High Responsivity Circular Polarized Light Detectors based on Quasi Two-Dimensional Chiral Perovskite Films

Recent Progress of 2D Materials-Based Photodetectors from UV to THz Waves: Principles, Materials, and Applications

Photodetectors are one of the most critical components for future optoelectronic systems and it undergoes significant advancements to meet the growing demands of diverse applications spanning the spectrum from ultraviolet (UV) to terahertz (THz). 2D materials are very attractive for photodetector applications because of their distinct optical and electrical properties. The atomic-thin structure, high carrier mobility, low van der Waals (vdWs) interaction between layers, relatively narrower bandgap engineered through engineering, and significant absorption coefficient significantly benefit the chip-scale production and integration of 2D materials-based photodetectors. The extremely sensitive detection at ambient temperature with ultra-fast capabilities is made possible with the adaptability of 2D materials. Here, the recent progress of photodetectors based on 2D materials, covering the spectrum from UV to THz is reported. In this report, the interaction of light with 2D materials is first deliberated on in terms of optical physics. Then, various mechanisms on which detectors work, important performance parameters, important and fruitful fabrication methods, fundamental optical properties of 2D materials, various types of 2D materials-based detectors, different strategies to improve performance, and important applications of photodetectors are discussed.

Chiral 2D and quasi-2D hybrid organic inorganic perovskites: from fundamentals to applications

Chiral 2D and quasi-2D hybrid organic-inorganic perovskites (HOIPs) are emerging as promising materials for a variety of applications principally related to optoelectronics and spintronics, thanks to the combined benefits deriving from both the chiral cation and the perovskite structure. Since its recent birth, this research field is tremendously growing, focalizing on the chemical composition tuning to unveil its influence on the related functional properties as well as on developing devices for practical applications. In this review, we focused on the properties of 2D and quasi-2D chiral HOIPs, firstly providing an overview on their chiroptical behaviour followed by their potential exploitation in devices investigated so far for various applicative fields.

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.

Unraveling the influence of organic cations on tuning electronic structures and spin-splitting in two-dimensional layered organic-inorganic tin-iodine perovskites

The solar cell and light-emitting device research community is currently focusing on investigating two-dimensional (2D) hybrid perovskite materials owing to their remarkable stability and intriguing optoelectronic characteristics, which hold significant promise for various applications. In general, the introduction of chirality in hybrid perovskites arises from symmetry breaking within their inorganic frameworks. Nevertheless, despite this understanding, the specific factors driving the observed increase in splitting remain obscure due to a lack of comprehensive investigations. Our research delves into the electronic properties of 2D layered hybrid perovskites, considering their behavior with and without spin-orbit coupling. We specifically focus on effect of Rashba splitting and the impact of electronic structure variation across a range of chiral perovskites by introducing chiral organic cations with differing degrees of π-conjugation, resulting in significant changes in spin-splitting magnitude. Systematic first principles investigations confirm that the distortion of the cage and d-spacing of chiral perovskites are crucial design parameters for achieving strong spin-splitting in 2D layered perovskites. Furthermore, our investigation reveals that these systems exhibit remarkable absorption capabilities in the visible light spectrum, as demonstrated by their computed optoelectronic characteristics. The chiral perovskites described in this study, which exhibit substantial spin-splitting, present a distinctive prototype with potential implications for spintronics and photovoltaics.

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.

Pyro-Phototronic Effect Induced Circularly Polarized Light Detection with a Broadband Response

Photopyroelectric-based circularly polarized light (CPL) detection, coupling the pyro-phototronic effect and chiroptical phenomena, has provided a promising platform for high-performance CPL detectors. However, as a novel detection strategy, photopyroelectric-based CPL detection is currently restricted by the short-wave optical response, underscoring the urgent need to extend its response range. Herein, visible-to-near-infrared CPL detection induced by the pyro-phototronic effect is first realized in chiral-polar perovskites. Specifically, chiral-polar multilayered perovskites (S-BPEA)2FAPb2I7 (1-S, S-BPEA = (S)-1-4-Bromophenylethylammonium, FA = formamidinium) with spontaneous polarization shows intrinsic pyroelectric and photopyroelectric performance. Strikingly, combining its merits of the pyro-phototronic effect and intrinsic wide-spectrum spin-selective effect, chiral multilayered 1-S presents efficient photopyroelectric-based broadband CPL detection performance spanning 405-785 nm. This research first realizes photopyroelectric-based infrared CPL detection and also sheds light on developing high-performance broadband CPL detectors based on the pyro-phototronic effect in the fields of optics, optoelectronics, and spintronics.

Wafer-Scale Patterning Integration of Chiral 3D Perovskite Single Crystals toward High-Performance Full-Stokes Polarimeter

Chiral three-dimensional (3D) perovskites exhibit exceptional optoelectronic characteristics and inherent chiroptical activity, which may overcome the limitations of low-dimensional chiral optoelectronic devices and achieve superior performance. The integrated chip of high-performance arbitrary polarized light detection is one of the aims of chiral optoelectronic devices and may be achieved by chiral 3D perovskites. Herein, we first fabricate the wafer-scale integrated full-Stokes polarimeter by the synergy of unprecedented chiral 3D perovskites (R/S-PyEA)Pb2Br6 and one-step capillary-bridge assembly technology. Compared with the chiral low-dimensional perovskites, chiral 3D perovskites present smaller exciton binding energies of 57.3 meV and excellent circular dichroism (CD) absorption properties, yielding excellent circularly polarized light (CPL) photodetectors with an ultrahigh responsivity of 86.7 A W-1, an unprecedented detectivity exceeding 4.84 × 1013 Jones, a high anisotropy factor of 0.42, and high-fidelity CPL imaging with 256 pixels. Moreover, the anisotropic crystal structure also enables chiral 3D perovskites to have a large linear-polarization response with a polarized ratio of 1.52. The combination of linear-polarization and circular-polarization discrimination capabilities guarantees the achievement of a full-Stokes polarimeter. Our study provides new research insights for the large-scale patterning wafer integration of high-performance chiroptical devices.

