Inorganic and Layered Perovskites for Optoelectronic Devices

Zipper-Like Dynamic Switching of Coordination Bonds Gives a Polar Bimetallic Halide Toward Self-Driven X-Ray Detection

Polar molecular crystals hold a promise for controlling bulk physical properties originated in their unique switchable polarity via structural transformation. However, the mechanisms for switching polarization are mainly limited to displacive and disorder-order phase transitions, which rarely involve the reconstruction of chemical bonds. Here, we have switched and tuned electric polarization in a bimetallic halide, (Neopentylammonium)4AgBiBr8 (1), as verified by light-excited pyroelectric effect. Most notably, its Ag-Br coordination bonds show a zipper-like dynamic switching behavior from the 'locked' to 'unlocked' state, namely, reconstruction of chemical bonds. Coupling with the dynamic ordering of organic cations, this bond-switching transition makes a contribution to switchable polarization of 1. As expected, its polarity creates pyroelectric effect for self-driven X-ray detection with high sensitivity (3.8×103 μC Gy-1 cm-2) and low limit of detection (4.8 nGy s-1). This work on the bond-switching mechanism provides an avenue to design polar molecular candidate for smart optoelectronic devices.

Insights into the pressure-dependent physical properties of cubic Ca3MF3 (M = As and Sb): First-principles calculations

Here, first-principles calculations have been employed to make a comparative study on structural, mechanical, electronic, and optical properties of new Ca3MF3 (M = As and Sb) photovoltaic compounds under pressure. The findings disclose that these two systems possess a direct band gap, showcasing a large tunable range under pressure, effectively encompassing the visible light spectrum. Adjusting various levels of hydrostatic pressure has effectively tuned both the band alignment and the effective masses of electrons and holes. Both compounds were initially identified as brittle materials at 0 GPa pressure; however, as the pressure increases, they transform, becoming highly anisotropic and ductile. Due to the material's mechanical robustness and enhanced ductility, as evidenced by its stress-induced mechanical properties, the Ca3MF3 (M = As and Sb) material shows potential for use in solar energy applications. Furthermore, as the influence of external pressure increases, the absorption edge seems to move slightly towards lower energy region. Optical properties show that the materials studied might be used from several optoelectronic devices in the visible and ultraviolet range area. Our findings show that pressure considerably influences the physicochemical properties of Ca3MF3 (M = As and Sb) compounds, which is a promising feature that can be useful for optoelectronic and photonic applications, for instance, light-emitting diodes, photodetectors, and solar cells.

Achieving High Operating-Temperature Self-powered X-Ray Detection in Multilayered Hybrid Perovskites through Arylamine Intercalation

Polar metal halide hybrid perovskites (PHPs) that exhibit outstanding bulk photovoltaic effect (BPVE), excellent semiconductor features, and strong radiation absorption ability, have shown prominent advantages in highly sensitive direct X-ray detection. However, it is still a challenge to explore PHPs with high BPVE temperature ranges, answering the demand of developing thermally stable passive X-ray detection. Herein, by intercalating arylamine into lead tribromide and inducing order-disorder phase transition, a 2D multilayered PHPs (BZA)2(MA)Pb2Br7 (BZPB, BZA = benzylamine, MA = methylamine) is synthesized. BZPB crystallizes in a polar space group Aea2 at a low-temperature phase and demonstrates a significant open-circuit of 0.3 V deriving from BPVE under X-ray irradiation. Meanwhile, the strong X-ray absorption coefficient and outstanding carrier transport capability of the bilayered lead halide framework associated with the polar BPVE give BZPB excellent X-ray detection abilities. At 0 V bias, the impressive sensitivity of BZPB is 98 µC Gy-1 cm-2. Importantly, the introduction of the rigid BZA ring increases the energy barrier of phase transition and thus dramatically enhances the X-ray detection operating temperature of BZPB up to 409 K without significant performance degradation. This work strongly reveals the great potential of rational design of metal halide hybrid perovskites for X-ray detection applications.

