Ultrabroad Photoluminescence and Electroluminescence at New Wavelengths from Doped Organometal Halide Perovskites

Ultrabroad Near Infrared Emitting Perovskites

Phosphor converted light emitting diodes (pc-LEDs) have revolutionized solid-state white lighting by replacing energy-inefficient filament-based incandescent lamps. However, such a pc-LED emitting ultrabroad near-infrared (NIR) radiations still remains a challenge, primarily because of the lack of ultrabroad NIR emitting phosphors. To address this issue, we have prepared 2.5 % W4+-doped and 2.8 % Mo4+-doped Cs2Na0.95Ag0.05BiCl6 perovskites emitting ultrabroad NIR radiation with unprecedented spectral widths of 434 and 468 nm, respectively. Upon band-edge excitation, the soft lattice of the host exhibits broad self-trapped exciton (STE) emission covering NIR-I (700 nm), which then nonradiatively excites the dopants. The π ${\pi }$ -donor ligand Cl- reduces the energy of dopant d-d transitions emitting NIR-II with a peak at ~950 nm. Vibronic coupling broadens the dopant emission. The large spin-orbit coupling and local structural distortion might possibly enhance the dopant emission intensity, leading to an overall NIR photoluminescence quantum yield ~40 %. The composite of our ultrabroad NIR phosphors with biodegradable polymer polylactic acid could be processed into free-standing films and 3D printed structures. Large (170 × ${\times }$ 170 m m 2 ${m{m}^{2}}$ ), robust, and thermally stable 3D printed pc-LED panels emit ultrabroad NIR radiation, demonstrating NIR imaging applications.

Environmentally-Friendly Europium-Based Yellow Perovskite Nanocrystals with Near-Unit Efficiency for White LED

Recently, Mn2+-doped metal halide perovskites (MHPs) have been extensively studied as they can improve the photoluminescence quantum yield (PLQY) with minimal self-absorption. However, almost all of them with high efficiency are Pb/Cd-based toxic heavy metal perovskites, which seriously limits their commercial applications. To address the dual needs of high efficiency and environmental protection, this study proposes to incorporate Mn2+ into the environmentally friendly perovskite CsEuX3 (X = Cl/Br), and further increases PLQY to 96.9% through the codoping of Tb3+, which, to the best of our knowledge, is the highest reported value of all inorganic environmentally friendly perovskites in the visible light region. It is found that the codoping of Tb3+ can reduce the host defect density and enhance the crystal field strength around Mn2+, acting as an energy transfer bridge. Additionally, Mn2+/Tb3+-codoped CsEuX3-based white light-emitting diodes (WLEDs) with a high color rendering index (Ra = 91.2) demonstrate potential for lighting applications.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

Chemical Aspects of Halide Perovskite Nanocrystals

Halide perovskite nanocrystals (HPNCs) are currently among the most intensely investigated group of materials. Structurally related to the bulk halide perovskites (HPs), HPNCs are nanostructures with distinct chemical, optical, and electronic properties and significant practical potential. One of the keys to the effective exploitation of the HPNCs in advanced technologies is the development of controllable, reproducible, and scalable methods for preparation of materials with desired compositions, phases, and shapes and low defect content. Another important condition is a quantitative understanding of factors affecting the chemical stability and the optical and electronic properties of HPNCs. Here we review important recent developments in these areas. Following a brief historical prospective, we provide an overview of known chemical methods for preparation of HPNCs and approaches used to control their composition, phase, size, and shape. We then review studies of the relationship between the chemical composition and optical properties of HPNCs, degradation mechanisms, and effects of charge injection. Finally, we provide a short summary and an outlook. The aim of this review is not to provide a comprehensive summary of all relevant literature but rather a selection of highlights, which, in the subjective view of the authors, provide the most significant recent observations and relevant analyses.

Computational Modulation in Electronic Structures of Halide Perovskites via Element/Dopant/Phase

This study employs computational chemistry to investigate the electronic properties of halide perovskite materials, focusing on structural frameworks, elemental composition, surface engineering, and defect engineering. The tetragonal phase generally exhibits higher band gaps than the cubic phase due to conduction band differences, with LiPbCl3 showing the greatest band gap difference. The ionic radius of the A element influences band gaps for both phases, with Cs having the highest impact. Surface engineering significantly affects the electronic properties, and surface direction and composition play vital roles in determining band gaps. Defect engineering induces semiconducting-to-metallic transitions, impacting band gaps. Understanding these core variables is crucial for tailoring the electronic properties of halide perovskites for photovoltaic and optoelectronic applications.