Uniaxial-Oriented Chiral Perovskite for Flexible Full-Stokes Polarimeter

Full-Stokes polarization detection, with high integration and portability, offers an efficient path toward next-gen multi-information optoelectronic systems. Nevertheless, current techniques relying on optical filters create rigid and bulky configurations, limiting practicality. Here, a flexible, filter-less full-Stokes polarimeter featuring a uniaxial-oriented chiral perovskite film is first reported. It is found that, the strategic manipulation of the surfactant-mediated Marangoni effect during blade coating, is crucial for guiding an equilibrious mass transport to achieve oriented crystallization. Through this approach, the obtained uniaxial-oriented chiral perovskite films inherently possess anisotropy and chirality, and thereby with desired sensitivity to both linearly polarized light and circularly polarized light vectors. The uniaxial-oriented crystalline structure also improves photodetection, achieving a specific detectivity of 5.23 × 1013 Jones, surpassing non-oriented devices by 10×. The as-fabricated flexible polarimeters enable accurate capture of full-Stokes polarization without optical filters, exhibiting slight detection errors for the Stokes parameters: ΔS1 = 9.2%, ΔS2 = 8.6%, and ΔS3 = 6.5%, approaching the detection accuracy of optics-filter polarimeters. This proof of concept also demonstrates applications in matrix polarization imaging.

Fluorescence-Selective Absorption and Circularly Polarized Fluorescence Energy Transfer Assist the Generation of Multicolor Circularly Polarized Luminescence in Chiral Helical Polyacetylene-Based Janus Nanofibers

Chiroptical nanomaterials with circularly polarized luminescence (CPL) performance have aroused increasing attention. Herein, multicolor CPL-active Janus nanofibers are prepared through a simple parallel electrospinning method using chiral helical polyacetylenes as the chiral source and achiral fluorophores as the fluorescent source. Interestingly, despite a direct spatial isolation between the chiral component and the fluorescent component, blue and green CPL emissions can still be obtained due to the fluorescence-selective absorption behavior of chiral helical polyacetylenes, with a satisfactory dissymmetric factor (glum) of 2 × 10-2 and 2.5 × 10-3, respectively. Moreover, by taking advantage of the circular polarization fluorescence energy transfer process, red CPL emission is further achieved using the obtained blue and green CPL as energy donors and the achiral red fluorophore as an energy acceptor. The present work offers a facile approach to prepare multilevel-structured chiroptical materials with promising application potentials in a flexible photoelectric device.

Manipulation of Chiral Nonlinear Optical Effect by Light-Matter Strong Coupling

Light-matter strong coupling (LMSC) is an intriguing state in which light and matter are hybridized inside a cavity. It is increasingly recognized as an excellent way to control material properties without any chemical modification. Here, we show that the LMSC is a powerful state for manipulating chiral nonlinear optical (NLO) effects through the investigation of second harmonic generation (SHG) circular dichroism. At the upper polariton band in LMSC, in addition to the enhancement of SHG by more than 1 order of magnitude, the responsivity to the handedness of circularly polarized light was largely modified, where sign inversion and increase of the dissymmetry factor were achieved. Quarter waveplate rotation analysis revealed that the LMSC clearly influenced the coefficients associated with chirality in the NLO process and also contributed to the enhancement of nonlinear magnetic dipole interactions. This study demonstrated that LMSC serves as a great platform for controlling chiral and magneto-optics.

Magneto-chiral Nonlinear Optical Effect with Large Anisotropic Response in Two-Dimensional Halide Perovskite

The chiral organic-inorganic halide perovskites (OIHPs) are vital candidates for superior nonlinear optical (NLO) effects associated with circularly polarized (CP) light. NLO in chiral materials often couples with magnetic dipole (MD) transition, as well as the conventional electric dipole (ED) transition. However, the importance of MD transition in NLO process of chiral OIHPs has not yet been well recognized. Here, the circular polarized probe analysis of second harmonic generation circular dichroism (SHG-CD) provides the direct evidence that the contribution of MD leads to a large anisotropic response to CP lights in chiral OIHPs, (R-/S-MBACl)2PbI4. The thin films exhibit great sensitivity to CP lights over a wide wavelength range, and the g-value reaches up to 1.57 at the wavelength where the contribution of MD is maximized. Furthermore, it is also effective as CP light generator, outputting CP-SHG with maximum g-factor of 1.76 upon the stimulation of linearly polarized light. This study deepens the understanding of relation between chirality and magneto-optical effect, and such an efficient discrimination and generation of CP light signal is highly applicable for chirality-based sensor and optical communication devices.