Enhanced performance of amplified spontaneous emission in Dion-Jacobson phase quasi-2D perovskite by facilitating carrier co-radiation

Dion-Jacobson (DJ) structured quasi-2D perovskites are promising candidates for new generation gain medium due to their excellent photoelectric performance, super environmental, and structure stability. The isolated carrier recombination with inhomogeneous mixed phase is detrimental in enhancing amplified spontaneous emission (ASE) of optically pumped DJ phase quasi-2D perovskites lasers. Here, in 1.3-propanediamine (PDA)-based DJ perovskites, the carrier dynamic behavior from the pristine sample to the Cremophor EL (Cre EL) treated sample is unraveled. Remarkably, the Cre EL treated sample displays a well-proportioned large n domain distribution, resulting in an increased radiation-state density and hence enhancing collaboration emitting between carriers. The improved collaboration emitting promotes carriers' fast relay radiation, resulting in a higher ASE performance with a threshold reduced from 11.7 to 4.8μJ/cm2, optical gain coefficient increased from 775 to 1559 cm-1 and degree-of-polarization (DOP) improved from 0.59 to 0.98. Our findings suggest that the development of DJ structured quasi-2D perovskite laser gain medium should target facilitating fast carrier co-radiation recombination.

Structural, elastic, electronic, and optical properties of lead-free halide double perovskites Cs2BꞌBꞌꞌBr6 (BꞌBꞌꞌ: BeMg, CdBe, CdGe, GeMg, GeZn, MgZn): Ab initio calculations

CONTEXT

In our study, we theoretically investigated the structural, elastic, electronic, and optical characteristics of halide double perovskites (DPs) Cs2B'B''Br6 (B'B'': BeMg, CdBe, CdGe, GeMg, GeZn, MgZn). Structural stabilities were assessed based on the enthalpy of formation, tolerance factor, and elastic constants. Ductile and brittle behavior was examined using Poisson and Pugh's ratios. Based on electronic calculations, it has been concluded that Cs2B'B''Br6 double perovskites with B'B'' as BeMg or CdBe exhibit direct bandgaps, whereas those with B'B'' as CdGe, GeMg, GeZn, or MgZn display indirect bandgaps. Additionally, we thoroughly investigated the optical properties of double perovskites by analyzing all their parameters in the energy range spanning 0 to 13 eV. Primary absorption was noted in the ultraviolet (UV) region.

METHODS

In this work, all calculations were performed using the Wien2k package. The generalized gradient approximation (GGA) and the modified Becke-Johnson (mBJ) method were employed to describe the exchange-correlation interactions.

Chemical Mapping of Excitons in Halide Double Perovskites

Halide double perovskites comprise an emerging class of semiconductors with tremendous chemical and electronic diversity. While their band structure features can be understood from frontier-orbital models, chemical intuition for optical excitations remains incomplete. Here, we use ab initio many-body perturbation theory within the GW and the Bethe-Salpeter equation approach to calculate excited-state properties of a representative range of Cs2BB'Cl6 double perovskites. Our calculations reveal that double perovskites with different combinations of B and B' cations display a broad variety of electronic band structures and dielectric properties and form excitons with binding energies ranging over several orders of magnitude. We correlate these properties with the orbital-induced anisotropy of charge-carrier effective masses and the long-range behavior of the dielectric function by comparing them with the canonical conditions of the Wannier-Mott model. Furthermore, we derive chemically intuitive rules for predicting the nature of excitons in halide double perovskites using computationally inexpensive density functional theory calculations.

Controllably modulated asymmetrical photoresponse with a nonvolatile memory effect in a single CH3NH3PbI3 micro/nanowire for photorectifiers and photomemory

Nanostructured hybrid organic-inorganic perovskites exhibit remarkable photodetection performance due to their abundant surface states and high responsivity to visible light. However, in traditional photodetectors with a symmetrical configuration of two-terminal electrodes, the photoresponse is independent of bias polarity. Moreover, for self-powered photodetectors, an asymmetric structure of the chemical composition, such as p-n and Schottky junctions, and two different electrodes are necessary. Herein, we demonstrate a modulable asymmetrical photoresponse by packing only one electrode end in a single CH3NH3PbI3 micro/nanowire with two symmetrical Ag electrodes. This not only enables the high performance of light- and bias-modulated multifunctional photorectifiers and self-powered photodetectors, but also allows controllable implementation of nonvolatile photomemory with a tunable spectral responsivity and range. At an unpacked electrode interface, trace moisture in the environment promotes a good bonding of Ag+ and I-, substantially decreasing the interface barrier. Conversely, at a packed electrode interface, abundant surface states can be well preserved, leading to a high interface barrier. Notably, under a large voltage and strong light, the redox of Ag/AgI at the unpacked electrode interface and the injection and ejection of holes at the packed electrode interface can be reversibly conducted by inverting the voltage polarity, enabling a controllable nonvolatile modulation. Therefore, by clarifying the actual origin of the photoelectrical response of CH3NH3PbI3 micro/nanowires at electrode interfaces, high-performance multifunctional photorectifiers and self-powered photodetectors based on asymmetrical interface photovoltaic effects with two symmetrical electrodes can be controllably realized. Furthermore, by precise cooperative modulation of two electrode interface states with a large voltage and strong illumination, nonvolatile photomemory with a tunable spectral responsivity and range can be implemented.

