Dimensional and Doping Engineering of Chiral Perovskites with Enhanced Spin Selectivity for Green Emissive Spin Light-Emitting Diodes.

Chiral perovskites play a pivotal role in spintronics and optoelectronic systems attributed to their chiral-induced spin selectivity (CISS) effect. Specifically, they allow for spin-polarized charge transport in spin light-emitting diodes (LEDs), yielding circularly polarized electroluminescence at room temperature without external magnetic fields. However, chiral lead bromide-based perovskites have yet to achieve high-performance green emissive spin-LEDs, owing to limited CISS effects and charge transport. Herein, we employ dimensional regulation and Sn2+-doping to optimize chiral bromide-based perovskite architecture for green emissive spin-LEDs. The optimized (PEA)x(S/R-PRDA)2-xSn0.1Pb0.9Br4 chiral perovskite film exhibits an enhanced CISS effect, higher hole mobility, and better energy level alignment with the emissive layer. These improvements allow us to fabricate green emissive spin-LEDs with an external quantum efficiency (EQE) of 5.7% and an asymmetry factor |gCP-EL| of 1.1 × 10-3. This work highlights the importance of tailored perovskite architectures and doping strategies in advancing spintronics for optoelectronic applications.

Lead-Free Chiral Perovskite for High Degree of Circularly Polarized Light Emission and Spin Injection.

We report a zero-dimensional (0D) lead-free chiral perovskite (S-/R-MBA)4Bi2I10 with a high degree of circularly polarized light (CPL) emission. Our 0D lead-free chiral perovskite exhibits an average degree of circular polarization (DOCP) of 19.8% at 78 K under linearly polarized laser excitation, and the maximum DOCP can reach 25.8%, which is 40 times higher than the highest DOCP of 0.5% in all reported lead-free chiral perovskites to the best of our knowledge. The high DOCP of (S-/R-MBA)4Bi2I10 is attributed to the free exciton emission with a Huang-Rhys factor of 2.8. In contrast, all the lead-free chiral perovskites in prior reports are dominant by self-trapped exciton in which the spin relaxation reduces DOCP dramatically. Moreover, we realize the manipulation of the valley degree of freedom of monolayer WSe2 by using the spin injection of the 0D chiral lead-free perovskites. Our results provide a new perspective to develop lead-free chiral perovskite devices for CPL light source, spintronics, and valleytronics.

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.

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.

Full-Stokes Polarimeter Based on Chiral Perovskites with Chirality and Large Optical Anisotropy.

Full-Stokes polarimeters, equipped with the capability of discriminating light polarization states, can find important applications in various optical and optoelectronic devices. Nevertheless, currently most full-Stokes polarimeters require complex and bulky optical elements or optical metasystems integrated with metasurfaces, which can increase the cost and cause energy loss. Here, the anisotropy of chiral 2D perovskite single crystals is explored and the full-Stokes polarimeter based on pure chiral 2D perovskite single crystals is reported. By using optical anisotropy and the ability to distinguish the helicity of the circularly polarized light, chiral 2D perovskite polarimeter integrates the polarizer, waveplate, and photodetector together and thus can be able to discriminate the polarization states of light. The as-fabricated device exhibits a photoresponsivity of 0.136 A W-1 and a detectivity of 1.2 × 1010 Jones. This study provides a paradigm to construct filterless on-chip Stokes polarimeter with great simplicity and low cost.

A Chiral Reduced-Dimension Perovskite for an Efficient Flexible Circularly Polarized Light Photodetector.

Chiral quasi-2D perovskite single crystals (SCs) were investigated for their circular polarized light (CPL) detecting capability. Quasi-2D chiral perovskites, [(R)-ß-MPA]2 MAPb2 I7 ((R)-ß-MPA=(R)-(+)-ß-methylphenethylamine, MA=methylammonium), have intrinsic chirality and the capability to distinguish different polarization states of CPL photons. Corresponding quasi-2D SCs CPL photodetector exhibit excellent detection performance. In particular, our device responsivity is almost one order of magnitude higher than the reported 2D perovskite CPL detectors to date. The crystallization dynamics of the film were modulated to facilitate its carrier transport. Parallel oriented perovskite films with a homogeneous energy landscape is crucial to maximize the carrier collection efficiency. The photodetector also exhibits superior mechanical flexibility and durability, representing a promising candidate for sensitive and robust CPL photodetectors.