Aqueous-phase dual-functional chiral perovskites for hydrogen sulfide (H2S) detection and antibacterial applications in Escherichia coli

Perovskite nanocrystals (PNCs) have attracted extensive attention for their potential applications in biology. However, only a handful of PNCs have been scrutinized in the biological domain due to issues such as instability, poor dispersion, and size inhomogeneity in polar solvents. The development of dual-functional perovskite nanomaterials with hydrogen sulfide (H2S) sensing and antibacterial capabilities is particularly intriguing. In this study, we prepared chiral quasi-two-dimensional (quasi-2D) perovskite nanomaterials, Bio(S-PEA)2CsPb2Br7 and Bio(R-PEA)2CsPb2Br7, that were uniformly dispersed in aqueous media. The effective encapsulation of methoxypolyethylene glycol amine (mPEG-NH2) improved water stability and uniformity of particle size. Circular dichroism (CD) signals were created by the successful insertion of chiral cations. These perovskites as probes showed a rapid and sensitive fluorescence quenching response to H2S, and the effect of imaging detection was observed at the Escherichia coli (E. coli) level. As antibacterial agents, their pronounced positive charge properties facilitated membrane lysis and subsequent E. coli death, indicating a significant antibacterial effect. This work has preliminary explored the application of chiral perovskites in biology and provides insight into the development of bifunctional perovskite nanomaterials for biological applications.

Research Progress on Rashba Effect in Two-Dimensional Organic-Inorganic Hybrid Lead Halide Perovskites

The Rashba effect appears in the semiconductors with an inversion-asymmetric structure and strong spin-orbit coupling, which splits the spin-degenerated band into two sub-bands with opposite spin states. The Rashba effect can not only be used to regulate carrier relaxations, thereby improving the performance of photoelectric devices, but also used to expand the applications of semiconductors in spintronics. In this mini-review, recent research progress on the Rashba effect of two-dimensional (2D) organic-inorganic hybrid perovskites is summarized. The origin and magnitude of Rashba spin splitting, layer-dependent Rashba band splitting of 2D perovskites, the Rashba effect in 2D perovskite quantum dots, a 2D/3D perovskite composite, and 2D-perovskites-based van der Waals heterostructures are discussed. Moreover, applications of the 2D Rashba effect in circularly polarized light detection are reviewed. Finally, future research to modulate the Rashba strength in 2D perovskites is prospected, which is conceived to promote the optoelectronic and spintronic applications of 2D perovskites.

Chiral Assembly of Perovskite Nanocrystals: Sensitive Discrimination of Amino Acid Enantiomers

Chirality is a widespread phenomenon in nature and in living organisms and plays an important role in living systems. The sensitive discrimination of chiral molecular enantiomers remains a challenge in the fields of chemistry and biology. Establishing a simple, fast, and efficient strategy to discriminate the spatial configuration of chiral molecular enantiomers is of great significance. Chiral perovskite nanocrystals (PNCs) have attracted much attention because of their excellent optical activity. However, it is a challenge to prepare perovskites with both chiral and fluorescence properties for chiral sensing. In this work, we synthesized two chiral fluorescent perovskite nanocrystal assembly (PNA) enantiomers by using l- or d-phenylalanine (Phe) as chiral ligands. PNA exhibited good fluorescence recognition for l- and d-proline (Pro). Homochiral interaction led to fluorescence enhancement, while heterochiral interaction led to fluorescence quenching, and there is a good linear relationship between the fluorescence changing rate and l- or d-Pro concentration. Mechanism studies show that homochiral interaction-induced fluorescence enhancement is attributed to the disassembly of chiral PNA, while no disassembly of chiral PNA was found in heterochiral interaction-induced fluorescence quenching, which is attributed to the substitution of Phe on the surface of chiral PNA by heterochiral Pro. This work suggests that chiral perovskite can be used for chiral fluorescence sensing; it will inspire the development of chiral nanomaterials and chiral optical sensors.

Ligand-Induced Chirality in ClMBA2 SnI4 2D Perovskite

Chiral perovskites possess a huge applicative potential in several areas of optoelectronics and spintronics. The development of novel lead-free perovskites with tunable properties is a key topic of current research. Herein, we report a novel lead-free chiral perovskite, namely (R/S-)ClMBA2 SnI4 (ClMBA=1-(4-chlorophenyl)ethanamine) and the corresponding racemic system. ClMBA2 SnI4 samples exhibit a low band gap (2.12 eV) together with broad emission extending in the red region of the spectrum (∼1.7 eV). Chirality transfer from the organic ligand induces chiroptical activity in the 465-530 nm range. Density functional theory calculations show a Rashba type band splitting for the chiral samples and no band splitting for the racemic isomer. Self-trapped exciton formation is at the origin of the large Stokes shift in the emission. Careful correlation with analogous lead and lead-free 2D chiral perovskites confirms the role of the symmetry-breaking distortions in the inorganic layers associated with the ligands as the source of the observed chiroptical properties providing also preliminary structure-property correlation in 2D chiral perovskites.