Admirable stability achieved by ns2 ions Co-doping for all-inorganic metal halides towards optical anti-counterfeiting

Optical materials play a momentous role in anti-counterfeiting field, such as authentication, currency and security. The development of tunable optical properties and optical responses to a range of external stimuli is quite imperative for the growing demand of optical anti-counterfeiting technology. Metal halide perovskites have attracted much attention of researchers due to their excellent optical properties. In addition, co-doping methods have been gradually applied to the research of metal halide perovskites, by which more abundant luminescence phenomena can be introduced into the host perovskite. Herein, the ns² ions of bismuth (Bi³⁺) and antimony (Sb³⁺) ions co-doped zero-dimensional Cs₂SnCl₆ metal halide with an excitation-wavelength-dependent emission phenomenon is synthesized as an efficient multimodal luminescent material, the luminescence of which is tunable and covers a wide region of color. What's more, a dynamic dual-emission phenomenon is captured when the excitation wavelength changes from 320 nm to 420 nm for Cs₂SnCl₆:Bi_0.08Sb_0.12 crystals. Moreover, the Bi³⁺ and Sb³⁺ doped metal halide material shows great enhancement in solvent resistance and thermal stability compared to the pristine Cs₂SnCl₆. The admirable stability and distinguishable photoluminescence (PL) phenomenon of this all-inorganic metal halide has great potential to be applied in optical anti-counterfeiting technology. Furthermore, the co-doping method can accelerate the discovery of new luminescence phenomena in original metal halide perovskites.

Probing Chemical-Composition-Induced Heterostructures and Interfaces in Lead Halide Perovskites

Lead halide perovskites (LHP) are of great interest for their optoelectronic properties and photovoltaic applications. Various heterostructures are created in these materials to achieve favorable optical properties and improved stability at the interfaces during the fabrication of devices. Such heterostructures are often assumed to be formed based on the reactivity of precursors and are not directly probed. In this Feature Article, we report how various strategies have been employed in LHP thin films and nanocrystals (NCs) that generate heterostructures to boost their stability and photovoltaic (PV) efficiencies and how variable energy photoelectron spectroscopy (VEPES) can probe the chemical composition variation in heterostructured materials and interfaces. We specifically discussed the internal heterostructures of LHP NCs generated due to the surface chemistry and postsynthesis anion exchange followed by a detailed discussion of the heterostructures induced by the chemical composition (anion, cation, and degradation) of LHP thin films. The difficulties in determining heterostructures as well as the potential scope of the application of VEPES in unwrapping heterostructures in diverse materials are also discussed.

Tuning optical properties of CsPbBr3by mixing Nd3+trivalent lanthanide halide cations for blue light emitting devices

In recent years, significant progress has been made in the red and green perovskite quantum dots (PQDs) based light-emitting devices. However, a scarcity of blue-emitting devices that are extremely efficient precludes their research and development for optoelectronic applications. Taking advantage of tunable bandgaps of PQDs over the entire visible spectrum, herein we tune optical properties of CSPbBr₃by mixing Nd³⁺trivalent lanthanide halide cations for blue light-emitting devices. The CsPbBr₃PQDs doped with Nd³⁺trivalent lanthanide halide cations emitted strong photoemission from green into the blue region. By adjusting their doping concentration, a tunable wavelength from (515 nm) to (450 nm) was achieved with FWHM from (37.83 nm) to (16.6 nm). We simultaneously observed PL linewidth broadening thermal quenching of PL and the blue shift of the optical bandgap from temperature-dependent PL studies. The Nd³⁺cations into CsPbBr₃PQDs more efficiently reduced non-radiative recombination. As a result of the efficient removal of defects from PQDs, the photoluminescence quantum yield (PLQY) has been significantly increased to 91% in the blue-emitting region. Significantly, Nd³⁺PQDs exhibit excellent long-term stability against the external environment, including water, temperature, and ultraviolet light irradiation. Moreover, we successfully transformed Nd³⁺doped PQDs into highly fluorescent nanocomposites. Incorporating these findings, we fabricate and test a stable blue light-emitting LED with EL emission at (462 nm), (475 nm), and successfully produce white light emission from Nd³⁺doped nanocomposites with a CIE at (0.32, 0.34), respectively. The findings imply that low-cost Nd³⁺doped perovskites may be attractive as light converters in LCDs with a broad color gamut.