Synergistic Effect of Cation Composition Engineering of Hybrid Cs1-x FAx PbBr3 Nanocrystals for Self-Healing Electronics Application

Mixed-cation hybrid perovskite nanocrystal (HPNC) with high crystallinity, color purity, and tunable optical bandgap offers a practical pathway toward next-generation displays. Herein, a two-step modified hot-injection combined with cation compositional engineering and surface treatment to synthesize high-purity cesium/formamidinium lead bromide HPNCs(Cs_1-x FA_x PbBr₃ ) is presented. The optimized Cs_0.5 FA_0.5 PbBr₃ light-emitting devices (LEDs) exhibit uniform luminescence of 3500 cd m^-2 and a prominent current efficiency of 21.5 cd A^-1 . As a proof of concept, a self-healing polymer (SHP) integrated with white LED backlight and laser prototypes exhibited 4 h autonomous self-healing through the synergistic effect of weak reversible imine bonds and stronger H-bonds. First, the SHP-HPNCs-initial and SHP-HPNCs-cut possess high long-term stability and dramatically suppressed lead leakage as low as 0.6 ppm along with a low leakage rate of 1.11 × 10^-5 cm² and 3.36 × 10^-5 cm² even over 6 months in water. Second, the Cs_0.5 FA_0.5 PbBr₃ HPNCs and SHP-induced shattered-repaired perovskite glass substrate show the lowest lasing threshold values of 1.24 and 8.58 µJ cm^-2 , respectively. This work provides an integrative and in-depth approach to exploiting SHP with intrinsic and entropic self-healing capabilities combined with HPNCs to develop robust and reliable soft-electronic backlight and laser applications.

Improved Performance of All-Inorganic Perovskite Light-emitting Diodes via Nanostructured Stamp Imprinting

Halide perovskites are emerging emitters with excellent optoelectronic properties. Contrary to the large grain fabrication goal in perovskite solar cells, perovskite light-emitting diodes (PeLEDs) based on small grain enable efficient radiative recombination because of relatively higher charge carrier densities due to spatial confinement. However, achieving small-sized grain growth with superior crystal quality and film morphology remains a challenge. In this work, we demonstrated a nanostructured stamp thermal imprinting strategy to boost the surface coverage and improve the crystalline quality of CsPbBr₃ film, particularly confine the grain size, leading to the improvement of luminance and efficiency of PeLEDs. We improved the thermal imprinting process utilizing the nanostructured stamp to selectively manipulate the nucleation and growth in the nanoscale region and acquire small-sized grain accompanied by improved crystal quality and surface morphology of the film. By optimizing the imprinting pressure and the period of the nanostructures, appropriate grain size, high surface coverage, small surface roughness and improved crystallization could be achieved synchronously. Finally, the maximum luminance and efficiency of PeLEDs achieved by nanostructured stamp imprinting with a period of 320 nm are 67600 cd/m² and 16.36 cd/A, respectively. This corresponds to improvements of 123 % in luminance and 100 % in efficiency, compared to that of PeLEDs without the imprinting.

Review on Perovskite Semiconductor Field-Effect Transistors and Their Applications

Perovskite materials are considered as the most alluring successor to the conventional semiconductor materials to fabricate solar cells, light emitting diodes and electronic displays. However, the use of the perovskite semiconductors as a channel material in field effect transistors (FET) are much lower than expected due to the poor performance of the devices. Despite low attention, the perovskite FETs are used in widespread applications on account of their unique opto-electrical properties. This review focuses on the previous works on perovskite FETs which are summarized into tables based on their structures and electrical properties. Further, this review focuses on the applications of perovskite FETs in photodetectors, phototransistors, light emitting FETs and memory devices. Moreover, this review highlights the challenges faced by the perovskite FETs to meet the current standards along with the future directions of these FETs. Overall, the review summarizes all the available information on existing perovskite FET works and their applications reported so far.

