Perovskite-based photodetectors: materials and devices

Origin of Dopant-Carrier Exchange Coupling and Excitonic Zeeman Splitting in Mn2+-Doped Lead Halide Perovskite Nanocrystals

Low-dimensional metal halide perovskites have unique optical and electrical properties that render them attractive for the design of diluted magnetic semiconductors. However, the nature of dopant-exciton exchange interactions that result in spin-polarization of host-lattice charge carriers as a basis for spintronics remains unexplored. Here, we investigate Mn2+-doped CsPbCl3 nanocrystals using magnetic circular dichroism spectroscopy and show that Mn2+ dopants induce excitonic Zeeman splitting which is strongly dependent on the nature of the band-edge structure. We demonstrate that the largest splitting corresponds to exchange interactions involving the excited state at the M-point along the spin-orbit split-off conduction band edge. This splitting gives rise to an absorption-like C-term excitonic MCD signal, with the estimated effective g-factor (geff) of ca. 70. The results of this work help resolve the assignment of absorption transitions observed for metal halide perovskite nanocrystals and allow for a design of new diluted magnetic semiconductor materials for spintronics applications.

Perovskite versus Standard Photodetectors

Perovskites have been largely implemented into optoelectronics as they provide several advantages such as long carrier diffusion length, high absorption coefficient, high carrier mobility, shallow defect levels and finally, high crystal quality. The brisk technological development of perovskite devices is connected to their relative simplicity, high-efficiency processing and low production cost. Significant improvement has been made in the detection performance and the photodetectors' design, especially operating in the visible (VIS) and near-infrared (NIR) regions. This paper attempts to determine the importance of those devices in the broad group of standard VIS and NIR detectors. The paper evaluates the most important parameters of perovskite detectors, including current responsivity (R), detectivity (D*) and response time (τ), compared to the standard photodiodes (PDs) available on the commercial market. The conclusions presented in this work are based on an analysis of the reported data in the vast pieces of literature. A large discrepancy is observed in the demonstrated R and D*, which may be due to two reasons: immature device technology and erroneous D* estimates. The published performance at room temperature is even higher than that reported for typical detectors. The utmost D* for perovskite detectors is three to four orders of magnitude higher than commercially available VIS PDs. Some papers report a D* close to the physical limit defined by signal fluctuations and background radiation. However, it is likely that this performance is overestimated. Finally, the paper concludes with an attempt to determine the progress of perovskite optoelectronic devices in the future.

Printed On-Chip Perovskite Heterostructure Arrays for Optical Switchable Logic Gates

The use of optoelectronic devices for high-speed and low-power data transmission and computing is considered in the next-generation logic circuits. Heterostructures, which can generate and transmit photoresponse signals dealing with different input lights, are highly desirable for optoelectronic logic gates. Here, the printed on-chip perovskite heterostructures are demonstrated to achieve optical-controlled "AND" and "OR" optoelectronic logic gates. Perovskite heterostructures are printed with a high degree of control over composition, site, and crystallization. Different regions of the printed perovskite heterostructures exhibit distinguishable photoresponse to varied wavelengths of input lights, which can be utilized to achieve optical-controlled logic functions. Correspondingly, parallel operations of the two logic gates ("AND" and "OR") by way of choosing the output electrodes under the single perovskite heterostructure. Benefiting from the uniform crystallization and strict alignment of the printed perovskite heterostructures, the integrated 3 × 3 pixels all exhibit 100% logic operation accuracy. Finally, optical-controlled logic gates responding to multiwavelength light can be printed on the predesigned microelectrodes as the on-chip integrated circuits. This printing strategy allows for integrating heterostructure-based optical and electronic devices from a unit-scale device to a system-scale device.

In Situ Growth Method for Large-Area Flexible Perovskite Nanocrystal Films

Metal halide perovskites have shown unique advantages compared with traditional optoelectronic materials. Currently, perovskite films are commonly produced by either multi-step spin coating or vapor deposition techniques. However, both methods face challenges regarding large-scale production. Herein, we propose a straightforward in situ growth method for the fabrication of CsPbBr3 nanocrystal films. The films cover an area over 5.5 cm × 5.5 cm, with precise thickness control of a few microns and decent uniformity. Moreover, we demonstrate that the incorporation of magnesium ions into the perovskite enhances crystallization and effectively passivates surface defects, thereby further enhancing luminous efficiency. By integrating this approach with a silicon photodiode detector, we observe an increase in responsivity from 1.68 × 10-2 A/W to 3.72 × 10-2 A/W at a 365 nm ultraviolet wavelength.

Dense Perovskite Thick Film Enabled by Saturated Solution Filling for Sensitive X-ray Detection and Imaging

Thick polycrystalline perovskite films synthesized by using solution processes show great potential in X-ray detection applications. However, due to the evaporation of the solvent, many pinholes and defects appear in the thick films, which deteriorate their optoelectronic properties and diminish their X-ray detection performance. Therefore, the preparation of large area and dense perovskite thick films is desired. Herein, we propose an effective strategy of filling the pores with a saturated precursor solution. By adding the saturated perovskite solution to the polycrystalline perovskite thick film, the original perovskite film will not be destroyed because of the solution-solute equilibrium relationship. Instead, it promotes in situ crystal growth within the thick film during the annealing process. The loosely packed grains in the original thick perovskite film are connected, and the pores and defects are partially filled and fixed. Finally, a much denser perovskite thick film with improved optoelectronic properties has been obtained. The optimized thick film exhibits an X-ray sensitivity of 1616.01 μC Gyair-1 cm-2 under an electric field of 44.44 V mm-1 and a low detection limit of 28.64 nGyair s-1 under an electric field of 22.22 V mm-1. These values exceed the 323.86 μC Gyair-1 cm-2 and 40.52 nGyair s-1 of the pristine perovskite thick film measured under the same conditions. The optimized thick film also shows promising working stability and X-ray imaging capability.

Controlling Ionic Conductivity in Organometallic Ionic Liquids through Light-Induced Coordination Polymer Formation and Thermal Reversion

Owing to their high ionic conductivity and negligible vapor pressure, ionic liquids (ILs) find applications in various electronic devices. However, fabricating IL-based photocontrollable devices remains a challenge. In this study, we developed organometallic ILs with reversible light- and heat-controlled ionic conductivities for potential use in tunable devices. The physical properties and stimulus responses of ILs containing a cationic sandwich Ru complex with two coordinating substituents were investigated. UV photoirradiation of these ILs triggered cation photodissociation, resulting in their transformation into viscoelastic coordination polymers wherein the coordinating substituents bridged the Ru centers. Owing to the anion coordination, salts with coordinating anions such as CF3SO2NCN-, B(CN)4-, and BF2(CN)2- exhibited faster response and higher conversion than those with noncoordinating anions including (FSO2)2N- and (CF3SO2)2N-. All photoproducts reverted to their original ILs upon heating, except for the photoproduct of the BF2(CN)2 salt, which decomposed upon heating. Light- and heat-induced reversible changes occur in most cases between the high-ionic-conductive IL state and low-ionic-conductive coordination polymer state. Unlike previously reported ILs with three or one cation substituent, the current ILs exhibited both high reactivity and large ionic conductivity changes.