Temperature Dependence of Charge Transport Properties of Quasi-2D Chiral Perovskite Thin-Film Field-Effect Transistors

Chiral halide perovskite materials promise both superior light response and the capability to distinguish circularly polarized emissions, which are especially common in the fluorescence spectra of organic chiral materials. Herein, thin-film field-effect transistors (FETs) based on chiral quasi-two-dimensional perovskites are explored, and the temperature dependence of the charge carrier transport mechanism over the broad temperature range (80-300 K) is revealed. A typical p-type charge transport behavior is observed for both left-handed (S-C6H5(CN2)2NH3)2(CH3NH3)n-1PbnI3n+1 and right-handed (R-C6H5(CN2)2NH3)2(CH3NH3)n-1PbnI3n+1 chiral perovskites, with maximum carrier mobilities of 1.7 × 10-5 cm2 V-1 s-1 and 2.5 × 10-5 cm2 V-1 s-1 at around 280 K, respectively. The shallow traps with smaller activation energy (0.03 eV) hinder the carrier transport over the lower temperature regime (80-180 K), while deep traps with 1 order of magnitude larger activation energy than the shallow traps moderate the charge carrier transport in the temperature range of 180-300 K. From the charge carrier mechanism point of view, impurity scattering is established as the dominant factor from 80 K until around 280 K, while phonon scattering becomes predominant up to room temperature. Responsivities of 0.15 A W-1 and 0.14 A W-1 for left-handed and right-handed chiral perovskite FET devices are obtained.

Synthesis and Optical Properties of One Year Air-Stable Chiral Sb(III) Halide Semiconductors

Chiral hybrid metal-halide semiconductors (MHS) pose as ideal candidates for spintronic applications owing to their strong spin-orbit coupling (SOC), and long spin relaxation times. Shedding light on the underlying structure-property relationships is of paramount importance for the targeted synthesis of materials with an optimum performance. Herein, we report the synthesis and optical properties of 1D chiral (R-/S-THBTD)SbBr5 (THBTD = 4,5,6,7-tetrahydro-benzothiazole-2,6-diamine) semiconductors using a multifunctional ligand as a countercation and a structure directing agent. (R-/S-THBTD)SbBr5 feature direct and indirect band gap characteristics, exhibiting photoluminescence (PL) light emission at RT that is accompanied by a lifetime of a few ns. Circular dichroism (CD), second harmonic generation (SHG), and piezoresponse force microscopy (PFM) studies validate the chiral nature of the synthesized materials. Density functional theory (DFT) calculations revealed a Rashba/Dresselhaus (R/D) spin splitting, supported by an energy splitting (ER) of 23 and 25 meV, and a Rashba parameter (αR) of 0.23 and 0.32 eV·Å for the R and S analogs, respectively. These values are comparable to those of the 3D and 2D perovskite materials. Notably, (S-THBTD)SbBr5 has been air-stable for a year, a record performance among chiral lead-free MHS. This work demonstrates that low-dimensional, lead-free, chiral semiconductors with exceptional air stability can be acquired, without compromising spin splitting and manipulation performance.

Circular polarization-resolved ultraviolet photonic artificial synapse based on chiral perovskite

Circularly polarized light (CPL) adds a unique dimension to optical information processing and communication. Integrating CPL sensitivity with light learning and memory in a photonic artificial synapse (PAS) device holds significant value for advanced neuromorphic vision systems. However, the development of such systems has been impeded by the scarcity of suitable CPL active optoelectronic materials. In this work, we employ a helical chiral perovskite hybrid combined with single-wall carbon nanotubes to achieve circularly polarized ultraviolet neuromorphic vision sensing and imaging. The heterostructure demonstrates long-term charge storage as evidenced by multiple-pulsed transient absorption measurements and highly sensitive circular polarization-dependent photodetection, thereby enabling efficient CPL-resolved synaptic and neuromorphic behaviors. Significantly, our PAS sensor arrays adeptly visualize, discriminate, and memorize distinct circularly polarized images with up to 93% recognition accuracy in spiking neural network simulations. These findings underscore the pivotal role of chiral perovskites in advancing PAS technology and circular polarization-enhanced ultraviolet neuromorphic vision systems.

Alternating chiral and achiral spacers for constructing two-dimensional chiral hybrid perovskites toward circular-polarization-sensitive photodetection

The intrinsic integration of structural flexibility, chiroptical activity, and photoelectric properties endows the two-dimensional (2D) chiral hybrid perovskites (CHPs) with significant application potential in chiroptoelectronics and spintronics. However, the scarcity of suitable chiral organic ligands severely hinders their extensive construction, necessitating the development of new strategies for designing 2D CHPs. Herein, by exploiting a half substitution method, we created a pair of 2D CHPs with alternating cations in the interlayer space (ACI), (R/S-PPA)(PA)PbBr4 (2R/2S, PPA = 1-phenylpropylamine, PA = n-pentylamine), from the achiral Ruddlesden-Popper (RP) (PA)2PbBr4 (1). The successful chirality transfer induces 2R/2S to crystallize in the chiral P212121 space group and thus acquire appealing chiroptical activity. Consequently, the single-crystal devices of 2R exhibit good distinguishability to the left- and right-handed circularly polarized 405 nm lights with a photocurrent dissymmetric factor of 0.10 at 10 V bias. This work demonstrates an intriguing achiral RP to chiral ACI motif reconstruction in 2D halide hybrid perovskites, opening a door for expanding the family of 2D CHPs.

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.