Air stable and highly efficient Bi3+-doped Cs2SnCl6 for blue light-emitting diodes

Cs2SnCl6 perovskite has recently attracted attention as a promising optoelectronic material owing to its better stability and reduced toxicity than its lead counterparts. However, its luminescence performance hardly satisfies the requirements. Hence, a series of Bi3+-doped Cs2SnCl6 (Cs2SnCl6:Bi3+) with enhanced luminescence were synthesized by a solution-phase route. The results show that the initial concentration of Sn2+ can adjust the nucleation density and the quality of the crystal nucleus growth, which will affect the Bi3+ doping amount, crystal morphology, and photophysical properties of Cs2SnCl6:Bi3+. Cs2SnCl6:Bi3+ shows excellent stability in the atmosphere with a photoluminescence (PL) of around 456 nm and a photoluminescence quantum yield (PLQY) of 31%. The luminescence performance results from [BiSn4+ 3+ + VCl] defects caused by the Bi3+ doping. The blue LED based on the Cs2SnCl6:Bi3+ phosphor exhibits a long life of about 120 h and a Commission Internationale de L'Eclairage (CIE) color coordinates of (0.14, 0.11). This work demonstrates a strategy for Bi-doped perovskites with good stability. This investigation will facilitate the development of Cs2SnCl6:Bi3+ for blue LED applications.

Bismuth Doping Alters Structural Phase Transitions in Methylammonium Lead Tribromide Single Crystals

We study the effects of bismuth doping on the crystal structure and phase transitions in single crystals of the perovskite semiconductor methylammonium lead tribromide, MAPbBr₃. By measuring the temperature-dependent specific heat capacity (C_p), we find that as the Bi doping increases, the phase transition assigned to the cubic to tetragonal phase boundary decreases in temperature. Furthermore, after doping we observe one phase transition between 135 and 155 K, in contrast to two transitions observed in the undoped single crystal. These results appear strikingly similar to previously reported effects of mechanical pressure on perovskite crystal structure. Using X-ray diffraction, we show that the lattice constant decreases as Bi is incorporated into the crystal, as predicted by density functional theory. We propose that bismuth substitutional doping on the lead site is dominant, resulting in Bi_Pb⁺ centers that induce compressive chemical strain that alters the crystalline phase transitions.

A first-principles study of the stability, electronic structure, and optical properties of halide double perovskite Rb2Sn1-xTexI6 for solar cell applications

Owing to their emerging role in solar cell technology, lead halide perovskites have aroused significant research interest in the recent past. However, due to its obvious toxicity, looking for a potential alternative to lead is becoming one of the most important pursuits in present times. We present our work based on density functional theory (DFT) investigating lead free defect perovskites (Rb₂Sn_1-xTe_xI₆ (0 ≤x≤ 1)). In particular, we explore the crystal structure, thermodynamic stability, electronic structure, and optical properties of Rb₂Sn_1-xTe_xI₆ (0 ≤x≤ 1) as a function of increasing Te concentration. Our results show that the Sn-Te alloyed perovskites exhibit considerable stability, a suitable band gap, small effective mass, and excellent light absorption. Especially, Rb₂Sn_0.75Te_0.25I₆ and Rb₂Sn_0.50Te_0.50I₆ have a direct band gap of 1.35 and 1.44 eV, respectively, which is highly favorable for use in a single-junction photovoltaic cell. We hope that our work will arouse the interest of experimental as well as theoretical scientists for synthesizing new materials and/or exploring the Sn-Te mix as a potential substitute for lead in photovoltaic materials.