Graphene photodetectors integrated with silicon and perovskite quantum dots

Photodetectors (PDs) play a crucial role in imaging, sensing, communication systems, etc. Graphene (Gr), a leading two-dimensional material, has demonstrated significant potential for photodetection in recent years. However, its relatively weak interaction with light poses challenges for practical applications. The integration of silicon (Si) and perovskite quantum dots (PQDs) has opened new avenues for Gr in the realm of next-generation optoelectronics. This review provides a comprehensive investigation of Gr/Si Schottky junction PDs and Gr/PQD hybrid PDs as well as their heterostructures. The operating principles, design, fabrication, optimization strategies, and typical applications of these devices are studied and summarized. Through these discussions, we aim to illuminate the current challenges and offer insights into future directions in this rapidly evolving field.

Boosted Second Harmonic Generation of a Chiral Hybrid Lead Halide Resonant to Charge Transfer Exciton from Metal Halide Octahedra to Ligand

Chiral hybrid organic-inorganic metal halides (HOMHs) offer an ideal platform for the advancement of second-order nonlinear optical (NLO) materials owing to their inherent noncentrosymmetric structures. The enhancement of optical nonlinearity of chiral HOMHs could be achieved by matching the free exciton and/or self-trapped exciton energy levels with desired NLO frequencies. However, the current scarcity of resonance modes and low resonance ratio hamper the further improvements of NLO performance. Herein, we propose a new resonant channel of charge transfer (CT) excited states from metal halide polyhedra to organic ligand to boost the second-order optical nonlinearity of chiral HOMHs. The model lead halide (C7H10N)PbBr3 (C7H10N=1-ethylpyridinium) exhibits a drastically enhanced second harmonic generation in resonance to the deep CT exciton energy, with intensity of up to 111.0 times that of KDP and 10.9 times that of urea. The effective NLO coefficient has been determined to be as high as ~40.2 pm V-1, balanced with a large polarization ratio and high laser damage threshold. This work highlights the contribution of organic ligands in the construction of a resonant channel for enhancing second-order NLO coefficients of metal halides, and thus provides guidelines for designing new chiral HOMHs materials for advanced nonlinear photonic applications.

Modulating Dimensionality of 2D Perovskite Layers for Efficient and Stable 2D/3D Perovskite Photodetectors

Two-dimensional (2D) perovskites have been widely adopted for improving the performance and stability of three-dimensional (3D) metal halide perovskite devices. However, rational manipulation of the phase composition of 2D perovskites for suitable energy level alignment in 2D/3D perovskite photodetectors (PDs) has been rarely explored. Herein, we precisely controlled the dimensionality of the 2D perovskite on CsPbI2Br films by tuning the polarity of the n-butylammonium iodide (BAI)-based solvents. In comparison to the pure n = 1 2D perovskite (ACN-BAI) formed by acetonitrile treatment, a mixture of n = 1 and n = 2 phases (IPA-BAI) generated by isopropanol (IPA) treatment guaranteed more robust defect passivation and favorable energy level alignment at the perovskite/hole transport layer interface. Consequently, the IPA-BAI PD exhibited a responsivity of 0.41 A W-1, a detectivity of 1.01 × 1013 Jones, and a linear dynamic range of 120 dB. Furthermore, the mixed-phase 2D layer effectively shielded the 3D perovskite from moisture. The IPA-BAI device retained 76% of its initial responsivity after 500 h of nonencapsulated storage at 10% relative humidity. This research provides valuable insights into the dimensional modulation of 2D perovskites for further enhancing the performance of 2D/3D perovskite PDs.

Enhancing the performance of PbS:CsPbBr3 bulk-heterojunction photodetectors by treating with imidazolium-based ionic liquids

All-inorganic lead halide perovskites and quantum dots (QDs) have gained significant attention since their emergence, owing to their immense potential for applications in optoelectronic devices. Here, enhanced-performance broadband photodetectors based on the bulk-heterostructure of a CsPbBr3 perovskite and PbS colloidal quantum dots (CQDs) are presented, and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) ionic liquids as a dual-purpose additive were introduced in the blended film to regulate the surface of QDs by facilitating surface passivation, adjusting energy levels, and coupling with longer alkyl chains as compared to iodide ions (I-). As a result, a superior-quality bulk-heterostructure based photodetector with long-term stability was obtained, showing outstanding performance in photodetection across the visible to near-infrared wavelength range, demonstrating a high photoresponsivity of 22.4 A W-1 with a response time of 16.2 ms and a specific detectivity of 1.58 × 1014 Jones under 405 nm illumination. Thus, this work provides a novel modification strategy for PbS:CsPbBr3 as a promising material for novel optoelectronics.

Integration of One-Dimensional (1D) Lead-Free Perovskite Microbelts onto Silicon for Ultraviolet-Visible-Near-Infrared (UV-vis-NIR) Heterojunction Photodetectors

Lead-free perovskites are considered to be candidates for next-generation photodetectors, because of their excellent charge carrier transport properties and low toxicity. However, their application in integrated circuits is hindered by their inadequate performance and size restrictions. To aim at the development of lead-free perovskite-integrated optoelectronic devices, a CsAg2I3/silicon (CAI/Si) heterojunction is presented in this work by using a spatial confinement growth method, where the in-plane growth of CAI microbelts with high-quality single-crystal characteristics is primarily dependent on the concentration of surrounding precursor solution. The fabricated photodetectors based on the CAI/Si heterojunctions exhibit a broad-spectrum detection capability in the ultraviolet-visible-near-infrared (UV-vis-NIR) range. In addition, the photodetectors show good photoelectric detection performance, including a maximum responsivity of 48.5 mA/W and detectivity of 1.13 × 1011 Jones, respectively. Besides, the photodetectors have a rapid response of 6.5/224 μs and good air stability for over 2 months. This work contributes a new idea to design next-generation optoelectronic devices with high integration density.

Perovskite materials in X-ray detection and imaging: recent progress, challenges, and future prospects

Perovskite materials have attracted significant attention as innovative and efficient X-ray detectors owing to their unique properties compared to traditional X-ray detectors. Herein, chronologically, we present an in-depth analysis of X-ray detection technologies employing organic-inorganic hybrids (OIHs), all-inorganic and lead-free perovskite material-based single crystals (SCs), thin/thick films and wafers. Particularly, this review systematically scrutinizes the advancement of the diverse synthesis methods, structural modifications, and device architectures exploited to enhance the radiation sensing performance. In addition, a critical analysis of the crucial factors affecting the performance of the devices is also provided. Our findings revealed that the improvement from single crystallization techniques dominated the film and wafer growth techniques. The probable reason for this is that SC-based devices display a lower trap density, higher resistivity, large carrier mobility and lifetime compared to film- and wafer-based devices. Ultimately, devices with SCs showed outstanding sensitivity and the lowest detectable dose rate (LDDR). These results are superior to some traditional X-ray detectors such as amorphous selenium and CZT. In addition, the limited performance of film-based devices is attributed to the defect formation in the bulk film, surfaces, and grain boundaries. However, wafer-based devices showed the worst performance because of the formation of voids, which impede the movement of charge carriers. We also observed that by performing structural modification, various research groups achieved high-performance devices together with stability. Finally, by fusing the findings from diverse research works, we provide a valuable resource for researchers in the field of X-ray detection, imaging and materials science. Ultimately, this review will serve as a roadmap for directing the difficulties associated with perovskite materials in X-ray detection and imaging, proposing insights into the recent status, challenges, and promising directions for future research.