Chiral Perovskites: Promising Materials toward Next-Generation Optoelectronics.

Halide perovskites have emerged as a type of extremely promising material for their diverse chemical and electronic structures along with their brilliant optoelectronic properties. The introduction of chirality into perovskite scaffolds, generating a novel concept of chiral perovskite materials, offers an immense step forward toward the development of smart optoelectronic and spintronic materials and devices. The present Review summarizes recent advances in such an emerging field regarding the design and construction of chiral perovskite materials, along with their optoelectronic performances. In addition, an outlook of future challenges as well as the potential significance of the chiral perovskite family on the optical communication is proposed.

Spin Quantum Dot Light-Emitting Diodes Enabled by 2D Chiral Perovskite with Spin-Dependent Carrier Transport.

Chiral-induced spin selectivity (CISS) effect provides innovative approach to spintronics and quantum-based devices for chiral materials. Different from the conventional ferromagnetic devices, the application of CISS effect is potential to operate under room temperature and zero applied magnetic field. Low dimensional chiral perovskites by introducing chiral amines are beginning to show significant CISS effect for spin injection, but research on chiral perovskites is still in its infancy, especially on spin-light emitting diode (spin-LED) construction. Here, the spin-QLEDs enabled by 2D chiral perovskites as CISS layer for spin-dependent carrier injection and CdSe/ZnS quantum dots (QDs) as light emitting layer are reported. The regulation pattern of the chirality and thickness of chiral perovskites, which affects the circularly polarized electroluminescence (CP-EL) emission of spin-QLED, is discovered. Notably, the spin injection polarization of 2D chiral perovskites is higher than 80% and the CP-EL asymmetric factor (gCP-EL ) achieves up to 1.6 × 10-2 . Consequently, this work opens up a new and effective approach for high-performance spin-LEDs.

Unusual Pressure-Induced Self-Trapped Exciton to Free Exciton Transfer in Chiral 2D Lead Bromide Perovskites.

The phenomenon of pressure-induced emission alterations related to complex excitonic dynamics in 2D lead halide perovskites (LHPs) has gained considerable attention for understanding their structure-property relationship and obtaining inaccessible luminescence under ambient conditions. However, the well-known pressure-induced emissions are limited to the formation of self-trapped excitons (STEs) due to the structural distortion under compression, which goes against the advantage of the highly pure emission of LHPs. Here, the pressure-induced detrapping from STEs to free excitons (FEs) accompanied by the dramatic transition from broadband orangish emission to narrow blue emission has been achieved in chiral 2D LHPs and R- and S-[4MeOPEA]2PbBr4, (4MeOPEA = 4-methoxy-α-methylbenzylammonium). The combined experimental and calculated results reveal that the distortion level of PbBr6 octahedra of R- and S-[4MeOPEA]2PbBr4 exhibits an unusually significant reduction as the applied pressure increases, which leads to decreased electron-phonon coupling and self-trapped energy barrier and consequently enables the detrapping of STEs to FEs. This work illustrates the dramatic exciton transfer in 2D LHPs and highlights the potential for realizing highly efficient and pure light emissions by manipulating the structural distortion via strain engineering.

Introducing Chiro-optical Activities in Photonic Synapses for Neuromorphic Computing and In-Memory Logic Operations.

In artificial synaptic devices aimed at mimicking neuromorphic computing systems, electrical or optical pulses, or both, are generally used as stimuli. In this work, we introduce chiral materials for tailoring the characteristics of photonic synaptic devices to achieve handedness-dependent neuromorphic computing and in-memory logic gates. In devices based on a pair of chiral perovskites, the use of circularly polarized light (CPL) as the optical stimuli mimicked a series of electrical and opto-synaptic functionalities in order to emulate the multifunctional complex behavior of the human brain. Upon illumination in this two-terminal device, anisotropy in current has been observed due to the out-of-plane carrier transport, originating from spin-selective carrier transport. More importantly, the logic gate achieved in devices based on optoelectronic memristors turned out to be chirality-dependent; while an R-device functioned as an AND gate, the device based on the same perovskite of the opposite chirality (S-device) acted as a NOR gate toward in-memory logic operations. These findings in chiral perovskite-based artificial synapses can identify further strategies for future neuromorphic computing, vision simulation, and artificial intelligence.

