement currents arising from charge polarization of chiral molecules lead to spin polarization without the need for net charge flow. With its identification of a fundamental connection between chiral symmetry and electron spin in molecules and materials, CISS promises profound and ubiquitous implications for existing technologies and new approaches to answering age old questions, such as the homochiral nature of life. This review begins with a discussion of the different methods for measuring CISS and then provides a comprehensive overview of molecules and materials known to exhibit CISS-based phenomena before proceeding to identify structure-property relations and to delineate the leading theoretical models for the CISS effect. Next, it identifies some implications of CISS in physics, chemistry, and biology. The discussion ends with a critical assessment of the CISS field and some comments on its future outlook.

Chiral Hybrid Germanium(II) Halide with Strong Nonlinear Chiroptical Properties

Due to the pronounced anisotropic response to circularly polarized light, chiral hybrid organic-inorganic metal halides have been regarded as promising candidates for the application in nonlinear chiroptics, especially for the second-harmonic generation circular dichroism (SHG-CD) effect. However, designing novel lead-free chiral hybrid metal halides with large anisotropy factors and high laser-induced damage thresholds (LDT) of SHG-CD remains challenging. Herein, we develop the first chiral hybrid germanium halide, (R/S-NEA)3 Ge2 I7 ⋅H2 O (R/S-NGI), and systematically investigated its linear and nonlinear chiroptical properties. S-NGI and R-NGI exhibit large anisotropy factors (gSHG-CD ) of 0.45 and 0.48, respectively, along with a high LDT of 38.46 GW/cm2 ; these anisotropy factors were the highest values among the reported lead-free chiral hybrid metal halides. Moreover, the effective second-order nonlinear optical coefficient of S-NGI could reach up to 0.86 pm/V, which was 2.9 times higher than that of commercial Y-cut quartz. Our findings facilitate a new avenue toward lead-free chiral hybrid metal halides, and their implementation in nonlinear chiroptical applications.

Chirality-Induced Spin Selectivity of Chiral 2D Perovskite Enabling Efficient Spin-Dependent Oxygen Evolution Reaction

The sluggish and complex multi-step oxygen evolution reaction remains an obstacle to bias-free photoelectrochemical water-splitting systems. Several theoretical studies have suggested that spin-aligned intermediate radicals can significantly enhance the kinetic rates for oxygen generation. Herein, it is reported that the chirality-induced spin selectivity phenomena can become an impressive approach by adopting chiral 2D organic-inorganic hybrid perovskites as a spin-filtering layer on the photoanode. This chiral 2D perovskite-based water-splitting device achieves enhanced oxygen evolution performance with a reduced overpotential of 0.14 V, high fill factor, and 230% increased photocurrent compared to a device without a spin-filtering layer. Moreover, combined with a superhydrophobic patterning strategy, this device realizes excellent operational stability by sustaining ≈90% of the initial photocurrent, even after 10 h.

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.