Lead-Free Antimony-Based Light-Emitting Diodes through the Vapor-Anion-Exchange Method

Two-dimensional Cs3Sb2Br9 inducing transformation of three-dimensional CsPbBr3 to nanoplates

This communication describes an effective morphological control strategy involving introducing two-dimensional (2D) Cs3Sb2Br9 to induce a transformation of three-dimensional (3D) CsPbBr3 to 2D nanoplates (NPLs). By tuning the Sb/Pb ratio, 2D CsPbBr3 NPLs exhibiting a deep-blue emission centered at a wavelength of 464 nm with an FWHM of 24 nm have been produced. The absence of organic ligands in these high-quality 2D NPLs mitigate the instability issue induced by organic ligand migration and penetration, and these NPLs exhibit 80% of the initial PL intensity after 55 days.

Luminescent Behavior of Sb3+-Activated Luminescent Metal Halide

Metal halide perovskites have unparalleled optoelectronic properties and broad application potential and are expected to become the next epoch-making optoelectronic semiconductors. Although remarkable achievements have been achieved with lead halide perovskites, the toxicity of lead inhibits the development of such materials. Recently, Sb3+-activated luminescent metal halide perovskite materials with low toxicity, high efficiency, broadband, large Stokes shift, and emission wavelengths covering the entire visible and near-infrared regions have been considered one of the most likely luminescent materials to replace lead halide perovskites. This review reviews the synthesis, luminescence mechanism, structure, and luminescence properties of the compounds. The basic luminescence properties of Sb3+-activated luminescent metal halide perovskites and their applications in WLED, electroluminescence LED, temperature sensing, optical anti-counterfeiting, and X-ray scintillators are introduced. Finally, the development prospects and challenges of Sb3+-activated luminescent metal halide perovskites are discussed.

Recent Advances and Future Perspectives of Lead-Free Halide Perovskites for Photocatalytic CO2 Reduction

It is still challenging to design and develop the state-of-the-art photocatalysts toward CO2 photoreduction. Enormous researchers have focused on the halide perovskites in the photocatalytic field for CO2 photoreduction, due to their excellent optical and physical properties. The toxicity of lead-based halide perovskites prevents their large-scale applications in photocatalytic fields. In consequence, lead-free halide perovskites (LFHPs) without the toxicity become the promising alternatives in the photocatalytic application for CO2 photoreduction. In recent years, the rapid advances of LFHPs have offer new chances for the photocatalytic CO2 reduction of LFHPs. In this review, we summarize not only the structures and properties of A2 BX6 , A2 B(I)B(III)X6 , and A3 B2 X9 -type LFHPs but also their recent progresses on the photocatalytic CO2 reduction. Furthermore, we also point out the opportunities and perspectives to research LFHPs photocatalysts for CO2 photoreduction in the future.

Stabilizing FASnI3-based perovskite light-emitting diodes with crystallization control

The toxicity of lead presents a critical challenge for the application of perovskite optoelectronics. Lead-free perovskite solar cells were achieved with formamidinium tin iodide (FASnI₃) perovskites, exhibiting decent power-conversion efficiencies (PCEs) of up to 14%, with >98% of the initial PCE retained after 3000 h of storage. However, when employed in light-emitting applications, FASnI₃-based perovskite LEDs (PeLEDs) show limited stability, with T₅₀ lifetimes of up to 0.25 h at 10 mA cm^-2. Here, we improve the stability of FASnI₃-based PeLEDs through the inclusion of a two-dimensional precursor phenethylamine iodide (PEAI), allowing controlled crystallization of the mixed-dimensional perovskite emitters. The density of defects is found to be reduced, accompanied by the suppression of oxidation from Sn²⁺ to Sn⁴⁺. Using an optimized perovskite composition, we achieve an EQE of 1.5% (a ∼10-fold improvement over the control devices), a maximum radiance of 145 W sr^-1 m^-2, and a record-long T₅₀ lifetime of 10.3 h at 100 mA cm^-2 for FASnI₃-based PeLEDs. Our results illuminate an alternative path toward lead-free PeLED applications.

Advances in electrically driven light-emitting diodes based on lead-free metal halides

The emerging lead halide perovskites show great potential for their use as emitters in electrically driven light-emitting diodes (LEDs) with external quantum efficiency (EQE) over 25%. While the toxicity of lead and inferior device stability are the main obstacles for their commercialization, replacing Pb²⁺ with low- or non-toxic metal ions to form low- or zero-dimensional structures provides an alternative approach to effectively tackle these issues. Recently, luminescent lead-free metal halides have been increasingly developed toward eco-friendly and highly efficient electroluminescence. In this feature article, we give a brief overview of recent advances in luminescent lead-free metal halides and their applications in electrically driven LEDs. The challenges and prospects in this field are outlined at the end.