Fano-type discrete-continuum interaction in perovskites and its manifestation in Raman spectral line shapes

Fano resonance is one of the most significant physical phenomena that correlates microscopic processes with macroscopic manifestations for experimental observations using different spectroscopic techniques. Owing to its importance, a focused study is required to clearly understand the origin of certain modifications in spectral behaviour, the nature of which is different for different materials. This means that a careful understanding of Fano interactions can enhance the understanding of several technologically important materials, including perovskites, which are also important in the area of energy storage and conversion. In semiconductors and nano materials (including 2-D materials), Fano interactions occur due to the intervalence or interconduction band transitions. However, in perovskites, Fano interactions are dominated by the interaction between polar phonons or excitons with electronic continuum. Raman spectroscopy, being a sensitive and non-destructive tool, detects subtle scale phenomena, such as Fano interactions, by analysing the Raman line shape. Herein, different dimensions associated with the identification and thereafter the origin of the Fano resonance in perovskites, which are used in energy related areas, have been highlighted using Raman scattering.

Tunable Periodic Nanopillar Array for MAPbI3 Perovskite Photodetectors with Improved Light Absorption

In the field of optoelectronic applications, the vigorous development of organic-inorganic hybrid perovskite materials, such as methylammonium lead triiodide (MAPbI3), has spurred continuous research on methods to enhance the photodetection performance. Periodic nanoarrays can effectively improve the light absorption of perovskite thin films. However, there are still challenges in fabricating tunable periodic patterned and large-area perovskite nanoarrays. In this study, we present a cost-effective and facile approach utilizing nanosphere lithography and dry etching techniques to create a large-area Si nanopillar array, which is employed for patterning MAPbI3 thin films. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) results reveal that the introduction of nanopillar structures did not have a significant adverse effect on the crystallinity of the MAPbI3 thin film. Light absorption tests and optical simulations indicate that the nanopillar array enhances the light intensity within the perovskite films, leading to photodetectors with a responsivity of 11.2 A/W and a detectivity of 7.3 × 1010 Jones at 450 nm in wavelength. Compared with photodetectors without nanostructures, these photodetectors exhibit better visible light absorption. Finally, we demonstrate the application of these photodetector arrays in a prototype image sensor.

Circularly Polarized Light Emission from Nonchiral Perovskites Incorporated into Nanoporous Cholesteric Polymer Templates

Chiral perovskites have garnered significant attention, owing to their chiroptical properties and emerging applications. Current fabrication methods often involve complex chemical synthesis routes. Herein, an alternative approach for introducing chirality into nonchiral hybrid organic-inorganic perovskites (HOIPs) using nanotemplates composed of cholesteric polymeric networks is proposed. This method eliminates the need for additional molecular design. In this process, HOIP precursors are incorporated into a porous cholesteric polymer film, and two-dimensional (2D) HOIPs grow inside the nanopores. Circularly polarized light emission (CPLE) was observed even though the selective reflection band of the cholesteric polymer films containing a representative HOIP deviated from the emission wavelength of the 2D HOIP. This effect was confirmed by the induced circular dichroism (CD) observed in the absorbance band of the HOIP. The observed CPLE and CD are attributed to the chirality induced by the template in the originally nonchiral 2D HOIP. Additionally, the developed 2D HOIP exhibited a long exciton lifetime and good stability under harsh conditions. These findings provide valuable insights into the development and design of innovative optoelectronic materials.

Phase-engineering compact and flexible CsPbBr3 microcrystal films for robust X-ray detection

All-inorganic CsPbBr3 perovskites have gained significant attention due to their potential in direct X-ray detection. The fabrication of stable, pinhole-free thick films remains challenging, hindering their integration in durable, large-area high-resolution devices. In this study, we propose a facile strategy using a non-conductive polymer to create a flexible, compact thick film under ambient conditions. Furthermore, we investigate the effect of introducing the 2D CsPb2Br5 phase into CsPbBr3 perovskite crystals on their photophysical properties and charge transport. Upon X-ray exposure, the devices consisting of the dual phase exhibit improved stability and more effective operation at higher voltages. Rietveld refinement shows that, due to the presence of the second phase, local distortions and Pb-vacancies are introduced within the CsPbBr3 lattice. This in turn presumably increases the ion migration energy barrier, resulting in a very low dark current and hence, enhanced stability. This feature might benefit local charge extraction and, ultimately, the X-ray image resolution. These findings also suggest that introducing a second phase in the perovskite structure can be advantageous for efficient photon-to-charge carrier conversion, as applied in medical imaging.

Free Halogen Substitution of Chiral Hybrid Metal Halides for Activating the Linear and Nonlinear Chiroptical Properties

Halogen substitution has been proven as an effective approach to the band gap engineering and optoelectronic modulation of organic-inorganic hybrid metal halide (OIHMH) materials. Various high-performance mixed halide OIHMH film materials have been primarily obtained through the substitution of coordinated halogens in their inorganic octahedra. Herein, we propose a new strategy of substitution of free halogen outside the inorganic octahedra for constructing mixed halide OIHMH single crystals with chiral structures, resulting in a boost of their linear and nonlinear chiroptical properties. The substitution from DMA4[InCl6]Cl (DMA = dimethylammonium) to DMA4[InCl6]Br crystals through a facile antisolvent vaporization method produces centimeter-scale single crystals with high thermal stability along with high quantum yield photoluminescence, conspicuous circularly polarized luminescence, and greatly enhanced second harmonic generation (SHG). In particular, the obtained DMA4[InCl6]Br single crystal features an intrinsic chiral structure, exhibiting a significant SHG circular dichroism (SHG-CD) response with a highest reported anisotropy factor (gSHG-CD) of 1.56 among chiral OIHMH materials. The enhancements in both linear and nonlinear chiroptical properties are directly attributed to the modulation of octahedral distortion. The mixed halide OIHMH single crystals obtained by free halogen substitution confine the introduced halogens within free halogen sites of the lattice, thereby ensuring the stability of compositions and properties. The successful employment of such a free halogen substitution approach may broaden the horizon of the regulation of structures and the optoelectronic properties of the OIHMH materials.

High-sensitivity self-powered photodetector based on an in-situ prepared CsPbBr3 microwire/InGaN heterojunction

Low-dimensional CsPbBr3 perovskite materials have gained widespread attention, derived from their remarkable properties and potential for numerous optoelectronic applications. Herein, the sample of CsPbBr3 microwires were prepared horizontally onto n-type InGaN film substrate using an in-plane solution growth method. The resulting CsPbBr3 microwire/InGaN heterojunction allows for the achievement of a highly sensitive and broadband photodetector. Particularly for the implementation in a self-supplying manner, the best-performing photodetector can achieve a superior On/Off ratio of 4.6×105, the largest responsivity ∼ 800.0 mA/W, a maximum detectivity surpassing 4.6× 1012 Jones, and a high external quantum efficiency approaching 86.5% upon 405 nm light illumination. A rapid response time (∼ 4.48 ms/7.68 ms) was also achieved. The as-designed CsPbBr3 microwire/InGaN heterojunction device without any encapsulation exhibits superior comprehensive stability. Besides, the device featuring as a single pixel imaging unit can readily detect simple images under broadband light illumination with a high spatial resolution, acknowledging its outstanding imaging capability. The robust photodetection properties could be derived from the intense absorption of CsPbBr3 MWs and high-efficiency charge carriers transporting toward the in-situ formed CsPbBr3/InGaN heterointerface. The results may offer an available strategy for the in-situ construction of best-performing low-dimensional perovskite heterojunction optoelectronic devices.