Efficient all-inorganic red perovskite light-emitting diodes with dual-interface-modified perovskites by vapor deposition

Interface engineering has been extensively used in perovskite light-emitting diodes (PeLEDs), which proves to be an effective and intelligent approach for surface defect passivation. However, the existing passivation strategy is restricted to the solution process, which results in poor compatibility with vapor-deposited PeLEDs and moderate controllability. Here, we propose a dual-interface modification strategy to facilitate the performance improvement of vapor-deposited all-inorganic red PeLEDs. An ultrathin phenylethanamine bromide (PEABr) layer is introduced to both the upper and lower interfaces of the vapor-deposited perovskite emission layer by vapor deposition. The vapor deposition of the PEABr with fine-controlled film thickness is a reliable and simple process and compatible with vapor-deposited all-inorganic PeLEDs. The dual-interface modification plays an observable role in manipulating the crystallization and surface morphology of the CsPbBrI₂ film, which is of significance for the improvement of the PeLEDs' performance. As a result, the red PeLEDs achieve a maximum luminance and external quantum efficiency of 2338 cd/m² and 1.75%, corresponding to enhancements of 2.75 and 5.25 times compared with those of PeLEDs without PEABr. This approach paves the way to high-efficiency all-evaporated all-inorganic PeLEDs.

Photoluminescence enhancement study in a Bi-doped Cs2AgInCl6 double perovskite by pressure and temperature-dependent self-trapped exciton emission

Here, we report a halide precursor acid precipitation method to synthesize Cs₂AgIn_1-xBi_xCl₆ (x = 0, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, and 1) microcrystals. Cs₂AgInCl₆ and Bi derivative double perovskites show broadband white light emission via self-trapped excitons (STEs) and have achieved the highest internal quantum efficiency of up to 52.4% at x = 0.08. Synchrotron X-ray diffraction confirmed the linear increase of lattice parameters and cell volume with Bi³⁺ substitution at In³⁺ sites. Absorbance, photocurrent excitation, and photoluminescence excitation spectra are used to observe possible transitions from the valence to the conduction band or free exciton (FE) states as well as transitions within local Bi³⁺ states. The broadband photoluminescence is quenched via a single nonradiative process with an activation energy ΔE = 1490 cm^-1 for Cs₂AgIn_0.92Bi_0.08Cl₆. Under normal conditions, we observed STE emission, but applying external pressure alters the electronic structure such that at elevated pressure, the only emission via the FE state is observed. We anticipate that structure, temperature and pressure-dependent photoluminescence studies will help the future use of a single-source lead-free double perovskite for white light-emitting diode applications.

Tuning Dielectric Transitions in Two-Dimensional Organic-Inorganic Hybrid Lead Halide Perovskites

Organic-inorganic hybrid metal halide perovskites possessing unique two-dimensional (2D)-layered structures have been demonstrated with excellent molecular tunability and stability, especially the promising semiconductor properties for solar cell applications. In this work, three 2D lead halide organic-inorganic hybrid perovskites (IAA)₂PbX₄ (IAA = isoamylammonium cation and X = Cl, Br, and I) were synthesized by employing a solution processing method and demonstrate distinct tuning solid-state phase transitions coupled with dielectric responses, as well as light absorption properties. Among the title perovskites, the phase transition temperature decreases gradually, and their band gap also indicates a narrowing trend. The results are mainly derived from slight changes in the crystal structure by halogen regulation. These findings might provide an effective crystal engineering strategy for exploring high-performance functional perovskite materials.