Chirality Versus Symmetry: Electron's Spin Selectivity in Nonpolar Chiral Lead-Bromide Perovskites.

In the last decade, chirality-induced spin selectivity (CISS), the spin-selective electron transport through chiral molecules, has been described in a large range of materials, from insulators to superconductors. Because more experimental studies are desired for the theoretical understanding of the CISS effect, chiral metal-halide semiconductors may contribute to the field thanks to their chiroptical and spintronic properties. In this regard, this work uses new chiral organic cations S-HP1A and R-HP1A (HP1A = 2-hydroxy-propyl-1-ammonium) to prepare 2D chiral halide perovskites (HPs) which crystallize in the enantiomorphic space groups P43 21 2 and P41 21 2, respectively. The fourfold symmetry induces antiferroelectricity along the stacking axis which, combined to incomplete Rashba-like splitting in each individual 2D polar layer, results in rare spin textures in the band structure. As revealed by magnetic conductive-probe atomic force microscopy (AFM) measurements, these materials show CISS effect with partial spin polarization (SP; ±40-45%). This incomplete effect is efficient enough to drive a chiro-spintronic device as demonstrated by the fabrication of spin valve devices with magnetoresistance (MR) responses up to 250 K. Therefore, these stable lead-bromide HP materials not only represent interesting candidates for spintronic applications but also reveal the importance of polar symmetry-breaking topology for spin selectivity.

Chiroptical Response Inversion and Enhancement of Room-Temperature Exciton-Polaritons Using 2D Chirality in Perovskites.

Although chiral semiconductors have shown promising progress in direct circularly polarized light (CPL) detection and emission, they still face potential challenges. A chirality-switching mechanism or approach integrating two enantiomers is needed to discriminate the handedness of a given CPL; additionally, a large material volume is required for sufficient chiroptical interaction. These two requirements pose significant obstacles to the simplification and miniaturization of the devices. Here, room-temperature chiral polaritons fulfilling dual-handedness functions and exhibiting a more-than-two-order enhancement of the chiroptical signal are demonstrated, by embedding a 40 nm-thick perovskite film with a 2D chiroptical effect into a Fabry-Pérot cavity. By mixing chiral perovskites with different crystal structures, a pronounced 2D chiroptical effect is accomplished in the perovskite film, featured by an inverted chiroptical response for counter-propagating CPL. This inversion behavior matches the photonic handedness switch during CPL circulation in the Fabry-Pérot cavity, thus harvesting giant enhancement of the chiroptical response. Furthermore, affected by the unique quarter-wave-plate effects, the polariton emission achieves a chiral dissymmetry of ±4% (for the emission from the front and the back sides). The room-temperature polaritons with the strong dissymmetric chiroptical interaction shall have implications on a fundamental level and future on-chip applications for biomolecule analysis and quantum computing.

Direct Detection of Near-Infrared Circularly Polarized Light via Precisely Designed Chiral Perovskite Heterostructures.

Chiral metal halide perovskites (CMHPs) have recently shown great potential for direct circularly polarized light (CPL) detection. However, owing to the limited cutoff wavelength edge of these CMHPs, most of the detectors presented thus far are characterized only in the ultraviolet and visible range; CMHPs that target at the near-infrared (NIR) region are still greatly desired. Here, we design a novel CMHP heterostructure, synthesized via solution-processed epitaxial growth of crystalline 3D MAPbI3 on a 2D chiral (R-BPEA)2PbI4 (R-BPEA = (R)-1-(4-bromophenyl)ethylammonium) crystal, and provide the first demonstration of self-powered direct NIR-CPL detection. Compared with individual chiral (R-BPEA)2PbI4, the heterostructure not only retains the spin selectivity but also allows much broader absorbance, especially beyond 780 nm, where the (R-BPEA)2PbI4 cannot absorb. Furthermore, the built-in electric potential in the heterojunction forces spontaneous separation/transport of photogenerated carriers, enabling the fabrication of devices operating without external energy supply. By making use of the abovementioned advantages, the self-powered CPL detectors of the (R-BPEA)2PbI4/MAPbI3 heterostructures hence show competitive circular polarization sensitivity at 785 nm with a high anisotropy factor of up to 0.25. In addition, a large on/off switching ratio of ∼105 and an impressive detectivity of ∼1010 Jones are also achieved. As a pioneer study, our results may broaden the material scope for future chiroptical devices based on CMHPs.