Stabilizing Metal Halide Perovskites for Solar Fuel Production: Challenges, Solutions, and Future Prospects

Metal halide perovskites (MHPs) are emerging photocatalyst materials that can enable sustainable solar-to-chemical energy conversion by virtue of their broad absorption spectra, effective separation/transport of photogenerated carriers, and solution processability. Although preliminary studies show the excellent photocatalytic activities of MHPs, their intrinsic structural instability due to the low formation energy and soft ionic nature is an open challenge for their practical applications. This review discusses the latest understanding of the stability issue and strategies to overcome this issue for MHP-based photocatalysis. First, the origin of the instability issue at atomic levels and the design rules for robust structures are analyzed and elucidated. This is then followed by presenting several different material design strategies for stability enhancement, including reaction medium modification, material surface protection, structural dimensionality engineering, and chemical composition engineering. Emphases are placed on understanding the effects of these strategies on photocatalytic stability as well as the possible structure-performance correlation. Finally, the possible future research directions for pursuing stable and efficient MHP photocatalysts in order to accelerate their technological maturity on a practical scale are outlined. With that, it is hoped to provide readers a valuable snapshot of this rapidly developing and exciting field.

A Self-Powered UV Photodetector With Ultrahigh Responsivity Based on 2D Perovskite Ferroelectric Films With Mixed Spacer Cations

Self-powered photodetectors (PDs) have the advantages of no external power requirement, wireless operation, and long life. Spontaneous ferroelectric polarizations can significantly increase built-in electric field intensity, showing great potential in self-powered photodetection. Moreover, ferroelectrics possess pyroelectric and piezoelectric properties, beneficial for enhancing self-powered PDs. 2D metal halide perovskites (MHPs), which have ferroelectric properties, are suitable for fabricating high-performance self-powered PDs. However, the research on 2D metal halide perovskites ferroelectrics focuses on growing bulk crystals. Herein, 2D ferroelectric perovskite films with mixed spacer cations for self-powered PDs are demonstrated by mixing Ruddlesden-Popper (RP)-type and Dion-Jacobson (DJ)-type perovskite. The (BDA0.7 (BA2 )0.3 )(EA)2 Pb3 Br10 film possesses, overall, the best film qualities with the best crystalline quality, lowest trap density, good phase purity, and obvious ferroelectricity. Based on the ferro-pyro-phototronic effect, the PD at 360 nm exhibits excellent photoelectric properties, with an ultrahigh peak responsivity greater than 93 A W-1 and a detectivity of 2.5 × 1015 Jones, together with excellent reproducibility and stability. The maximum responsivities can be modulated by piezo-phototronic effect with an effective enhancement ratio of 480%. This work will open up a new route of designing MHP ferroelectric films for high-performance PDs and offers the opportunity to utilize it for various optoelectronics applications.

Spin Texture Sensitive Photodetection by Dion-Jacobson Tin Halide Perovskites

The organic spacer molecule is known to regulate the optoelectronic properties of two-dimensional (2D) perovskites. We show that the spacer layer thickness determines the nature of optical transitions, direct or indirect, by controlling the structural properties of the inorganic layer. The spin-orbit interactions lead to different electron spin orientations for the states associated with the conduction band minimum (CBM) and the valence band maximum (VBM). This leads to a direct as well as an indirect component of the transitions, despite them being direct in momentum space. The shorter chains have a larger direct component, leading to a better optoelectronic performance. The mixed halide Sn2+ Dion-Jacobson (DJ) perovskite with the shortest 4-C diammonium spacer outshines the photodetection parameters of those having longer (6-C and 8-C) spacers and the corresponding Ruddlesden-Popper (RP) phases. The DJ system with a 4-C spacer and equimolar Br/I embodies an unprecedentedly high responsivity of 78.1 A W-1 under 3 V potential bias at 485 nm wavelength, among the DJ perovskites. Without any potential bias, this phase manifests the self-powered photodetection parameters of 0.085 A W-1 and 9.9 × 1010 jones. The unusual role of electron spin texture in these high-performance photodetectors of the lead-free DJ perovskites provides an avenue to exploit the information coded in spins for semiconductor devices without any ferromagnetic supplement or magnetic field.

Bifunctional Interface Passivation via Copper Acetylacetonate for Efficient and Stable Perovskite Solar Cells

Manipulating interface defects can minimize interfacial nonradiative recombination, thus increasing the stability and performance of perovskite solar cells (PSCs). Here, copper acetylacetonate [Cu(acac)2] as a passivator is used to treat the interface between Spiro-OMeTAD and perovskite. Owing to the strong chelation, the uncoordinated Pb2+ could react with -C═O/-COH functional groups, firmly anchoring acetylacetonate at this interface or the grain boundaries (GBs) of perovskite films to construct multiple ligand bridges, accompanied by the p-type copper iodide formation with copper substituting lead. Simultaneously, Cu+-Cu2+ pairs transfer electrons from Pb0 to I0, suppressing deep level defects of Pb0 and I0 near the perovskite interface. These can be beneficial to hole-transferring. Moreover, the Schiff base complexes with hydrophobicity, from the reaction of acetylacetonate with perovskite, can lead to tightly packed adjacent perovskite surfaces and self-seal the GBs of the perovskite, inhibiting moisture diffusion for long-term stability. Consequently, the Cu(acac)2-based PSC has achieved more than 24% champion efficiency while retaining ca. 92% of the initial power conversion efficiency after 1680 h of storage.

Synthesis of CsPbBr3 in Micro Total Reaction System: Fast Operation Space Mapping and Subsecond Growth Process Monitoring

Lead halide perovskite nanocrystals (LHP NCs) have the characteristics of fast reaction kinetics and crystal instability due to the intrinsically highly ionic bonding between the respective ions, which bring challenges for revealing the growth kinetics and practical applications. Compared with conventional batch synthesis methods, the single-function microreactor can achieve precise and stable control of the NCs synthesis process, but it still has the shortcoming of not being able to obtain information about the growth process. In this study, a micro Total Reaction System (μTRS) with remote control, online detection, and rapid data analysis functions is designed. μTRS can sample the photoluminescence information of CsPbBr3 NCs growth in ligand-assisted reprecipitation method. CsPbBr3 NCs with an emission range of 435-492 nm are successfully detected, which breaks the record of the smallest size of CsPbBr3 NCs synthesized directly from precursors. The real-time feature of μTRS enables the construction of an automated close-loop synthesis system. Besides, the rapid acquisition and timely processing of product information enable the rapid mapping of the operation space for CsPbBr3 NCs preparation, which provides a reliable and learnable data set for designing a fully autonomous microreaction system capable of synthesizing NCs.

Tricolor narrowband planar perovskite photodetectors based on FP microcavity structure

This paper presents a novel tunable narrowband photodetector based on Ag-MgF2-Ag (metal-dielectric-metal: MDM) Fabry-Perot (FP) microcavity structure. The tunability is achieved through precise adjustment of the thickness of the metal and intermediate dielectric layers of the FP microcavity, taking into account the response spectral range of planar perovskite. After optimizing the parameters mentioned above, the prototype devices were prepared by combining the perovskite layer and MDM layer. The center wavelength of the planar detector can be tuned from 430 nm to 680 nm within the detection band of 400-800 nm, with a narrow FWHM about 30 nm and a relatively high response of 0.05 A/W @ 5 V bias voltage for 500 nm. Meanwhile the rise and fall times of the detector are 375 ms and 550 ms, respectively. The experimental results are corroborated by the theory. Our design is highly beneficial to such applications as hyperspectral photography and color-related active optical devices, which paves the way to design this kind of triple structure.