Potassium-Induced Passivation of Deep Traps in Bismuth-Doped Hybrid Lead Bromide Perovskite Nanocrystals: Massive Amplification of Photoluminescence Quantum Yield

The low photoluminescence quantum yield of Bi³⁺-doped lead halide perovskite nanocrystals (NCs) is a big challenge to the scientific community. This makes them a weak candidate in the optoelectronics field in spite of their better stability than the pure lead analogue. Herein, the reason behind this reduction of quantum yield in hybrid mixed lead-bismuth bromide (MPBBr) NC is investigated and proposed to be due to ultrafast trapping transfer in the core of the NC, and not due to the surface trap states. Further, we have successfully boosted the quantum yield of MPBBr NC from 9% to 64% by passivating the deep traps within the crystal core by monovalent potassium ion doping. The stability of the developed Bi³⁺/K⁺-doped lead halide perovskite NC was found to be extremely high in atmospheric conditions, and this property is sustained up to 100 °C.

Highly Efficient Blue-Emitting CsPbBr3 Perovskite Nanocrystals through Neodymium Doping

Colloidal CsPbX3 (X = Br, Cl, and I) perovskite nanocrystals exhibit tunable bandgaps over the entire visible spectrum and high photoluminescence quantum yields in the green and red regions. However, the lack of highly efficient blue-emitting perovskite nanocrystals limits their development for optoelectronic applications. Herein, neodymium (III) (Nd3+) doped CsPbBr3 nanocrystals are prepared through the ligand-assisted reprecipitation method at room temperature with tunable photoemission from green to deep blue. A blue-emitting nanocrystal with a central wavelength at 459 nm, an exceptionally high photoluminescence quantum yield of 90%, and a spectral width of 19 nm is achieved. First principles calculations reveal that the increase in photoluminescence quantum yield upon doping is driven by an enhancement of the exciton binding energy due to increased electron and hole effective masses and an increase in oscillator strength due to shortening of the Pb-Br bond. Putting these results together, an all-perovskite white light-emitting diode is successfully fabricated, demonstrating that B-site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.

Down-Shifting and Anti-Reflection Effect of CsPbBr3 Quantum Dots/Multicrystalline Silicon Hybrid Structures for Enhanced Photovoltaic Properties

Over the past couple of decades, extensive research has been conducted on silicon (Si) based solar cells, whose power conversion efficiency (PCE) still has limitations because of a mismatched solar spectrum. Recently, a down-shifting effect has provided a new way to improve cell performances by converting ultraviolet (UV) photons to visible light. In this work, caesium lead bromide perovskite quantum dots (CsPbBr3 QDs) are synthesized with a uniform size of 10 nm. Exhibiting strong absorption of near UV light and intense photoluminescence (PL) peak at 515 nm, CsPbBr3 QDs show a potential application of the down-shifting effect. CsPbBr3 QDs/multicrystalline silicon (mc-Si) hybrid structured solar cells are fabricated and systematically studied. Compared with mc-Si solar cells, CsPbBr3 QDs/mc-Si solar cells have obvious improvement in external quantum efficiency (EQE) within the wavelength ranges of both 300 to 500 nm and 700 to 1100 nm, which can be attributed to the down-shifting effect and the anti-reflection property of CsPbBr3 QDs through the formation of CsPbBr3 QDs/mc-Si structures. Furthermore, a detailed discussion of contact resistance and interface defects is provided. As a result, the coated CsPbBr3 QDs are optimized to be two layers and the solar cell exhibits a highest PCE of 14.52%.

Antithermal Quenching of Luminescence in Zero-Dimensional Hybrid Metal Halide Solids

Zero-dimensional (0D) hybrid metal halides have emerged as a new generation of luminescent phosphors owing to their high radiative recombination rates, which, akin to their three-dimensional cousins, commonly demonstrate thermal quenching of luminescence. Here, we report on the finding of antithermal quenching of luminescence in 0D hybrid metal halides. Using (C₉NH₂₀)₂SnBr₄ single crystals as an example system, we show that 0D metal halides can demonstrate antithermal quenching of luminescence. A combination of experimental characterizations and first-principles calculations suggests that antithermal quenching of luminescence is associated with trap states introduced by structural defects in (C₉NH₂₀)₂SnBr₄. Importantly, we find that antithermal quenching of luminescence is not only limited to (C₉NH₂₀)₂SnBr₄ but also exists in other 0D metal halides. Our work highlights the important role of defects in impacting photophysical properties of hybrid metal halides and may stimulate new efforts to explore metal halides exhibiting antithermal quenching of luminescence at higher temperatures.