Unraveling the Defect-Dominated Broadband Emission Mechanisms in (001)-Preferred Two-Dimensional Layered Antimony-Halide Perovskite Film

By adding molar-controlled SbCl₃ in a Cs₃Sb₂Cl₉ precursor, we employed a low-temperature solution-processed approach to prepare high-quality (001)-preferred Cs₃Sb₂Cl₉ thin film, which demonstrates a stable defect-dominated broadband emission at room temperature. Density functional theory calculations reveal that the defect emission originates from the donor-acceptor pair (DAP) recombination between chlorine vacancy (V_Cl) and cesium vacancy (V_Cs). Furthermore, V_Cl + V_Cs DAP is more stable on the (001) surface. The improved film quality and the more stable V_Cl + V_Cs DAP increase the activation energy related to defect states, resulting in an enhancement of the defect emission for the high-quality (001)-preferred film. This work provides deep insight into the key role of the (001) surface in defect emission and a feasible strategy to enhance the defect emission in 2D halide perovskites A₃B₂X₉ (A = CH₃NH₃, Cs, Rb; B = Bi, Sb; X = Cl, Br, I) by control of the thin film preferred orientation.

Vapor-Assisted In Situ Recrystallization for Efficient Tin-Based Perovskite Light-Emitting Diodes

Tin-based perovskites are a promising candidates to replace their toxic lead-based counterparts in optoelectronic applications, such as light-emitting diodes (LEDs). However, the development of tin perovskite LEDs is slow due to the challenge of obtaining high-quality tin perovskite films. Here, a vapor-assisted spin-coating method is developed to achieve high-quality tin perovskites and high-efficiency LEDs. It is revealed that solvent vapor can lead to in situ recrystallization of tin perovskites during the film-formation process, thus significantly improving the crystalline quality with reduced defects. An antioxidant additive is further introduced to suppress the oxidation of Sn²⁺ and increase the photoluminescence quantum efficiency up to ≈30%, which is an approximately fourfold enhancement in comparison with that of the control method. As a result, efficient tin perovskite LEDs are achieved with a peak external quantum efficiency of 5.3%, which is among the highest efficiency of lead-free perovskite LEDs.

Electronic Structures and Photoelectric Properties in Cs3Sb2X9 (X = Cl, Br, or I) under High Pressure: A First Principles Study

Lead-free perovskites of Cs₃Sb₂X₉ (X = Cl, Br, or I) have attracted wide attention owing to their low toxicity. High pressure is an effective and reversible method to tune bandgap without changing the chemical composition. Here, the structural and photoelectric properties of Cs₃Sb₂X₉ under high pressure were theoretically studied by using the density functional theory. The results showed that the ideal bandgap for Cs₃Sb₂X₉ can be achieved by applying high pressure. Moreover, it was found that the change of the bandgap is caused by the shrinkage of the Sb-X long bond in the [Sb₂X₉]^3- polyhedra. Partial density of states indicated that Sb-5s and X-p orbitals contribute to the top of the valence band, while Sb-5p and X-p orbitals dominate the bottom of the conduction band. Moreover, the band structure and density of states showed significant metallicity at 38.75, 24.05 GPa for Cs₃Sb₂Br₉ and Cs₃Sb₂I₉, respectively. Moreover, the absorption spectra showed the absorption edge redshifted, and the absorption coefficient of the Cs₃Sb₂X₉ increased under high pressure. According to our calculated results, the narrow bandgap and enhanced absorption ability under high pressure provide a new idea for the design of the photovoltaic and photoelectric devices.

Ion Migration in Perovskite Light-Emitting Diodes: Mechanism, Characterizations, and Material and Device Engineering

In recent years, perovskite light-emitting diodes (PeLEDs) have emerged as a promising new lighting technology with high external quantum efficiency, color purity, and wavelength tunability, as well as, low-temperature processability. However, the operational stability of PeLEDs is still insufficient for their commercialization. The generation and migration of ionic species in metal halide perovskites has been widely acknowledged as the primary factor causing the performance degradation of PeLEDs. Herein, this topic is systematically discussed by considering the fundamental and engineering aspects of ion-related issues in PeLEDs, including the material and processing origins of ion generation, the mechanisms driving ion migration, characterization approaches for probing ion distributions, the effects of ion migration on device performance and stability, and strategies for ion management in PeLEDs. Finally, perspectives on remaining challenges and future opportunities are highlighted.