Facile Vertical Structure Broadband Photodetectors Enabled by Polyvinylpyrrolidone-Regulated Perovskite and Near-Infrared-Sensitive Lead Phthalocyanine

Broadband photodetectors have drawn tremendous attention in many application areas such as imaging, optical communication, and biochemical sensing. Perovskite is a star material with broad spectral absorption, but it is challenging to develop ultraviolet-visible-near-infrared (UV-Vis-NIR) ultra-broadband photodetectors due to the insufficient absorption in the near-infrared region. Moreover, it is difficult to construct a diode-type photodetector with a simple vertical structure based only on perovskite materials. Here, facile vertical structure broadband photodetectors were fabricated based on heterojunctions that were composed of perovskite MAPbI3 films with UV-Vis absorption spectrum and small organic molecule lead phthalocyanine (PbPc) with strong NIR optical absorption, resulting in UV-Vis-NIR ultra-broadband photodetection. The quality of MAPbI3 films was improved by introducing polyvinylpyrrolidone (PVP) modification, and subsequently, the corresponding MAPbI3/PbPc heterojunction-based photodetectors exhibited rectification characteristics and reduced reverse dark currents. When the PVP mass ratio is 1 wt%, the photodetector achieved the best performance that the spectral response uniformity factor was as high as 0.77, the photoresponsivity exceeded 10 A/W, and the photoresponse time was less than 0.5 ms under a light intensity of 0.013 mW/cm2 in the UV-Vis to NIR spectral range. These results are comparable or superior to those of some inorganic, organic, and perovskite photodetectors reported previously. This study would provide an effective strategy to construct high-performance perovskite photodetectors based on a simple vertical structure, paving the way to the realization of UV-Vis-NIR broadband photodetection.

Ultraviolet-Visible-Short-Wavelength Infrared Broadband and Fast-Response Photodetectors Enabled by Individual Monocrystalline Perovskite Nanoplate

Perovskite-based photodetectors exhibit potential applications in communication, neuromorphic chips, and biomedical imaging due to their outstanding photoelectric properties and facile manufacturability. However, few of perovskite-based photodetectors focus on ultraviolet-visible-short-wavelength infrared (UV-Vis-SWIR) broadband photodetection because of the relatively large bandgap. Moreover, such broadband photodetectors with individual nanocrystal channel featuring monolithic integration with functional electronic/optical components have hardly been explored. Herein, an individual monocrystalline MAPbBr3 nanoplate-based photodetector is demonstrated that simultaneously achieves efficient UV-Vis-SWIR detection and fast-response. Nanoplate photodetectors (NPDs) are prepared by assembling single nanoplate on adjacent gold electrodes. NPDs exhibit high external quantum efficiency (EQE) and detectivity of 1200% and 5.37 × 1012 Jones, as well as fast response with rise time of 80 µs. Notably, NPDs simultaneously achieve high EQE and fast response, exceeding most perovskite devices with multi-nanocrystal channel. Benefiting from the high specific surface area of nanoplate with surface-trap-assisted absorption, NPDs achieve high performance in the near-infrared and SWIR spectral region of 850-1450 nm. Unencapsulated devices show outstanding UV-laser-irradiation endurance and decent periodicity and repeatability after 29-day-storage in atmospheric environment. Finally, imaging applications are demonstrated. This work verifies the potential of perovskite-based broadband photodetection, and stimulates the monolithic integration of various perovskite-based devices.

Multifunctional Perovskite Photodetectors: From Molecular-Scale Crystal Structure Design to Micro/Nano-scale Morphology Manipulation

Multifunctional photodetectors boost the development of traditional optical communication technology and emerging artificial intelligence fields, such as robotics and autonomous driving. However, the current implementation of multifunctional detectors is based on the physical combination of optical lenses, gratings, and multiple photodetectors, the large size and its complex structure hinder the miniaturization, lightweight, and integration of devices. In contrast, perovskite materials have achieved remarkable progress in the field of multifunctional photodetectors due to their diverse crystal structures, simple morphology manipulation, and excellent optoelectronic properties. In this review, we first overview the crystal structures and morphology manipulation techniques of perovskite materials and then summarize the working mechanism and performance parameters of multifunctional photodetectors. Furthermore, the fabrication strategies of multifunctional perovskite photodetectors and their advancements are highlighted, including polarized light detection, spectral detection, angle-sensing detection, and self-powered detection. Finally, the existing problems of multifunctional detectors and the perspectives of their future development are presented.

Advances in the Application of Perovskite Materials

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

New Dication-Based Lead-Deficient 3D MAPbI3 and FAPbI3 "d-HPs" Perovskites with Enhanced Stability

Toxicity induced by the presence of lead and the rather poor stability of halide perovskite semiconductors represent the major issues for their large-scale application. We previously reported a new family of lead- and iodide-deficient MAPbI₃ and FAPbI₃ perovskites called d-HPs (for lead- and iodide-deficient halide perovskites) based on two organic cations: hydroxyethylammonium HO-(CH₂)₂-NH₃⁺ (HEA⁺) and thioethylammonium HS-(CH₂)₂-NH₃⁺ (TEA⁺). In this article, we report the use of an organic dication, 2-hydroxypropane-1,3-diaminium (2-propanol 1,3 diammonium), named PDA²⁺, to create new 3D d-HPs based on the MAPbI₃ and FAPbI₃ network with general formulations of (PDA)_0,88x(MA)_1-0,76x[Pb_1-xI_3-x] and (PDA)_1,11x(FA)_1-1,22x[Pb_1-xI_3-x], respectively. These d-HPs have been successfully synthesized as crystals, powders, and thin films and exhibit improved air stability compared to their reference MAPbI₃ and FAPbI₃ perovskite counterparts. PDA²⁺-based deficient MAPbI₃ was also tested in operational perovskite solar cells and exhibited an efficiency of 13.0% with enhanced stability.

2D/3D Perovskite Photodetectors with High Response Frequency and Improved Stability Based on Thiophene-2-ethylamine and Dual Additives

Organic-inorganic lead halide perovskite materials have received great attention in recent years. However, the poor stability of these materials severely limits the commercial application of perovskite devices. Here, we used thiophene-2-ethylammonium iodide (TEAI) material as the organic spacer NH₄SCN and NH₄Cl as the dual additives to realize high-stability two-dimensional (2D)/three-dimensional (3D) perovskite thin films for perovskite photodetectors. Then, we investigated different effects of the dual additives on the orientation and crystallinity of the perovskite films. At room temperature, the optimized 2D/3D perovskite photodetectors exhibit good performance with high external quantum efficiency (EQE) (72%), large responsivity (0.36 A/W), high detectivity (2.46 × 10¹² Jones at the bias of 0 V), high response frequency (1.7 MHz), and improved stability (retains 90% photocurrent after 2000 h storage in RT and 10% RH conditions). Based on these devices, a dual-channel optical transport system and a light-intensity adder are achieved. The results of this study indicate that, with a simple process, the TEAI and dual-additives based 2D/3D perovskite photodetectors have promising applications in light-intensity adder and optical communication systems.