Molecular and Supramolecular Structures of Triiodides and Polyiodobismuthates of Phenylenediammonium and Its N,N-dimethyl Derivative

Despite remarkable progress in photoconversion efficiency, the toxicity of lead-based hybrid perovskites remains an important issue hindering their applications in consumer optoelectronic devices, such as solar cells, LED displays, and photodetectors. For that reason, lead-free metal halide complexes have attracted great attention as alternative optoelectronic materials. In this work, we demonstrate that reactions of two aromatic diamines with iodine in hydroiodic acid produced phenylenediammonium (PDA) and N,N-dimethyl-phenylenediammonium (DMPDA) triiodides, PDA(I₃)₂⋅2H₂O and DMPDA(I₃)I, respectively. If the source of bismuth was added, they were converted into previously reported PDA(BiI₄)₂⋅I₂ and new (DMPDA)₂(BiI₆)(I₃)⋅2H₂O, having band gaps of 1.45 and 1.7 eV, respectively, which are in the optimal range for efficient solar light absorbers. All four compounds presented organic–inorganic hybrids, whose supramolecular structures were based on a variety of intermolecular forces, including (N)H⋅⋅⋅I and (N)H⋅⋅⋅O hydrogen bonds as well as I⋅⋅⋅I secondary and weak interactions. Details of their molecular and supramolecular structures are discussed based on single-crystal X-ray diffraction data, thermal analysis, and Raman and optical spectroscopy.

Fiber‐Shaped Electronic Devices

Textile electronics embedded in clothing represent an exciting new frontier for modern healthcare and communication systems. Fundamental to the development of these textile electronics is the development of the fibers forming the cloths into electronic devices. An electronic fiber must undergo diverse scrutiny for its selection for a multifunctional textile, viz., from the material selection to the device architecture, from the wearability to mechanical stresses, and from the environmental compatibility to the end‐use management. Herein, the performance requirements of fiber‐shaped electronics are reviewed considering the characteristics of single electronic fibers and their assemblies in smart clothing. Broadly, this article includes i) processing strategies of electronic fibers with required properties from precursor to material, ii) the state‐of‐art of current fiber‐shaped electronics emphasizing light‐emitting devices, solar cells, sensors, nanogenerators, supercapacitors storage, and chromatic devices, iii) mechanisms involved in the operation of the above devices, iv) limitations of the current materials and device manufacturing techniques to achieve the target performance, and v) the knowledge gap that must be minimized prior to their deployment. Lessons learned from this review with regard to the challenges and prospects for developing fiber‐shaped electronic components are presented as directions for future research on wearable electronics.

State of the Art and Prospects for Halide Perovskite Nanocrystals

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

Flexible Light-to-Frequency Conversion Circuits Built with Si-Based Frequency-to-Digital Converters via Complementary Photosensitive Ring Oscillators with p-Type SWNT and n-Type a-IGZO Thin Film Transistors

In this study, as system-level photodetectors, light-to-frequency conversion circuits (LFCs) are realized by i) photosensitive ring oscillators (ROs) composed of amorphous indium-gallium-zinc-oxide/single-walled carbon nanotube (a-IGZO/SWNT) thin film transistors (TFTs) and ii) phase-locked-loop Si circuits built with frequency-to-digital converters (PFDC). The 3-stage ROs and logic gates based on a-IGZO/SWNT TFTs successfully demonstrate its performance on flexible substrates. Herein, along with the advantage of scalability, a-IGZO films are used as photosensitive n-type TFTs and SWNTs are employed as photo-insensitive p-type TFTs for better photosensitivity in circuit level. Through the controlling a post-annealing condition of a-IGZO film, responsivities and detectivities of a-IGZO TFTs are obtained as 36 AW^-1 and 0.3 × 10¹² Jones for red, 93 AW^-1 and 3.1 × 10¹² Jones for green, and 194 AW^-1 and 11.7 × 10¹² Jones for blue. Furthermore, as an advanced demonstration for practical application of LFCs, a unique circuit (i.e., PFDC) is designed to analyze the generated oscillation frequency (f_osc ) from the LFC device and convert it to a digital code. As a result, the designed PFDC can exactly count the generated f_osc from the flexible a-IGZO/SWNT ROs under light illumination with an outstanding sensitivity and assign input frequencies to respective digital code.

Light-induced pyroelectric property of self-powered photodetectors based on all-inorganic perovskite quantum dots

All-inorganic cesium lead bromine (CsPbBr₃) perovskites quantum dots (QDs) are one of the most photoelectric materials due to their high absorption coefficient, pronounced quantum-size effect, tunable optical property. Here, a self-powered PD based on all-inorganic CsPbBr₃perovskites QDs is fabricated and demonstrated. The light-induced pyroelectric effect is utilized to modulate the optoelectronic processes without the external power supply. The working mechanism of the PD is carefully investigated upon 532 nm laser illumination and the minimum recognizable response time of the self-powered PD is 1.5μs, which are faster than those of most previously reported wurtzite nanostructure PDs. Meanwhile, the frequency and temperature independence of the self-powered PD are experimented and summarized. The self-powered PD with high performance is expected to have extensive applications in solar cell, energy harvesting, resistive random access memory.