Bright circularly polarized photoluminescence in chiral layered hybrid lead-halide perovskites

Hybrid perovskite semiconductor materials are predicted to lock chirality into place and encode asymmetry into their electronic states, while softness of their crystal lattice accommodates lattice strain to maintain high crystal quality with low defect densities, necessary for high luminescence yields. We report photoluminescence quantum efficiencies as high as 39% and degrees of circularly polarized photoluminescence of up to 52%, at room temperature, in the chiral layered hybrid lead-halide perovskites (R/S/Rac)-3BrMBA2PbI4 [3BrMBA = 1-(3-bromphenyl)-ethylamine]. Using transient chiroptical spectroscopy, we explain the excellent photoluminescence yields from suppression of nonradiative loss channels and high rates of radiative recombination. We further find that photoexcitations show polarization lifetimes that exceed the time scales of radiative decays, which rationalize the high degrees of polarized luminescence. Our findings pave the way toward high-performance solution-processed photonic systems for chiroptical applications and chiral-spintronic logic at room temperature.

Low Detection Limit Circularly Polarized Light Detection Realized by Constructing Chiral Perovskite/Si Heterostructures

Chiral perovskites have been demonstrated as promising candidates for direct circularly polarized light (CPL) detection due to their intrinsic chirality and excellent charge transport ability. However, chiral perovskite-based CPL detectors with both high distinguishability of left- and right-handed optical signals and low detection limit remain unexplored. Here, a heterostructure, (R-MPA)2 MAPb2 I7 /Si (MPA = methylphenethylamine, MA = methylammonium) is constructed, to achieve high-sensitive and low-limit CPL detection. The heterostructures with high crystalline quality and sharp interface exhibit a strong built-in electric field and a suppressed dark current, not only improving the separation and transport of the photogenerated carriers but also laying a foundation for weak CPL signals detection. Consequently, the heterostructure-based CPL detector obtains a high anisotropy factor up to 0.34 with a remarkably low CPL detection limit of 890 nW cm-2 under the self-driven mode. As a pioneering study, this work paves the way for designing high-sensitive CPL detectors that simultaneously have great distinguishing capability and low detection limit of CPL.

An Organic Chiroptical Detector Favoring Circularly Polarized Light Detection from Near-Infrared to Ultraviolet and Magnetic-Field-Amplifying Dissymmetry in Detectivity

Circularly polarized light detection has attracted growing attention because of its unique application in security surveillance and quantum optics. Here, through designing a chiral polymer as a donor, a high-performance circularly polarized light detector is fabricated, successfully enabling detection from ultraviolet (300 nm) to near-infrared (1100 nm). The chiroptical detector presents an excellent ability to distinguish right-handed and left-handed circularly polarized light, where dissymmetries in detectivity, responsivity, and electric current are obtained and then optimized. The dissymmetry in electric current can be increased from 0.18 to 0.23 once an external magnetic field is applied. This is a very rare report on the dissymmetry tunability by an external field in chiroptical detectors. Moreover, the chirality-generated orbital angular momentum is one of the key factors determining the performance of the circularly polarized light detection. Overall, the organic chiroptical detector presents excellent stability in detection, which provides great potential for future flexible and compact integrated platforms.

Unraveling chirality transfer mechanism by structural isomer-derived hydrogen bonding interaction in 2D chiral perovskite

In principle, the induced chirality of hybrid perovskites results from symmetry-breaking within inorganic frameworks. However, the detailed mechanism behind the chirality transfer remains unknown due to the lack of systematic studies. Here, using the structural isomer with different functional group location, we deduce the effect of hydrogen-bonding interaction between two building blocks on the degree of chirality transfer in inorganic frameworks. The effect of asymmetric hydrogen-bonding interaction on chirality transfer was clearly demonstrated by thorough experimental analysis. Systematic studies of crystallography parameters confirm that the different asymmetric hydrogen-bonding interactions derived from different functional group location play a key role in chirality transfer phenomena and the resulting spin-related properties of chiral perovskites. The methodology to control the asymmetry of hydrogen-bonding interaction through the small structural difference of structure isomer cation can provide rational design paradigm for unprecedented spin-related properties of chiral perovskite.

Efficient Red-Emissive Circularly Polarized Electroluminescence Enabled by Quasi-2D Perovskite with Chiral Spacer Cation

Perovskites are promising environmentally sustainable materials for circularly polarized electroluminescence (CPEL). While another chiral nonemissive layer is required for the developed perovskite-based CPEL, we report herein a highly efficient circularly polarized electroluminescence based on a single layer of quasi-2D perovskite with achiral phenethylammonium iodide (PEAI) and chiral S/R-1-(1-naphthyl)ethylammonium iodide (S/R-NEAI) as dual spacer cations. The quasi-2D perovskite was further passivated by carbazole-functionalized phosphonium. The as-fabricated film exhibits not only a circular dichroism (CD) signal but also prominent circularly polarized luminescence (CPL) activity with a maximum photoluminescence dissymmetry factor (g_lum) of ∼2.1 × 10^-3. More importantly, a highly efficient, spin-polarized light-emitting diode (LED) was fabricated based on the in situ passivated quasi-2D perovskite with a peak external quantum efficiency of 3.7% and a maximum electroluminescence dissymmetry factor (g_EL) of ∼4.0 × 10^-3.