A2Bn-1PbnI3n+1 (A = BA, PEA; B = MA; n = 1, 2): Engineering Quantum-Well Crystals for High Mass Density and Fast Scintillators

Quantum-well (QW) hybrid organic-inorganic perovskite (HOIP) crystals, e.g., A₂PbX₄ (A = BA, PEA; X = Br, I), demonstrated significant potentials as scintillating materials for wide energy radiation detection compared to their individual three-dimensional (3D) counterparts, e.g., BPbX₃ (B = MA). Inserting 3D into QW structures resulted in new structures, namely A₂BPb₂X₇ perovskite crystals, and they may have promising optical and scintillation properties toward higher mass density and fast timing scintillators. In this article, we investigate the crystal structure as well as optical and scintillation properties of iodide-based QW HOIP crystals, A₂PbI₄ and A₂MAPb₂I₇. A₂PbI₄ crystals exhibit green and red emission with the fastest PL decay time <1 ns, while A₂MAPb₂I₇ crystals exhibit a high mass density of >3.0 g/cm³ and tunable smaller bandgaps <2.1 eV resulting from quantum and dielectric confinement. We observe that A₂PbI₄ and PEA₂MAPb₂I₇ show emission under X- and γ-ray excitations. We further observe that some QW HOIP iodide scintillators exhibit shorter radiation absorption lengths (∼3 cm at 511 keV) and faster scintillation decay time components (∼0.5 ns) compared to those of QW HOIP bromide scintillators. Finally, we investigate the light yields of iodide-based QW HOIP crystals at 10 K (∼10 photons/keV), while at room temperature they still show pulse height spectra with light yields between 1 and 2 photons/keV, which is still >5 times lower than those for bromides. The lower light yields can be the drawbacks of iodide-based QW HOIP scintillators, but the promising high mass density and decay time results of our study can provide the right pathway for further improvements toward fast-timing applications.

Flexible All-Inorganic Perovskite Photodetector with a Combined Soft-Hard Layer Produced by Ligand Cross-Linking

Although perovskite nanocrystals have attracted considerable interests as emerging semiconductors in optoelectronic devices, design and fabrication of a deformable structure with high stability and flexibility while meeting the charge transport requirements remain a huge challenge. Herein, a combined soft-hard strategy is demonstrated to fabricate intrinsically flexible all-inorganic perovskite layers for photodetection via ligand cross-linking. Perfluorodecyltrichlorosilane (FDTS) is employed as the capping ligand and passivating agent bound to the CsPbBr₃ surface via Pb-F and Br-F interactions. The SiCl head groups of FDTS are hydrolyzed to produce SiOH groups which subsequently condense to form the SiOSi network. The CsPbBr₃ @FDTS nanocrystals (NCs) are monodispersed cubes with an average particle size of 13.03 nm and exhibit excellent optical stability. Furthermore, the residual hydroxyl groups on the surface of the CsPbBr₃ @FDTS render the NCs tightly packed and cross-linked to each other to form a dense and elastic CsPbBr₃ @FDTS film with soft and hard components. The photodetector based on the flexible CsPbBr₃ @FDTS film exhibits outstanding mechanical flexibility and robust stability after 5000 bending cycles.

Pinhole-free 2D Ruddlesden-Popper perovskite layer with close packed large crystalline grains, suitable for optoelectronic applications

Here, we achieved pinhole-free 2D Ruddlesden-Popper Perovskite (RPP) BA₂PbI₄ layers with close packed crystalline grains with dimension of about 30 × 30 µm², which have been demonstrated to be favorable for optoelectronic applications, such as fast response RPP-based metal/semiconductor/metal photodetectors. We explored affecting parameters in hot casting of BA₂PbI₄ layers, and proved that oxygen plasma treatment prior to hot casting plays a significant role to achieve high quality close packed polycrystalline RPP layers at lower hot cast temperatures. Moreover, we demonstrate that crystal growth of 2D BA₂PbI₄ can be dominantly controlled by the rate of solvent evaporation through substrate temperature or rotational speed, while molarity of the prepared RPP/DMF precursor is the dominant factor that determines the RPP layer thickness, and can affect the spectral response of the realized photodetector. Benefiting from the high light absorption and inherent chemical stability of 2D RPP layers, we achieved high responsivity and stability, and fast response photodetection from perovskite active layer. We achieved a fast photoresponse with rise and fall times of 189 µs and 300 µs, and the maximum responsivity of 119 mA/W and detectivity of 2.15 × 10⁸ Jones in response to illumination wavelength of 450 nm. The presented polycrystalline RPP-based photodetector benefits from a simple and low-cost fabrication process, suitable for large area production on glass substrate, a good stability and responsivity, and a promising fast photoresponse, even around that of exfoliated single crystal RPP-based counterparts. However, it is well known that exfoliation methods suffer from poor repeatability and scalability, which make them incompatible with mass production and large area applications.

Real-time observation of ion exchange dynamics during surface treatment of all-inorganic perovskite quantum dots with Zn-halogenide complexes for color tuning and enhanced quantum efficiency

All-inorganic lead perovskite quantum dots (QDs), due to their distinctive optical properties, have become one of the "hottest" topics in materials science; therefore, the development of new QD synthesis methods or their emission color adjustment is of great interest. Within this study, we present the simple preparation of QDs employing a novel ultrasound-induced hot-injection method, which significantly reduces the QD synthesis time from several hours to merely 15-20 minutes. Moreover, the post-synthesis treatment of perovskite QDs in solutions using zinc halogenide complexes could increase the QD emission intensity and, at the same time, boost their quantum efficiency. This behavior is due to the zinc halogenide complex's ability to remove or significantly reduce the number of surface electron traps in perovskite QDs. Finally, the experiment that shows the ability to instantly adjust the desired emission color of perovskite QDs by variation of the amount of added zinc halogenide complex is presented. The instantly obtained perovskite QD colors cover virtually the full range of the visible spectrum. The zinc halogenide modified perovskite QDs exhibit up to 10-15% higher QEs than those prepared by an individual synthesis.

Self-Powered Bipolar Photodetector Based on a Ce-BaTiO3 PTCR Semiconductor for Logic Gates

Ferroelectric materials bring new opportunities for self-powdered photodetectors, taking advantage of their anomalous bulk photovoltaic effect. However, ferroelectric-based photodetectors suffer from relatively poor responsivity and detectivity due to obstacles of low electrical conductivity and low photoelectric conversion ability. The present work proposes a strategy based on heterovalent ion Ce-doping into BaTiO₃ (Ce-BTO) that gives rise to a good room temperature conductivity combined with a significant PTCR (positive temperature coefficient of resistivity) effect. By utilizing a Ce-BTO PTCR semiconductor, a high-performance self-powered photodetector ITO/Ce-BTO/Ag is fabricated, demonstrating a polarity-switchable photoresponse with the change of wavelength due to the competition between hot electrons induced by the Ag plasmonic effect and electron-hole pairs separated by a Schottky barrier. Moreover, benefiting from the reduced bandgap and the introduced impurity states, good responsivity (9.85 × 10^-5 A/W) and detectivity (1.25 × 10¹⁰ Jones) as well as fast response/recovery time (83/47 ms) is achieved under 450 nm illumination. Finally, four representative logic gates ("OR", "AND", "NOR", and "NAND") are demonstrated with one photodetector via the bipolar photoresponse. This work opens an avenue to promote the application of PTCR semiconductors in optoelectronics, offering a conceivable means toward high-performance self-powered photodetectors.

Visible Near-Infrared Photodetection Based on Ta2NiSe5/WSe2 van der Waals Heterostructures

The increasing interest in two-dimensional materials with unique crystal structures and novel band characteristics has provided numerous new strategies and paradigms in the field of photodetection. However, as the demand for wide-spectrum detection increases, the size of integrated systems and the limitations of mission modules pose significant challenges to existing devices. In this paper, we present a van der Waals heterostructure photodetector based on Ta₂NiSe₅/WSe₂, leveraging the inherent characteristics of heterostructures. Our results demonstrate that this detector exhibits excellent broad-spectrum detection ability from the visible to the infrared bands at room temperature, achieving an extremely high on/off ratio, without the need for an external bias voltage. Furthermore, compared to a pure material detector, it exhibits a fast response and low dark currents (~3.6 pA), with rise and fall times of 278 μs and 283 μs for the response rate, respectively. Our findings provide a promising method for wide-spectrum detection and enrich the diversity of room-temperature photoelectric detection.