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.

Chiral Helical Polymer/Perovskite Hybrid Nanofibers with Intense Circularly Polarized Luminescence.

Chiral perovskites with circularly polarized luminescence (CPL) performance have attracted tremendous attention. This contribution reports a convenient and universal strategy for constructing chiral helical polymer/perovskite hybrid nanofibers with outstanding CPL properties. The hybrid nanofibers are prepared through a one-step electrospinning method in which chiral helical polyacetylenes, perovskite nanocrystals, and polyacrylonitrile serve as a handed-selective fluorescence filter, fluorescent source, and electrospinning matrix, respectively. Specially, perovskite nanocrystals are in situ formed during the electrospinning process, which avoids the tedious process for preparing and purifying perovskites. The prepared hybrid nanofibers all exhibit good long-time stability in air, owing to the effective protection effect of polymer matrix. More importantly, intense CPL emissions with high dissymmetry factor up to 10-2 level are obtained in the hybrid nanofibers. Furthermore, the emission color of CPL can be easily tuned by adjusting the precursors of perovskites. This work provides an efficient technique toward various kinds of CPL-active perovskite nanomaterials for both scientific research and future practical applications.

Chiral Perovskites for Next-Generation Photonics: From Chirality Transfer to Chiroptical Activity.

Organic-inorganic hybrid halide perovskites (OIHPs) are commonly used as prototypical materials for various applications, including photovoltaics, photodetectors, and light-emitting devices. Since the chiroptical properties of OIHPs are deciphered in 2017, chiral OIHPs have been rediscovered as new hybrid systems comprising chiral organic molecules and achiral inorganic octahedral layers. Owing to their exceptional optoelectrical properties and structural flexibility, chiral OIHPs have received a considerable amount of attention in chiral photonics, chiroptoelectronics, spintronics, and ferroelectrics. Despite their intriguing chiral properties, the transfer mechanism from chiral molecules to achiral semiconductors has not been extensively investigated. Furthermore, an in-depth understanding of the origin of chiroptical activity is still elusive. In this review article, recent advances in the chiroptical activities of chiral OIHPs and polarization-based devices adopting chiral OIHPs are comprehensively discussed, and insight into the underlying chirality transfer mechanism based on theoretical considerations is provided. This comprehensive survey, with an emphasis on the chirality transfer mechanism, will help readers understand the chiroptical properties of OIHPs, which are crucial for the development of spin-based photonic and optoelectronic devices. Additionally, promising strategies to exploit the potential of chiral OIHPs are also discussed.

Theoretical Prediction of Chiral 3D Hybrid Organic-Inorganic Perovskites.

Hybrid organic-inorganic perovskites (HOIPs), in particular 3D HOIPs, have demonstrated remarkable properties, including ultralong charge-carrier diffusion lengths, high dielectric constants, low trap densities, tunable absorption and emission wavelengths, strong spin-orbit coupling, and large Rashba splitting. These superior properties have generated intensive research interest in HOIPs for high-performance optoelectronics and spintronics. Here, 3D hybrid organic-inorganic perovskites that implant chirality through introducing the chiral methylammonium cation are demonstrated. Based on structural optimization, phonon spectra, formation energy, and ab initio molecular dynamics simulations, it is found that the chirality of the chiral cations can be successfully transferred to the framework of 3D HOIPs, and the resulting 3D chiral HOIPs are both kinetically and thermodynamically stable. Combining chirality with the impressive optical, electrical, and spintronic properties of 3D perovskites, 3D chiral perovskites is of great interest in the fields of piezoelectricity, pyroelectricity, ferroelectricity, topological quantum engineering, circularly polarized optoelectronics, and spintronics.