A high-performance metal halide perovskite-based laser-driven display.

Ternary and quaternary semiconductor quantum dots (QDs) are candidates for cadmium-free alternatives. Among these, semiconductors containing elements from groups 11, 13, and 16 (i.e., I–III–VI2) are attracting increasing attention since they are direct semiconductors whose bandgap energies in the bulk state are tunable between visible and near infrared. The quaternary system of alloys consisting of silver indium sulfide (AgInS2; bandgap energy: Eg = 1.8 eV) and silver gallium sulfide (AgGaS2; Eg = 2.4 eV) (i.e., Ag[InxGa1−x]S2 (AIGS)) enables bandgap tuning over a wide range of visible light. However, the photoluminescence (PL) quantum yield (10–20%) of AIGS QDs is significantly lower than that of AgInS2 (60–70%). The present study investigates how to improve the PL quantum yield of AIGS QDs via surface ligand engineering. Firstly, the use of a mixture of oleic acid and oleylamine, instead of only oleylamine, as the solvent for the QD synthesis was attempted, and a threefold improvement of the PL quantum yield was achieved. Subsequently, a post-synthetic ligand exchange was performed. Although the addition of alkylphosphine, which is known as an L-type ligand, improved the PL efficiency only by 20%, the use of metal halides, which are categorized as Z-type ligands, demonstrated a twofold to threefold improvement of the PL quantum yield, with the highest value reaching 73.4%. The same procedure was applied to the band-edge emitting core/shell-like QDs that were synthesized in one batch based on our previous findings. While the as-prepared core/shell-like QDs exhibited a PL quantum yield of only 9%, the PL quantum yield increased to 49.5% after treatment with metal halides.

Metal halide perovskites have been investigated for the next-generation light-emitting materials because of their advantages such as high photoluminescence quantum yield (PLQY), excellent color purity, and facile color tunability. Recently, red- and green-emissive perovskite light-emitting diodes (PeLEDs) have shown an external quantum efficiency (EQE) of over 20%, whereas there is still room for improvement for blue emissive PeLEDs. By controlling the halide compositions of chloride (Cl−) and bromide (Br−), the bandgap of perovskites can be easily tuned for blue emission. However, halide segregation easily occurrs in the mixed-halide perovskite under light irradiation and LED operation because of poor phase stability. Here, we explore the effect of A-site cation engineering on the phase stability of the mixed-halide perovskites and find that a judicious selection of low dipole moment A cation (formamidinium or cesium) suppresses the halide segregation. This enables efficient bandgap tuning and electroluminescence stability for sky blue emissive PeLEDs over the current density of 15 mA/cm2.

Metal halide perovskites have emerged as a promising new class of layered semiconductor material for light‐emitting and photovoltaic applications owing to their outstanding optical and optoelectronic properties. In nanocrystalline form, these layered perovskites exhibit extremely high photoluminescence quantum yields (PLQYs) and show quantum confinement effects analogous to conventional semiconductors when their dimensions are reduced to sizes comparable to their respective exciton Bohr radii. The reduction in size leads to strongly blueshifted photoluminescence and large exciton binding energies up to several hundreds of meV. This not only makes them interesting for optoelectronic devices, but also enables complex architectures based on cascaded energy transfer. Here, an overview of the current state‐of‐the‐art of quantum confinement effects in perovskite nanocrystals is provided, with a focus on synthetic strategies and resulting optical properties, characterization methods, and emerging applications.

This review surveys recent advances in employing photoluminescence quantum yield (PLQY) as a quantitative probe in perovskite solar cells (PSCs), highlighting its unique ability to diagnose interfacial nonradiative recombination, reconstruct quasi‐Fermi‐level splitting (QFLS), and anticipate efficiency limits. After presenting the theoretical framework that converts PLQY into QFLS so that it can be directly benchmarked against the device open‐circuit voltage (), we clarify the complementarity between PLQY and conventional time‐resolved photoluminescence. Representative case studies then illustrate how PLQY pinpoints recombination losses at the perovskite/electron‐transport‐layer and perovskite/hole‐transport‐layer interfaces and how targeted passivation strategies simultaneously enhance PLQY, QFLS, and overall device efficiency. The review also discusses how illumination intensity, excitation wavelength, temperature, and humidity influence PLQY measurements and argues that coupling high‐throughput, in situ PLQY mapping with machine‐learning algorithms promises to accelerate the discovery of highly efficient, lead‐free, and stable perovskite materials and devices.