Retina-inspired narrowband perovskite sensor array for panchromatic imaging

The retina is the essential part of the human visual system that receives light, converts it to neural signal, and transmits to brain for visual recognition. The red, green, and blue (R/G/B) cone retina cells are natural narrowband photodetectors (PDs) sensitive to R/G/B lights. Connecting with these cone cells, a multilayer neuro-network in the retina provides neuromorphic preprocessing before transmitting to brain. Inspired by this sophistication, we develop the narrowband (NB) imaging sensor combining R/G/B perovskite NB sensor array (mimicking the R/G/B photoreceptors) with a neuromorphic algorithm (mimicking the intermediate neural network) for high-fidelity panchromatic imaging. Compared to commercial sensors, we use perovskite "intrinsic" NB PD to exempt the complex optical filter array. In addition, we use an asymmetric device configuration to collect photocurrent without external bias, enabling a power-free photodetection feature. These results display a promising design for efficient and intelligent panchromatic imaging.

Exploring Solar Cells Based on Lead- and Iodide-Deficient Halide Perovskite (d-HP) Thin Films

Perovskite solar cells have become more and more attractive and competitive. However, their toxicity induced by the presence of lead and their rather low stability hinders their potential and future commercialization. Reducing lead content while improving stability then appears as a major axis of development. In the last years, we have reported a new family of perovskite presenting PbI⁺ unit vacancies inside the lattice caused by the insertion of big organic cations that do not respect the Goldschmidt tolerance factor: hydroxyethylammonium HO-(CH₂)₂-NH₃⁺ (HEA⁺) and thioethylammonium HS-(CH₂)₂-NH₃⁺ (TEA⁺). These perovskites, named d-HPs for lead and halide-deficient perovskites, present a 3D perovskite corner-shared Pb_1-xI_3-x network that can be assimilated to a lead-iodide-deficient MAPbI₃ or FAPbI₃ network. Here, we propose the chemical engineering of both systems for solar cell optimization. For d-MAPbI₃-HEA, the power conversion efficiency (PCE) reached 11.47% while displaying enhanced stability and reduced lead content of 13% compared to MAPbI₃. On the other hand, d-FAPbI₃-TEA delivered a PCE of 8.33% with astounding perovskite film stability compared to classic α-FAPI. The presence of TEA⁺ within the lattice impedes α-FAPI degradation into yellow δ-FAPbI₃ by direct degradation into inactive Pb(OH)I, thus dramatically slowing the aging of d-FAPbI₃-TEA perovskite.

Highly Sensitive Tin-Lead Perovskite Photodetectors with Over 450 Days Stability Enabled by Synergistic Engineering for Pulse Oximetry System

Low-bandgap tin (Sn)-lead (Pb) halide perovskites can achieve near-infrared response for photodetectors. However, the Sn-based devices suffer from notorious instability and high defect densities due to the oxidation propensity of Sn²⁺ . Herein, a multifunctional additive 4-amino-2,3,5,6-tetrafluorobenzoic acid (ATFBA) is presented, which can passivate surface defects and inhibit the oxidation of Sn²⁺ through hydrogen bonds and chelation coordination from the terminal amino and carboxyl groups. The perfluorinated benzene ring structure of ATFBA affords the passivator assembled at the grain boundaries to enhance the water resistance. With the synergistical passivation of these functional groups, the Sn-Pb perovskite photodetector exhibits a remarkable responsivity of 0.52 A W^-1 and an excellent specific detectivity of 5.34 × 10¹² Jones at 850 nm, along with remaining 97% of its initial responsivity over 450 days. Benefitting from high sensitivity, the photodetector is integrated into a pulse oximetry sensor visualization system, yielding accurate blood oxygen saturation and heart rate with less than 2% error. This work paves the avenue toward constructing high-performance and stable Sn-Pb perovskite photodetectors for practical applications.

Ligands in Lead Halide Perovskite Nanocrystals: From Synthesis to Optoelectronic Applications

Ligands are indispensable for perovskite nanocrystals (NCs) throughout the whole lifetime, as they not only play key roles in the controllable synthesis of NCs with different sizes and shapes, but also act as capping shell that affects optical properties and electrical coupling of NCs. Establishing a systematic understanding of the relationship between ligands and perovskite NCs is significant to enable many potential applications of NCs. This review mainly focuses on the influence of ligands on perovskite NCs. First of all, the ligands-dominated size and shape control of NCs is discussed. Whereafter, the surface defects of NCs and the bonding between ligands and perovskite NCs are classified, and corresponding post-treatment of surface defects via ligands is also summarized. Furthermore, advances in engineering the ligands towards the high performance of optoelectronic devices based on perovskite NCs, including photodetector, solar cell, light emitting diode (LED), and laser, and finally to potential challenges are also discussed.

Hybrid mixed-dimensional WTe2/CsPbI3perovskite heterojunction for high-performance photodetectors

Perovskites have showed significant potential for the application in photodetectors due to their outstanding electrical and optical properties. Integrating two-dimensional (2D) materials with perovskites can make full use of the high carrier mobility of 2D materials and strong light absorption of perovskite to realize excellent optoelectrical properties. Here, we demonstrate a photodetector based on the WTe₂/CsPbI₃heterostructure. The quenching and the shortened lifetime of photoluminescence (PL) for CsPbI₃perovskite confirms the efficient charge transfer at the WTe₂/CsPbI₃heterojunction. After coupled with WTe₂, the photoresponsivity of the CsPbI₃photodetector is improved by almost two orders of magnitude due to the high-gain photogating effect. The WTe₂/CsPbI₃heterojunction photodetector reveals a large responsivity of 1157 A W^-1and a high detectivity of 2.1 × 10¹³Jones. The results pave the way for the development of high-performance optoelectronic devices based on 2D materials/perovskite heterojunctions.

A nickel(ii)-based one-dimensional organic-inorganic halide perovskite ferroelectric with the highest Curie temperature

Organic-inorganic halide perovskites (OIHPs) are very eye-catching due to their chemical tunability and rich physical properties such as ferroelectricity, magnetism, photovoltaic properties and photoluminescence. However, no nickel-based OIHP ferroelectrics have been reported so far. Here, we designed an ABX₃ OIHP ferroelectric (3-pyrrolinium)NiCl₃, where the 3-pyrrolinium cations are located on the voids surrounded by one-dimensional chains composed of NiCl₆-face-sharing octahedra via hydrogen bonding interactions. Such a unique structure enables the (3-pyrrolinium)NiCl₃ with a high spontaneous polarization (P _s) of 5.8 μC cm^-2 and a high Curie temperature (T _c) of 428 K, realizing dramatic enhancement of 112 and 52 K compared to its isostructural (3-pyrrolinium)MCl₃ (M = Cd, Mn). To our knowledge, remarkably, (3-pyrrolinium)NiCl₃ should be the first case of nickel(ii)-based OIHP ferroelectric to date, and its T _c of 428 K (35 K above that of BaTiO₃) is the highest among all reported one-dimensional OIHP ferroelectrics. This work offers a new structural building block for enriching the family of OIHP structures and will inspire the further exploration of new nickel(ii)-based OIHP ferroelectrics.