Synthesis of Stable Lead-Free Cs3 Sb2 (Brx I1- x )9 (0 ≤ x ≤ 1) Perovskite Nanoplatelets and Their Application in CO2 Photocatalytic Reduction

Exploring photocatalysts to foster CO₂ photoreduction into high value-added chemicals is of great significance. Lead halide perovskites (LHPs) have recently been extensively investigated as photocatalysts, owing to their facile fabrication and prominent optoelectronic properties. However, the toxicity of lead and instability will hinder their future large-scale applications. To address these challenges, a series of lead-free Sb-based all-inorganic mixed halide perovskite Cs₃ Sb₂ (Br_x I_{1- x} )₉ (0 ≤ x ≤ 1) nanoplatelets (NPLs) is synthesized. The perovskite NPLs are prepared using a ligand-assisted re-precipitation approach at 50 °C. The authors observe the tunability of their optical band gaps from 2.1 to 2.5 eV, and they can maintain the excellent stability over 120 h under heating at 100 °C or UV light irradiation. The resultant materials are employed as efficient photocatalysts for visible-light driven CO₂ reduction at the gas-solid interface. The Cs₃ Sb₂ (Br_0.7 I_0.3 )₉ perovskite NPLs afford an impressive overall yield of 27.7 µmol g^-1 for the selective photocatalytic conversion of CO₂ into CO. This study represents a significant demonstration for practical artificial photosynthesis by using LHP materials as photocatalysts.

Research progress of ABX3-type lead-free perovskites for optoelectronic applications: materials and devices

We summarize the development and application of ABX3-type lead-free halide perovskite materials, especially in optoelectronic devices.

Recent Advancements in Nontoxic Halide Perovskites: Beyond Divalent Composition Space

Since the inception of organic-inorganic hybrid perovskites of ABX3 stoichiometry in 2009, there has been enormous progress in envisaging efficient solar cell materials throughout the world, from both the theoretical and experimental perspectives. Despite achieving 25.5% efficiency, hybrid halide perovskites are still facing two main challenges: toxicity due to the presence of lead and device stability. Two particular families with A3B2X9 and A2MM'X6 stoichiometries have emerged to address these two prime concerns, which have restrained the advancement of solar energy harvesting. Several investigations, both experimental and theoretical, are being conducted to explore the holy-grail materials, which could be optimum for not only efficient but also stable and nontoxic photovoltaics technology. However, the trade-off among stability, efficiency, and toxicity in such solar energy materials is yet to be completely resolved, which requires a systematic overview of A3B2X9- and A2MM'X6-based solar cell materials. Therefore, in this timely and relevant perspective, we have focused on these two particular promising families of perovskite materials. We have portrayed a roadmap projecting the recent advancements from both theoretical and experimental perspectives for these two exciting and promising solar energy material families while amalgamating our critical viewpoint with a future outlook.

Spectral Stable Blue-Light-Emitting Diodes via Asymmetric Organic Diamine Based Dion-Jacobson Perovskites

The spectral instability issue is a challenge in blue perovskite light-emitting diodes (PeLEDs). Dion–Jacobson (DJ) phase perovskites are promising alternatives to achieve high-quality blue PeLEDs. However, the current exploration of DJ phase perovskites is focused on symmetric divalent cations, and the corresponding efficiency of blue PeLEDs is still inferior to that of green and red ones. In this work, we report a new type of DJ phase CsPb(Br/Cl)₃ perovskite via introduction of an asymmetric molecular configuration as the organic spacer cation in perovskites. The primary and tertiary ammonium groups on the asymmetric cations bridge with the lead halide octahedra forming the DJ phase structures. Stable photoluminescence spectra were demonstrated in perovskite films owing to the suppressed halide segregation. Meanwhile, the radiative recombination efficiency of charges is improved significantly as a result of the confinement effects and passivation of charge traps. Finally, we achieved an external quantum efficiency of 2.65% in blue PeLEDs with stable spectra emission under applied bias voltages. To our best knowledge, this is the first report of asymmetric cations used in PeLEDs, which provides a facile solution to the halide segregation issue in PeLEDs.