Mechanical switching of orientation-related photoluminescence in deep-blue 2D layered perovskite ensembles

The synergy between the organic component of two-dimensional (2D) metal halide layered perovskites and flexible polymers offers an unexplored window to tune their optical properties at low mechanical stress. Thus, there is a significant interest in exploiting their PL anisotropy by controlling their orientation and elucidating their interactions. Here, we apply this principle to platelet structures of micrometre lateral size that are synthesized in situ into free-standing polymer films. We study the photoluminescence of the resulting films under cyclic mechanical stress and observe an enhancement in the emission intensity up to ∼2.5 times along with a switch in the emission profile when stretching the films from 0% to 70% elongation. All the films recovered their initial emission intensity when releasing the stress throughout ca. 15 mechanical cycles. We hypothesize a combined contribution from reduced reabsorption, changes on in-plane and out-of-plane dipole moments that stem from different orientation of the platelets inside the film, and relative sliding of platelets within oriented stacks while stretching the films. Our results reveal how low-mechanical stress affects 2D layered perovskite aggregation and orientation, an open pathway toward the design of strain-controlled emission.

Lead-Free Halide Perovskites for Light Emission: Recent Advances and Perspectives

Lead-based halide perovskites have received great attention in light-emitting applications due to their excellent properties, including high photoluminescence quantum yield (PLQY), tunable emission wavelength, and facile solution preparation. In spite of excellent characteristics, the presence of toxic element lead directly obstructs their further commercial development. Hence, exploiting lead-free halide perovskite materials with superior properties is urgent and necessary. In this review, the deep-seated reasons that benefit light emission for halide perovskites, which help to develop lead-free halide perovskites with excellent performance, are first emphasized. Recent advances in lead-free halide perovskite materials (single crystals, thin films, and nanocrystals with different dimensionalities) from synthesis, crystal structures, optical and optoelectronic properties to applications are then systematically summarized. In particular, phosphor-converted LEDs and electroluminescent LEDs using lead-free halide perovskites are fully examined. Ultimately, based on current development of lead-free halide perovskites, the future directions of lead-free halide perovskites in terms of materials and light-emitting devices are discussed.

Air-Stable Bulk Halide Single-Crystal Scintillator Cs3Cu2I5 by Melt Growth: Intrinsic and Tl Doped with High Light Yield

Ternary metal halides with large exciton binding energy have recently gained considerable attention in the optoelectronic field due to their high photoluminescence quantum yield and large Stokes shift. Here, efficient scintillators are designed based on these advantageous properties. For the first time, bulk Cs₃Cu₂I₅ is grown using a melt method other than the intensively reported solution growth, and behaved as an intrinsic scintillator, emitting bright blue (∼450 nm) light under X-ray and γ-ray irradiation. Successful Tl doping at Cs sites tune the emission band over the entire visible range (400-700 nm) due to the synergetic effects of self-trapped excitons (STEs) and Tl centers. Notably, after doping with 1% Tl⁺, the scintillation light yield of Cs₃Cu₂I₅ increases by nearly three times to 51 000 ± 2000 ph/MeV (Cs-137, 662 keV). Cs₃Cu₂I₅:Tl shows a higher energy resolution of 4.5% at 662 keV than that of NaI:Tl and an excellent nonproportionality (<3%) in the γ-ray energy range of 60-1275 keV. A model of energy relaxation in Cs₃Cu₂I₅:Tl scintillators is proposed and discussed. In particular, it is the first Cu-based halide scintillator that has air stability, good stopping power, and the ability to grow large bulk single crystals for practical application. This work provides a strategy for tuning and broadening the spectral range of STE emitters, and bridges the lead-free halide derivatives with scintillators.