Highly luminescent CsPbX3/PMMA (X=Br, I) composites with improved stability for full-color Micro-LED displays

The development of water-stable metal halide perovskites (MHPs) presents a significant challenge for advanced materials and their application in electrochemical energy conversion and storage. Understanding the electronic structure of MHPs, considering electrocatalysis under an aqueous electrolyte, is essential for its widespread applications. Also, considerable efforts have been devoted to enhancing water stability through ligand passivation, compositional engineering, and surface encapsulation strategies. However, the long-term stability and charge transport properties of these materials may still fall short of expectations. Therefore, synthesizing intrinsically stable MHPs is crucial for their use in energy conversion and storage applications. Numerous comprehensive reviews have addressed the optical properties, regulation of electronic properties, and stability of MHPs. This review aims to provide an in-depth analysis of electronic structure and properties, followed by theoretical and experimental evidence of degradation mechanisms in aqueous media of various organic and inorganic MHPs. Subsequently, we also highlight the perspectives and progress in MHPs designing strategies and the synthesis of intrinsically water-stable perovskites to overcome stability challenges. By connecting the degradation dynamics with synthesis approaches for water-stable MHPs, this report paves the way for their application in electrocatalysis and energy storage devices.

Lanthanide-doped Mn2+-based perovskite-like single crystals: Switching on highly thermal-stable near-infrared emission and LED device

Recently, metal-halide perovskite nanocrystals (NCs) have shown major development and have attracted substantial interest in a wide range of applications, such as light-emitting diodes (LEDs), solar cells, lasers, and photodetectors due to their attractive properties, such as superior PL emission, a wider range of color tunability, narrow emission spectra, better color purity, low cost, easy solution-processability, and so on. In the past, many color-converting materials, such as III-nitrides, organics, polymers, metal chalcogenides, were investigated for solid-state lighting (SSL) white light-emitting diodes (WLEDs). Still, they suffer from issues such as low stability, low color rendering index (CRI), high correlated color temperature (CCT), low luminous efficiency (LE), and high cost. In this sense, metal-halide perovskite NCs exhibit a better color gamut compared with conventional lighting sources, and production costs are comparatively cheaper. Such materials may offer an upcoming substitute for future color-converting WLEDs. In this review, we discuss the metal halide perovskite NCs and their synthesis protocols. Then we elaborate on the recent progress of halide perovskite NCs as a conversion layer in the application of WLEDs.

Low‐dimensional lead‐based metal halide perovskites (MHPs) have many exceptional photoelectric capabilities thanks to the 6 s2 electron structure of lead ion (Pb2+). Pb2+′s toxicity, however, has prevented its widespread development and use. Finding ions in the valence layer that have a comparable electrical structure thus makes sense as Pb2+ replacements. In this work, all inorganic zero‐dimensional (0D) Cs3BiCl6 single crystal was synthesized by the anti‐solvent crystallization method. There is no obvious photoluminescence (PL) phenomenon for Cs3BiCl6 at room temperature (RT). It is found that the extremely strong exciton‐phonon interaction leads to seriously non‐radiative recombination. After doping with Sb3+, Cs3BiCl6: Sb achieved broadband emission with a significant Stokes shift, the photoluminescence quantum yield (PLQY) up to 15.85 %, which has a microsecond PL decay lifetime and excellent environmental stability. Systematic spectroscopic characterizations unveil the PL mechanism of Cs3BiCl6: Sb is self‐trapped excitons (STEs) emission, and theoretical calculation revealed the indirect bandgap properties of Cs3BiCl6 and Cs3BiCl6: Sb.

Metal halide perovskite nanoplatelets (NPls) exhibit attractive optical properties as a result of quantum and dielectric confinement effects. Their strong and narrow photoluminescence (PL), tunable over the entire visible spectral range, makes them highly promising for light-emission and lasing applications. In metal halide perovskites, partial cation substitution serves as an additional tool for fine-tuning their structure and optical properties. While A-site cation substitution has been successfully used for perovskite nanocrystals, its application to their NPl counterparts has not yet been widely addressed. In this study, we demonstrate that sufficient surface passivation is required to be performed prior to A-site cation exchange in CsPbI3 perovskite NPls by treatment with ZnI2 and oleylamine, enabling efficient A-site cation substitution with both smaller (rubidium, Rb+) and larger (formamidinium, FA+) cations. This allowed us to tune the PL peak position of NPls over a broad spectral range of 590-630 nm. In particular, mixed-cation Cs1-xFAxPbI3 (x = 0.68-0.87) NPls exhibited narrow (full width at half maximum ∼ 25 nm) and efficient (PL quantum yield ∼ 90%) pure-red emission at 620-626 nm, making them promising candidates for light emission applications. We have furthermore demonstrated that the partial A-site substitution of (Cs+) with organic (FA+) cations enhanced the nonlinear optical responses of Cs1-xFAxPbI3 NPls, whose TPA cross-section increased up to 3.85 × 106 GM, positioning them as promising materials for nonlinear optical applications.