Highly Efficient Light-Emitting Diodes Based on an Organic Antimony(III) Halide Hybrid

As low-dimensional lead-free hybrids with higher stability and lower toxicity than those of three-dimensional lead perovskites, organic antimony(III) halides show great application potential in opt-electronic field owing to diverse topologies along with exceptional optical properties. We report herein an antimony(III) hybrid (MePPh₃ )₂ SbCl₅ with a zero-dimensional (0D) structure, which exhibits brilliant orange emission peaked at 593 nm with near-unity photoluminescent quantum yield (99.4 %). The characterization of photophysical properties demonstrates that the broadband emission with a microsecond lifetime (3.24 μs) arises from self-trapped emission (STE). Electrically driven organic light-emitting diodes (OLEDs) based on neat and doped films of (MePPh₃ )₂ SbCl₅ were fabricated. The doped devices show significant improvement in comparison to non-doped OLEDs. Owing to the much improved surface morphology and balanced carrier transport in light-emitting layers of doped devices, the peak luminance, current efficiency (CE) and external quantum efficiency (EQE) are boosted from 82 cd m^-2 to 3500 cd m^-2 , 1.1 cd A^-1 to 6.8 cd A^-1 , and 0.7 % to 3.1 % relative to non-doped devices, respectively.

Advances and Challenges in Two-Dimensional Organic-Inorganic Hybrid Perovskites Toward High-Performance Light-Emitting Diodes

Two-dimensional (2D) perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties. Compared with 3D perovskites, 2D perovskites have natural quantum well structures, large exciton binding energy (E_b) and outstanding thermal stability, which shows great potential in the next-generation displays and solid-state lighting. In this review, the fundamental structure, photophysical and electrical properties of 2D perovskite films were illustrated systematically. Based on the advantages of 2D perovskites, such as special energy funnel process, ultra-fast energy transfer, dense film and low efficiency roll-off, the remarkable achievements of 2D perovskite light-emitting diodes (PeLEDs) are summarized, and exciting challenges of 2D perovskite are also discussed. An outlook on further improving the efficiency of pure-blue PeLEDs, enhancing the operational stability of PeLEDs and reducing the toxicity to push this field forward was also provided. This review provides an overview of the recent developments of 2D perovskite materials and LED applications, and outlining challenges for achieving the high-performance devices.

Non-toxic near-infrared light-emitting diodes

Harnessing cost-efficient printable semiconductor materials as near-infrared (NIR) emitters in light-emitting diodes (LEDs) is extremely attractive for sensing and diagnostics, telecommunications, and biomedical sciences. However, the most efficient NIR LEDs suitable for printable electronics rely on emissive materials containing precious transition metal ions (such as platinum), which have triggered concerns about their poor biocompatibility and sustainability. Here, we review and highlight the latest progress in NIR LEDs based on non-toxic and low-cost functional materials suitable for solution-processing deposition. Different approaches to achieve NIR emission from organic and hybrid materials are discussed, with particular focus on fluorescent and exciplex-forming host-guest systems, thermally activated delayed fluorescent molecules, aggregation-induced emission fluorophores, as well as lead-free perovskites. Alternative strategies leveraging photonic microcavity effects and surface plasmon resonances to enhance the emission of such materials in the NIR are also presented. Finally, an outlook for critical challenges and opportunities of non-toxic NIR LEDs is provided.

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.

Lead-Free Antimony Halide Perovskite with Heterovalent Mn2+ Doping

Lead toxicity is hindering the applications of conventional lead halide perovskites (PVKs), and antimony (Sb) is a promising nontoxic Pb alternative, showing huge potential in optoelectronic devices. Herein, pure and Mn-doped Cs₃Sb₂Cl₉ crystals are synthesized in a facile route and studied both experimentally and theoretically. All the pure and Mn-doped Cs₃Sb₂Cl₉ crystals show good crystallinity and similar crystal structures, exhibiting visible photoluminescence (PL) characteristics with emission peaks at 422 and 613 nm, respectively. Combined density functional theory (DFT) calculations and experimental analyses reveal that the structure of the host PVK compound Cs₃Sb₂Cl₉ is not influenced by the formation of [MnCl₆]^4- octahedra and that Mn 3d orbitals generate impurity states in the forbidden energy gap of Cs₃Sb₂Cl₉. Therefore, energy transfer from Cs₃Sb₂Cl₉ to Mn 3d states is observed, resulting in the d-d transition and bright red luminescence. Mn-doped Sb-based PVK can be utilized as a new platform for optoelectronic applications.

Focus on performance of perovskite light-emitting diodes

Perovskite-based optoelectronic devices, especially perovskite light-emitting diodes (PeLEDs) and perovskite solar cells, have recently attracted considerable attention. The National Renewable Energy Laboratory (NREL) chart inspires us to develop a counterpart for PeLEDs. In this study, we collect the record performance of PeLEDs including several new entries to address their latest external quantum efficiency (EQE), highest luminance, and stability status. We hope that these performance tables and future updated versions will show the frontiers of PeLEDs, assist researchers in capturing the overview of this field, identify the remaining challenges, and predict the promising research directions.