Ferroelectricity in Hybrid Perovskites

Ferroelectric ceramics such as PbZr_xTi_1-xO₃ (PZT) are widely applied in many fields, from medical to aerospace, because of their dielectric, piezoelectric, and pyroelectric properties. In the past few years, hybrid organic-inorganic halide perovskites have gradually attracted attention for their optical and electronic properties, including ferroelectricity, and for their low fabrication costs. In this Review, we first describe techniques that are used to quantify ferroelectric figures of merit of a material. We then discuss ferroelectricity in hybrid perovskites, starting from controversies in methylammonium iodoplumbate perovskites and then focusing on low-dimensional perovskites that offer an unambiguous platform to obtain ferroelectricity. Finally, we provide examples of the application of perovskite ferroelectrics in solar cells, LEDs, and X-ray detectors. We conclude that the vast structure-property tunability makes low-dimensional hybrid perovskites promising, but they have yet to offer ferroelectric figures of merit (e.g., saturated polarization) and thermal stability (e.g., Curie temperature) competitive with those of conventional oxide perovskite ferroelectric materials.

The Interaction of 2D Materials With Circularly Polarized Light

2D materials (2DMs), due to spin-valley locking degree of freedom, exhibit strongly bound exciton and chiral optical selection rules and become promising material candidates for optoelectronic and spin/valleytronic devices. Over the last decade, the manifesting of 2D materials by circularly polarized lights expedites tremendous fascinating phenomena, such as valley/exciton Hall effect, Moiré exciton, optical Stark effect, circular dichroism, circularly polarized photoluminescence, and spintronic property. In this review, recent advance in the interaction of circularly polarized light with 2D materials covering from graphene, black phosphorous, transition metal dichalcogenides, van der Waals heterostructures as well as small proportion of quasi-2D perovskites and topological materials, is overviewed. The confronted challenges and theoretical and experimental opportunities are also discussed, attempting to accelerate the prosperity of chiral light-2DMs interactions.

Linear optical afterglow and nonlinear optical harmonic generation from chiral tin(IV) halides: the role of lattice distortions

The striking chemical variability of hybrid organic-inorganic metal halides (HOMHs) endows them with fascinating optoelectronic properties. The inorganic skeletons of HOMHs are often flexible and their lattice deformations could serve as an effective factor for enabling the functionalities of HOMHs. Here, the linear and nonlinear optical properties of zero-dimensional (0D) tin(IV) halides have been tuned by structural distortion facilitated by the chiral amines. Enantiopure α-methylbenzyl ammoniums (XMBA, X = Cl, F) effectively transfer their chirality to the inorganic scaffolds when forming the tin(IV) halides, which enables polar arrangements in their crystals and leads to outstanding second-order nonlinear optical performances. In contrast, the racemic mixture of R- and S-FMBA results in the formation of HOMHs with room temperature phosphorescence. The lower lattice deformation in (rac-FMBA)₂SnCl₆ restrains the non-radiative decay from electron-phonon coupling and facilitates the photoluminescence. Meanwhile, the marked π-π interaction stabilizes the T₁ state for phosphorescent emission. These distinct linear and nonlinear optical properties denote the important role that the lattice distortion plays in tuning the optical properties of low-dimensional HOMHs, and offer a promising perspective of 0D tin(IV) halides for applications in optoelectronic materials and devices.

Anionic ligand-induced chirality in perovskite nanoplatelets

Perovskite materials passivated by chiral ligands have recently shown unique chiroptical activity with promising optoelectronic applications. However, the ligands have been limited to chiral amines. Here, chiral phosphate molecules have been exploited to synthesize CsPbBr₃ nanoplatelets. The nanoplatelets showed a distinct circular dichroism signal and maintained their chiroptical properties after purification with anti-solvent.

Highly Anisotropic Second-Order Nonlinear Optical Effects in the Chiral Lead-Free Perovskite Spiral Microplates

Chiral metal halide perovskites with intrinsic asymmetric structures have drawn increased research interest for the application of second-order nonlinear optics (NLO). However, designing chiral perovskites with the features of a large NLO coefficient, high laser-induced damage thresholds (LDT), and environmental friendliness remains a major challenge. Herein, we have synthesized two chiral hybrid bismuth halides: (R/S-MBA)₄Bi₂Br₁₀ spiral structure microplates, templated by chiral (R/S)-methylbenzylamine (R/S-MBA). The as-grown chiral lead-free perovskite spiral microplates exhibit a recorded second harmonic generation (SHG) effect with a large effective second-order NLO coefficient (d_eff) of 11.9 pm V^-1 and a high LDT of up to 59.2 mJ cm^-2. More importantly, the twisted screw structures show competitive circular polarization sensitivity at 1200 nm with an anisotropy factor (g_SHG-CD) of 0.58, which is about 3 times higher than that of reported Pb-based chiral perovskites. These findings provide a new platform to design multifunctional lead-free chiral perovskites for nonlinear photonic applications.

Metal-Photoswitch Friendship: From Photochromic Complexes to Functional Materials

Cooperative metal-photoswitch interfaces comprise an application-driven field which is based on strategic coupling of metal cations and organic photochromic molecules to advance the behavior of both components, resulting in dynamic molecular and material properties controlled through external stimuli. In this Perspective, we highlight the ways in which metal-photoswitch interplay can be utilized as a tool to modulate a system's physicochemical properties and performance in a variety of structural motifs, including discrete molecular complexes or cages, as well as periodic structures such as metal-organic frameworks. This Perspective starts with photochromic molecular complexes as the smallest subunit in which metal-photoswitch interactions can occur, and progresses toward functional materials. In particular, we explore the role of the metal-photoswitch relationship for gaining fundamental knowledge of switchable electronic and magnetic properties, as well as in the design of stimuli-responsive sensors, optically gated memory devices, catalysts, and photodynamic therapeutic agents. The abundance of stimuli-responsive systems in the natural world only foreshadows the creative directions that will uncover the full potential of metal-photoswitch interactions in the coming years.