Graphene oxide:Fe2O3 nanocomposites for photodetector applications: experimental and ab initio density functional theory study

In this report, a GO:Fe₂O₃ nanocomposite was synthesized using a one-step covalent attachment approach using a sol-gel technique. The optical absorbance, photoconductive, photo-capacitive, and electrical properties were obtained using spectroscopy, and current-voltage (I-V) measurements. An enhanced optical absorbance with corresponding band gap reduction is observed when Fe₂O₃ nanoparticles are incorporated in GO. A corresponding enhanced photoconductance in the order of ×10¹ was observed due to the impact of band gap narrowing. The enhanced photoconductivity and photo-capacitance can be attributed to energy and charge transfer between GO and Fe atoms, leading to the generation of photo-induced excitons. Density function theory calculations indicate increased charge transfer when GO is doped with Fe-O atoms, which is consistent with experimental data. The observed results could potentially enable the use of GO:Fe₂O₃ nanocomposites for photodetectors and other optoelectronic applications.

Recent Development of Halide Perovskite Materials and Devices for Ionizing Radiation Detection

Ionizing radiation such as X-rays and γ-rays has been extensively studied and used in various fields such as medical imaging, radiographic nondestructive testing, nuclear defense, homeland security, and scientific research. Therefore, the detection of such high-energy radiation with high-sensitivity and low-cost-based materials and devices is highly important and desirable. Halide perovskites have emerged as promising candidates for radiation detection due to the large light absorption coefficient, large resistivity, low leakage current, high mobility, and simplicity in synthesis and processing as compared with commercial silicon (Si) and amorphous selenium (a-Se). In this review, we provide an extensive overview of current progress in terms of materials development and corresponding device architectures for radiation detection. We discuss the properties of a plethora of reported compounds involving organic-inorganic hybrid, all-inorganic, all-organic perovskite and antiperovskite structures, as well as the continuous breakthroughs in device architectures, performance, and environmental stability. We focus on the critical advancements of the field in the past few years and we provide valuable insight for the development of next-generation materials and devices for radiation detection and imaging applications.

Metal Halide Perovskite Nanowires: Controllable Synthesis, Mechanism, and Application in Optoelectronic Devices

Metal halide perovskites are promising energy materials because of their high absorption coefficients, long carrier lifetimes, strong photoluminescence, and low cost. Low-dimensional halide perovskites, especially one-dimensional (1D) halide perovskite nanowires (NWs), have become a hot research topic in optoelectronics owing to their excellent optoelectronic properties. Herein, we review the synthetic strategies and mechanisms of halide perovskite NWs in recent years, such as hot injection, vapor phase growth, selfassembly, and solvothermal synthesis. Furthermore, we summarize their applications in optoelectronics, including lasers, photodetectors, and solar cells. Finally, we propose possible perspectives for the development of halide perovskite NWs.

Effect of Interface Modification on Mechanoluminescence-Inorganic Perovskite Impact Sensors

It is becoming increasingly important to develop innovative self-powered, low-cost, and flexible sensors with the potential for structural health monitoring (SHM) applications. The mechanoluminescence (ML)-perovskite sensor is a potential candidate that combines the light-emitting principles of mechanoluminescence with the light-absorbing properties of perovskite materials. Continuous in-situ SHM with embedded sensors necessitates long-term stability. A highly stable cesium lead bromide photodetector with a carbon-based electrode and a zinc sulfide (ZnS): copper (Cu) ML layer was described in this article. The addition of a magnesium iodide (MgI₂) interfacial modifier layer between the electron transport layer (ETL) and the Perovskite interface improved the sensor's performance. Devices with the modified structure outperformed devices without the addition of MgI₂ in terms of response time and impact-sensing applications.

High-Gain MoS2/Ta2NiSe5 Heterojunction Photodetectors with Charge Transfer and Suppressing Dark Current

Emerging two-dimensional narrow band gap materials with tunable band gaps and unique electrical and optical properties have shown tremendous potential in broadband photodetection. Nevertheless, large dark currents severely hinder the performance of photodetectors. Here, a MoS₂/Ta₂NiSe₅ van der Waals heterostructure device was successfully fabricated with a high rectification ratio of ∼10⁴ and an ultralow reverse bias current of the pA level. Excitingly, the charge transfer and the generation of the built-in electric field of heterostructures have been proved by theory and experiment, which effectively suppress dark currents. The dark current of the heterostructure reduces by nearly 10⁴ compared with the pure Ta₂NiSe₅ photodetector at V_ds = 1 V. The MoS₂/Ta₂NiSe₅ device exhibits excellent photoelectric performance with the maximum responsivity of 515.6 A W^-1 and 0.7 A W^-1 at the wavelengths of 532 and 1064 nm under forward bias, respectively. In addition, the specific detectivity is up to 3.1 × 10¹³ Jones (532 nm) and 2.4 × 10⁹ Jones (1064 nm). Significantly, the device presents an ultra-high gain of 6 × 10⁷ and an exceptional external quantum efficiency of 1.2 × 10⁵% under 532 nm laser irradiation. The results reveal that the MoS₂/Ta₂NiSe₅ heterostructure provides an essential platform for the development and application of high-performance broadband optoelectronic devices.

One-step synthesis of epitaxial 3D/2D metal halide perovskite heterostructures

Facile and scalable synthesis of perovskite heterostructures with well-controlled heterointerfaces remains challenging. Herein, we developed a simple one-step solution method to prepare 3D/2D CsPbBr₃/PEA₂PbBr₄ perovskite heterostructures with a well-defined epitaxial structure in the gram scale. The formation mechanism was detailed by using in situ time-resolved photoluminescence (PL) spectroscopy analysis. In addition, a series of 3D/2D epitaxial heterostructures were also prepared by changing the organic cations or halogen anions. Due to the effective charge separation and transfer, photodetectors based on the type-II 3D/2D CsPbBr₃/PEA₂PbBr₄ heterostructures showed up to 120 times higher photoresponsivities and 50 times higher on/off ratios compared to devices based on single component perovskites.

Highly Electrochemiluminescent Cs4PbBr6@CsPbBr3 Perovskite Nanoacanthospheres and Their Application for Sensing Bisphenol A

Perovskite quantum dots (PQDs) as recently emerging electrochemiluminescence (ECL) luminophores have been paid much attention due to their good ECL activity, narrow ECL spectra, and easy preparation. However, the PQDs used for ECL sensing were mainly inherited from those PQDs prepared as strong fluorescence (FL) luminophores, which would limit the finding of highly ECL PQDs for sensing due to the very different mechanisms in generating excited-state luminophores between ECL and FL. In order to obtain highly electrochemiluminescent PQDs, for the first time we proposed to synthesize PQDs for ECL sensing rather than for FL-based analysis by optimizing the synthesis conditions. It was revealed that the volume of the precursor solution, the concentrations of CsBr and PbBr₂, the amount of capping reagents, and the synthesis reaction temperature all significantly affect the ECL activity of PQDs. On the basis of the optimization of the synthesis conditions, we obtained a new type of PQDs with high ECL activity. The new PQDs were characterized by several technologies, such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray spectrum, to be the hybrids of 3D PQDs (CsPbBr₃) and 0D PQDs (Cs₄PbBr₆) with unique morphologies, i.e., Cs₄PbBr₆@CsPbBr₃ PQD nanoacanthospheres (PNAs), in which Cs₄PbBr₆ was as the core and CsPbBr₃ served as the shell. The obtained Cs₄PbBr₆@CsPbBr₃ PNAs had much higher (>4 times) ECL activity than the prevailing 3D (CsPbBr₃) PQDs. Finally, the novel Cs₄PbBr₆@CsPbBr₃ PNAs have been applied for the ECL sensing of bisphenol A (BPA), showing a promising application of the highly electrochemiluminescent PQDs in analytical chemistry.

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.