Achieving highly fluorescent and stable perovskite materials has remained a significant challenge in recent years. While several works have reported high photoluminescence and moderate stability in various perovskite systems, this study reports for the first time a photoluminescence quantum yield of 100% with exceptional stability through lanthanide doping of the Cs2Na0.9Ag0.1In0.95Bi0.05Cl6 double perovskite. The lanthanide doping process resulted in a strong and efficient broadband self-trapped exciton (STE) emission. Remarkably, the Yb3+-doped Cs2Na0.9Ag0.1In0.95Bi0.05Cl6, and Er3+-doped Cs2Na0.9Ag0.1In0.95Bi0.05Cl6 sample exhibited a warm-white light emission with near-unity PLQY of 99.8% and 100%, respectively, while the pristine sample delivered a 2.3% PLQY only. Structural characterization confirmed the high purity of the samples with near-stoichiometric composition of the materials, with no detectable evidence for secondary phases. The samples maintained their superior emission properties over extended periods of testing. When assembled into a white-light-emitting diode (WLED), the materials generated a strong broadband luminescence (EL) with an excellent color rendering index (CRI) of 91.3 and a correlated color temperature (CCT) of 2826 K, achieving a highly efficient and stable performance. This study highlights that lead-free double perovskites can be reliable and highly efficient materials for commercial LED devices, paving the way for a more sustainable and efficient lighting solution.

Metal halide perovskites are promising for next-generation flexible photodetectors owing to their low-temperature solution processability, mechanical flexibility, and excellent photoelectric properties. However, the defects and notorious ion migration in polycrystalline metal halide perovskites often lead to high and unstable dark current, thus deteriorating their detection limit and long-term operations. Here, we propose an electrical field modulation strategy to significantly reduce the dark current of metal halide perovskites-based flexible photodetector more than 1000 times (from ~5 nA to ~5 pA). Meanwhile, ion migration in metal halide perovskites is effectively suppressed, and the metal halide perovskites-based flexible photodetector shows a long-term continuous operational stability (~8000 s) with low signal drift (~4.2 × 10−4 pA per second) and ultralow dark current drift (~1.3 × 10−5 pA per second). Benefitting from the electrical modulation strategy, a high signal-to-noise ratio wearable photoplethysmography sensor and an active-matrix photodetector array for weak light imaging are successfully demonstrated. This work offers a universal strategy to improve the performance of metal halide perovskites for wearable flexible photodetector and image sensor applications.

Metal halide perovskites are an important class of emerging semiconductors. Their charge carrier dynamics is poorly understood due to limited knowledge of defect physics and charge carrier recombination mechanisms. Nevertheless, classical ABC and Shockley-Read-Hall (SRH) models are ubiquitously applied to perovskites without considering their validity. Herein, an advanced technique mapping photoluminescence quantum yield (PLQY) as a function of both the excitation pulse energy and repetition frequency is developed and employed to examine the validity of these models. While ABC and SRH fail to explain the charge dynamics in a broad range of conditions, the addition of Auger recombination and trapping to the SRH model enables a quantitative fitting of PLQY maps and low-power PL decay kinetics, and extracting trap concentrations and efficacies. However, PL kinetics at high power are too fast and cannot be explained. The proposed PLQY mapping technique is ideal for a comprehensive testing of theories and applicable to any semiconductor.

A series of four perylene diimide (PDI) chromophores were prepared with increasing steric bulk on the imide substituents with the aim of retarding the effect of concentration quenching on photoluminescence, commonly observed with these dyes. Spectroscopic investigations of the compounds in dilute solution confirmed that the photophysical properties of the PDI core chromophore were not perturbed by the bulky substituents. Solid film samples containing the PDI compounds at various concentrations dispersed in a poly(methyl methacrylate) (PMMA) matrix were examined and compared to amorphous neat films as well as crystalline samples. The PDI compounds containing di-tert-butylphenyl (bPDI-3) and trityl (bPDI-4) substituents showed near unity photoluminescence quantum yield (PLQY) up to 20 mM in PMMA compared to 10% PLQY for the reference compound (bPDI-1) without molecular insulation. Surprisingly, high concentrations (>40 mM) of a phenyl-substituted PDI compound (bPDI-2) with moderate molecular insulation form...

The outstanding emission of halide perovskites make them ideal candidates for white emission light-emitting diodes (LEDs) for lighting applications. However, many perovskites contain toxic or scarce elements and have unsatisfactory stability. Here, we report a target-driven approach, based on active learning (AL) techniques, to discover halide perovskites suitable for commercial LED applications. Based on the similarity between halide and oxide perovskites, a model trained on an oxide perovskite dataset plus six AL-selected halide perovskites exhibited excellent performance for photoluminescence quantum yield (PLQY) predictions of oxide and halide perovskites. The model proposed a strong relationship between ionic radii and PLQY, postulated to be due to the self-trap excitons derived from the Jahn-Teller deformation. A novel halide perovskite phosphor, Cs4Zn(Bi0.85Sb0.15)2Cl12:0.01Mn, was designed and synthesized with the aid of the model. It exhibited an 88 % PLQY and outstanding thermal and luminescent stability. A simple white LED was fabricated from this material, exemplifying its commercial potential. This study demonstrates how machine learning techniques can accelerate discovery of next-generation phosphors for high performance single emitter-based white-light emitting devices.