Spin-Selective Charge Transport in Lead-Free Chiral Perovskites: The Key towards High-Anisotropy in Circularly-Polarized Light Detection

A pair of zero-dimensional lead-free chiral perovskites is introduced towards the detection of circularly polarized light (CPL). Although spin-polarized carriers are generated in the perovskites under the CPL, the absorption anisotropy remained low leading to mostly similar density of photogenerated carriers under the two CPLs. Interestingly, due to the intrinsic chirality in the perovskites, they exhibited chirality-induced spin-selectivity (CISS) allowing the transport of only one type of spin-half states. A high anisotropy in photocurrent along the out-of-plane direction has therefore appeared resulting in a spin-dependent photovoltaic effect in vertical heterojunction devices and making them suitable for CPL detection. While a self-powered CPL detector showed a limited (but one of the highest to date) anisotropy factor of 0.3 due to possible spin-flips during the transport process, the factor rose to 0.6 under bias prompting extension of the effective spin-diffusion length.

Multispectral and Circular Polarization-Sensitive Carbon Dot-Polydiacetylene Capacitive Photodetector

Multispectral photodetectors (MSPs) and circularly polarized light (CPL) sensors are important in opto-electronics, photonics, and imaging. A capacitive photodetector consisting of an interdigitated electrode coated with carbon dot/anthraquinone-polydiacetylene is constructed. Photoexcitation of the carbon dots induces transient electron transfer to the anthraquinone moieties, and concomitant change in the film dielectric constant and recorded capacitance. This unique photodetection mechanism furnishes wavelength selectivity that is solely determined by the absorbance of the carbon dots incorporated in the anthraquinone-polydiacetylene matrix. Accordingly, employing an array of polymerized-anthraquinone photodetector films comprising carbon dots (C-dots) exhibiting different excitation wavelengths yielded optical "capacitive fingerprints" in a broad spectral range (350-650 nm). Furthermore, circular light polarization selectivity is achieved through chiral polymerization of the polydiacetylene framework. The carbon dot/anthraquinone-polydiacetylene capacitive photodetector features rapid photo-response, high fidelity, and recyclability as the redox reactions of anthraquinone are fully reversible. The carbon dot/anthraquinone-polydiacetylene platform is inexpensive, easy to fabricate, and consists of environmentally friendly materials.

Multilayered Alternating-Cations-Intercalation Chiral Hybrid Perovskites with High Circular Polarization Sensitivity

Multilayered chiral hybrid perovskites are highly desired for highly-sensitive circularly polarized light (CPL) detection rooted in their efficient charge transport and strong chiroptical activity. However, designing multilayered chiral hybrid perovskites remains a huge challenge. Here, through pairing achiral ethylamine (EA)-chiral arylamine in the interlayer space, multilayered chiral alternating cations intercalation-type (ACI) hybrid perovskites (R-/S-PPA) EA₂ Pb₂ Br₇ (PPA = 1-phenylpropylamine) are successfully obtained. Significantly, perovskitizer EA extends the thickness of the quantum well and alternating space cation EA greatly alleviates in-plane tilting distortions of adjacent metal halide octahedra, providing fast channels for in-plane carrier transport. Consequently, single-crystal photodetectors of (R-/S-PPA) EA₂ Pb₂ Br₇ exhibit high circular polarization sensitivity with a large anisotropy factor of 0.3, which falls around the highest value among the layered hybrid perovskites. In addition, a fast responding rate (τ_r )of 308 µs and a high CPL-detectivity of 8 × 10¹² Jones are also presented. This work opens up a new perspective to design multilayered chiral hybrid perovskites for high-sensitive CPL detection.

Chiral Rashba Ferroelectrics for Circularly Polarized Light Detection

Direct detection of circularly polarized light (CPL) is a challenging task due to limited materials and ambiguous structure-property relationships that lead to low distinguishability of the light helicities. Perovskite ferroelectric semiconductors incorporating chirality provide new opportunities in dealing with this issue. Herein, a pair of 2D chiral perovskite ferroelectrics is reported, which have enhanced CPL detection performance due to interplays among lattice, photon, charge, spin, and orbit. The chirality-transfer-induced chiral&polar ferroelectric phase enhances the asymmetric nature of the photoactive sublattice and achieves a switchable self-powered detection via the bulk photovoltaic effect. The single-crystal-based device exhibits a CPL-sensitive detection performance under 430 nm with an asymmetric factor of 0.20 for left- and right-CPL differentiation, about two times that of the pure chiral counterparts. The enhanced CPL detection performance is ascribed to the Rashba-Dresselhaus effect that originates from the bulk inversion asymmetry and strong spin-orbit coupling, shown with a large Rashba coefficient, which is demonstrated by density functional theory calculation and circularly polarized light excited photoluminescence measurement. These results provide new perspectives on chiral Rashba ferroelectric semiconductors for direct CPL detection and ferroelectrics-based chiroptics and spintronics.