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

In recent years, impurity-doped nanocrystal light-emitting diodes (LEDs) have aroused both academic and industrial interest since they are highly promising to satisfy the increasing demand of display, lighting, and signaling technologies. Compared with undoped counterparts, impurity-doped nanocrystal LEDs have been demonstrated to possess many extraordinary characteristics including enhanced efficiency, increased luminance, reduced voltage, and prolonged stability. In this review, recent state-of-the-art concepts to achieve high-performance impurity-doped nanocrystal LEDs are summarized. Firstly, the fundamental concepts of impurity-doped nanocrystal LEDs are presented. Then, the strategies to enhance the performance of impurity-doped nanocrystal LEDs via both material design and device engineering are introduced. In particular, the emergence of three types of impurity-doped nanocrystal LEDs is comprehensively highlighted, namely impurity-doped colloidal quantum dot LEDs, impurity-doped perovskite LEDs, and impurity-doped colloidal quantum well LEDs. At last, the challenges and the opportunities to further improve the performance of impurity-doped nanocrystal LEDs are described.

Transparent, flexible MAPbI3 perovskite microwire arrays passivated with ultra-hydrophobic supramolecular self-assembly for stable and high-performance photodetectors

The emergence of organic-inorganic hybrid perovskites (OHPs) has revolutionised the potential performance of optoelectronic devices; most perovskites are opaque and hence incompatible with transparent optoelectronics and sensitive to environmental degradation. Here, we have reported a single-step fabrication of ultra-long MAPbI₃ perovskite microwire arrays over a large area using stencil lithography based on sequential vacuum sublimation. The environmental stability of MAPbI₃ is empowered with a newly designed and synthesized transparent supramolecular self-assembly based on a mixture of two tripodal l-Phe-C₁₁H₂₃/C₇F₁₅ molecules, which showed a contact angle of 105° and served as ultra-hydrophobic passivation layers for more than 45 days in an ambient atmosphere. The MAPbI₃ microwire arrays passivated with the supramolecular self-assembly demonstrated for the first time both excellent transparency of ∼89% at 550 nm and a remarkable photoresponse with a photo-switching ratio of ∼10⁴, responsivity of 789 A W^-1, detectivity of 10¹⁴ Jones, linear dynamic range of ∼122 dB, and rise time of 432 μs. Furthermore, the photodetector fabricated on a flexible PET substrate demonstrated robust mechanical flexibility even beyond 1200 bending cycles. Therefore, the scalable stencil lithography and supramolecular passivation approaches have the potential to deliver next-generation transparent, flexible, and stable optoelectronic devices.

Materials chemistry and engineering in metal halide perovskite lasers

The invention and development of the laser have revolutionized science, technology, and industry. Metal halide perovskites are an emerging class of semiconductors holding promising potential in further advancing the laser technology. In this Review, we provide a comprehensive overview of metal halide perovskite lasers from the viewpoint of materials chemistry and engineering. After an introduction to the materials chemistry and physics of metal halide perovskites, we present diverse optical cavities for perovskite lasers. We then comprehensively discuss various perovskite lasers with particular functionalities, including tunable lasers, multicolor lasers, continuous-wave lasers, single-mode lasers, subwavelength lasers, random lasers, polariton lasers, and laser arrays. Following this a description of the strategies for improving the stability and reducing the toxicity of metal halide perovskite lasers is provided. Finally, future research directions and challenges toward practical technology applications of perovskite lasers are provided to give an outlook on this emerging field.

Device Engineering for All-Inorganic Perovskite Light-Emitting Diodes

Recently, all-inorganic perovskite light-emitting diodes (PeLEDs) have attracted both academic and industrial interest thanks to their outstanding properties, such as high efficiency, bright luminance, excellent color purity, low cost and potentially good operational stability. Apart from the design and treatment of all-inorganic emitters, the device engineering is another significant factor to guarantee the high performance. In this review, we have summarized the state-of-the-art concepts for device engineering in all-inorganic PeLEDs, where the charge injection, transport, balance and leakage play a critical role in the performance. First, we have described the fundamental concepts of all-inorganic PeLEDs. Then, we have introduced the enhancement of device engineering in all-inorganic PeLEDs. Particularly, we have comprehensively highlighted the emergence of all-inorganic PeLEDs, strategies to improve the hole injection, approaches to enhance the electron injection, schemes to increase the charge balance and methods to decrease the charge leakage. Finally, we have clarified the issues and ways to further enhance the performance of all-inorganic PeLEDs.