Layered perovskite materials: key solutions for highly efficient and stable perovskite solar cells

Metal halide perovskites having three-dimensional crystal structures are being applied successfully in various optoelectronic applications. To address their most challenging issues-instability and toxicity-without losing efficiency, lower-dimensional perovskites appear to be promising alternatives. Recently, two-dimensional (2D) perovskite solar cells have been developed exhibiting excellent photostability and moisture-stability, together with moderate device efficiency. This review summarizes the photophysical properties and operating mechanisms of 2D perovskites as well as recent advances in their applications in solar cell devices. Also presented is an agenda for the next-stage development of stable perovskite materials for solar cell applications, highlighting the issues of stability and toxicity that require further study to ensure commercialization.

Modulating Performance and Stability of Inorganic Lead-Free Perovskite Solar Cells via Lewis-Pair Mediation

Fully inorganic perovskites based on Bi³⁺ and Sb³⁺ are emerging as alternatives that overcome the toxicity and low stability of their Pb-based perovskite counterparts. Nevertheless, the thin film fabrication of Pb-free perovskites remains a struggle, with poor morphologies and incomplete conversions greatly inhibiting device performance. In this study, we modulated the crystallization of an all-inorganic dimer phase of a Sb perovskite (d-Cs₃Sb₂I₉) through gradual increase in the annealing temperature, accompanied by the use of Lewis bases for adduct formation. Here, the role of Lewis pairing in the crystallization of the resulting Pb-free Cs₃Sb₂I₉ thin films has been investigated. Both, "S-donor" (thiourea) and "O-donor" [N-methylpyrrolidone (NMP)] Lewis bases are examined for their abilities to form adducts with Cs⁺ and Sb³⁺ cations. Furthermore, density functional theory has been used to estimate the binding energies of these Lewis bases with the Cs₃Sb₂I₉ lattice. Temperature-dependent photoluminescence spectroscopy revealed the nature of the band gap of d-Cs₃Sb₂I₉. The efficiency of the resulting perovskite solar cells was enhanced to 1.8%, with excellent stability observed, when using NMP to form the adduct film. To the best of our knowledge, this is the best solar cell efficiency for the dimer phase of the inorganic Sb-based perovskite. The effects of both S- and O-donors are studied under various environmental stresses to reveal the stability responses of the devices.

Lead-Free Metal Halide Perovskites and Perovskite Derivatives as an Environmentally Friendly Emitter for Light-Emitting Device Applications

Recently, newly emerging lead halide perovskites have attracted great attention as a new class of light emitters in luminescent devices because of their superior photoluminescence quantum yield, adjustable emission wavelength, high charge-carrier transport ability, and low-temperature processing technique. However, the poor stability and lead toxicity of such materials severely restrict their practical applications and future commercialization. Therefore, recent efforts have been devoted to developing lead-free metal halide perovskites and their derivatives to address the above hurdles. In this Perspective, we first review the recent progress on the lead-free metal halide materials and their optical properties. We then discuss the stability issues of lead-free perovskites against heat, ultraviolet light, oxygen, and moisture. Further, we give a demonstration of the preliminary achievements and limitations in lead-free material-based light-emitting devices. Finally, we present current existing challenges and possible development opportunities in this field based on lead-free material systems.

Recent Advancements and Challenges for Low-Toxicity Perovskite Materials

Lead-based organic-inorganic hybrid perovskite materials have been developed for advanced optoelectronic applications. However, the toxicity of lead and the chemical instability of lead-based perovskite materials have so far been demonstrated to be an overwhelming challenge. The discovery of perovskite materials based on low-toxicity elements, such as Sn, Bi, Sb, Ge, and Cu, with superior optoelectronic properties provides alternative approaches to realize high-performance perovskite optoelectronics. In this review, recent advances in the aspects of low-toxicity perovskite solar cells, photodetectors, light-emitting diodes, and thermoelectric devices are highlighted. The antioxidation stability of metal cation and the crystallization process of the low-toxicity perovskite materials are discussed. In the last part, the outlook toward addressing various issues requiring further attention in the development of low-toxicity perovskite materials is outlined.

Lead-Free Perovskites for Lighting and Lasing Applications: A Minireview

Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which can be tuned through all visible range by a controllable change in chemical composition. To date, most of such materials contain lead atoms, which is one of the obstacles for their large-scale implementation. This disadvantage can be overcome via the substitution of lead with less toxic chemical elements, such as Sn, Bi, Yb, etc., and their mixtures. Herein, we summarized the scientific works from 2016 related to the lead-free perovskite materials with stress on the lasing and lighting applications. The synthetic approaches, chemical composition, and morphology of materials, together with the optimal device configurations depending on the material parameters are summarized with a focus on future challenges.