Strong two-photon absorption induced by energy funneling in chiral quasi-2D perovskites

Quasi-2D Ruddlesden-Popper-type perovskites (RPPs) exhibit excellent nonlinear optical properties due to their multiple quantum well structures with large exciton binding energy. Herein, we introduce chiral organic molecules into RPPs and investigate their optical properties. It is found that the chiral RPPs possess effective circular dichroism in the ultraviolet to visible wavelengths. Two-photon absorption (TPA)-induced efficient energy funneling from small- to large-n domains is observed in the chiral RPP films, which induces strong TPA with a coefficient up to 4.98 cm MW^-1. This work will broaden the application of quasi-2D RPPs in chirality-related nonlinear photonic devices.

Chain-to-Layer Dimensionality Engineering of Chiral Hybrid Perovskites to Realize Passive Highly Circular-Polarization-Sensitive Photodetection

Chiral hybrid perovskites (CHPs), aggregating chirality and favorable semiconducting properties in one, have taken a prominent position in direct circularly polarized light detection (CPL). However, passive high circular polarization sensitivity (g_res) photodetection in CHPs is still elusive and challenging. Benefitting from efficient control and turning of carrier transport of CHPs by dimensional engineering, here, we unprecedentedly proposed a chain-to-layer dimensionality engineering to realize high-g_res passive photodetection. Two novel 2D layered CHPs (R/S-PPA)EAPbBr₄ (2R/2S) (PPA = 1-phenylpropylamine, EA = ethylammonium) are successfully synthesized by alloying an EA cation with small steric hindrance into the chained CHPs (R/S-PPA)PbBr₃ (1R/1S). Particularly, compared with the neglectable photoresponse in 1R, the obtained 2R by chain-to-layer dimensionality engineering gives rise to an excellent photoconductivity and robust polar photovoltage effect (PPE) with a giant open-circuit voltage of 2.5 V. Furthermore, such PPE promotes realizing an impressive g_res in 2R up to 0.42 at zero bias because of the independent separation of photoexcited carriers, which is the highest value among the reported layered chiral perovskites. This work paves the way for the vigorous development of higher dimensional CHPs and will reveal their applications in the field of passive high-g_res CPL detection.

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

Chiral perovskites have emerged as promising candidates for polarization-sensing materials. Despite their excellent chiroptical properties, the nature of their multiple-quantum-well structures is a critical hurdle for polarization-based and spintronic applications. Furthermore, as the origin of chiroptical activity in chiral perovskites is still illusive, the strategy for simultaneously enhancing the chiroptical activity and charge transport has not yet been reported. Here, we demonstrated that incorporating a Lewis base into the lattice can effectively tune the chiroptical response and electrical properties of chiral perovskites. Through solid-state nuclear magnetic resonance spectroscopic measurements and theoretical calculations, it was demonstrated that the material property manipulation resulted from the change in the time-averaged structure induced by the Lewis base. Finally, as a preliminary proof of concept, a vertical-type circularly polarized light photodetector based on chiral perovskites was developed, exhibiting an outstanding performance with a distinguishability of 0.27 and a responsivity of 0.43 A W^-1.

Best practices in the measurement of circularly polarised photodetectors

Circularly polarised light will revolutionise emerging technologies, including encrypted light-based communications, quantum computing, bioimaging and multi-channel data processing. In order to make use of these remarkable opportunities, high performance photodetectors that can accurately differentiate between left- and right-handed circularly polarised light are desperately needed. Whilst this potential has resulted in considerable research interest in chiral materials and circularly polarised photodetecting devices, their translation into real-world technologies is limited by non-standardised reporting and testing protocols. This mini-review provides an accessible introduction into the working principles of circularly polarised photodetectors and a comprehensive overview of the performance metrics of state-of-the-art devices. We propose a rigorous device characterisation procedure that will allow for standardised evaluation of novel devices, which we hope will accelerate research and investment in this area.

Chiral Hybrid Copper(I) Iodide Single Crystals Enable Highly Selective Ultraviolet-Pumped Circularly Polarized Luminescence Applications

Light-emitting diodes (LEDs) with the circularly polarized luminescence features have attracted attention to the promising applications ranging from solid-state lighting and displays to bioencoding and anticounterfeiting. The prerequisite of circularly polarized luminescence is highly emissive chiral materials. Here, we demonstrated that (R/S-MBA)₄Cu₄I₈·2H₂O (MBA = α-methylbenzylaminium) and acentric Gua₆Cu₄I₁₀ (Gua = guanidinium) single crystals were grown on the basis of Gua₃Cu₂I₅ by the slow evaporation method. (R/S-MBA)₄Cu₄I₈·2H₂O single crystals exhibited excellent circularly polarized luminescence (CPL) characteristics. More importantly, ultraviolet-pumped LEDs (UV-LEDs) based on (R/S-MBA)₄Cu₄I₈·2H₂O and Gua₆Cu₄I₁₀ single crystals exhibit a higher optical selectivity when exposed to right-handed and left-handed circular polarization (RCP and LCP) conditions. (S-MBA)₄Cu₄I₈·2H₂O single crystals and Gua₆Cu₄I₁₀ single crystals induced by the (R)-MBA cation exhibit the different polarized light intensities at PL peak positions in different λ/4 waveplate polarizer angle directions, which provides new possibilities for the further applications from 3D displays to spintronics, as well as anticounterfeiting.