Enhanced Nonlinear Optical Coefficients of MAPbI3 Thin Films by Bismuth Doping

The poor photostability under ambient conditions of hybrid halide perovskites has hindered their recently explored promising nonlinear optical properties. Here, we show how Bi³⁺ can partially substitute Pb²⁺ homogeneously in the commonly studied MAPbI₃, improving both environmental stability and photostability under high laser irradiation. Bi content around 2 atom % produces thin films where the nonlinear refractive (n₂) and absorptive coefficients (β), which modify the refractive index (Δn) of the material with light fluence (I), increase up to factors of 4 and 3.5, respectively, compared to undoped MAPbI₃. Higher doping inhibits the nonlinear parameters; however, the samples show higher fluence damage thresholds. Thus, these results provide a road map on how MAPbI₃ can be engineered for practical cost-effective nonlinear applications by means of Bi doping, including optical limiting devices and multiple-harmonic generation into optoelectronics devices.

Incorporation of Nickel Ions to Enhance Integrity and Stability of Perovskite Crystal Lattice for High-Performance Planar Heterojunction Solar Cells

Enhancement of integrity and stability of crystal lattice are highly challenging for polycrystalline perovskite films. In this work, a strategy of incorporation of nickel (Ni) ions is presented to modulate the crystal structure of the CH₃NH₃PbI₃ perovskite film. A broad range of experimental characterizations reveal that the incorporation of Ni ions can substantially eliminate the intrinsic halide vacancy defects, since Ni ions have a strong preference for octahedral coordination with halide ions, resulting in significantly improved integrity and short-range order of crystal lattice. Moreover, it is also demonstrated that the stronger chemical bonding interaction between Ni ions and halide ions as well as organic group can improve the stability of the perovskite material. Simultaneously, the surface morphology of the perovskite thin film is also improved by the incorporation of nickel ions. As a result, a planar heterojunction perovskite solar cell incorporated with 1.5% Ni exhibits a power conversion efficiency of 18.82%, which is improved by 25% compared with 14.92% for the pristine device. Simultaneously, the device formed incorpration of 1.5% Ni shows remarkable stability with 90% of the initial efficiency after storage in an air environment for 800 h. The studies provide a new insight into metal-incorporated perovskite materials for various optoelectronic applications.

Photoluminescence spectral broadening, chirality transfer and amplification of chiral perovskite materials (R-X-p-mBZA)2PbBr4 (X = H, F, Cl, Br) regulated by van der Waals and halogen atoms interactions

We introduced halogen-substituted chiral molecules as A-site cations to synthesize a series of novel organic–inorganic hybrid 2D chiral perovskite materials (R-X-p-mBZA)₂PbBr₄ (X = H, F, Cl, Br; p: para-position; mBZA = α-methylbenzylamine).

Strategies to Improve Luminescence Efficiency of Metal-Halide Perovskites and Light-Emitting Diodes

Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted efforts to increase the LE of MHP emitters and PeLEDs. Within three and half years, PeLEDs have shown rapidly increased LE from external quantum efficiency ≈0.1% to ≈14.36%. Herein, the factors that limit the LE of PeLEDs are reviewed; the factors are characterized into the following groups: i) photophysical properties of MHP crystals, ii) morphological factors of MHP layers, and iii) problems caused by device architectures. Then, the strategies to overcome those luminescence-limiting factors in MHP emitters and PeLEDs are critically evaluated. Finally, research directions to further increase the LE of MHP emitters and the potential of MHPs as a core component in next-generation displays and solid-state lightings are suggested.

Deciphering the Ultrafast Nonlinear Optical Properties and Dynamics of Pristine and Ni-Doped CsPbBr3 Colloidal Two-Dimensional Nanocrystals

While the unabated race persists in achieving record efficiencies in solar cells and other photonic/optoelectronic devices using lead halide perovskite absorbers, a comprehensive picture of the correlated third-order nonlinear optical (NLO) properties is yet to be established. The present study is aimed at deciphering the role of dopants in multiphoton absorption properties of intentionally engineered CsPbBr₃ colloidal nanocrystals (NCs). The charge separation of the plasmon-semiconductor conduction band owing to the hot electron transfer at the interface was demystified using the dynamics of the bleached spectral data from femtosecond (fs) transient absorption spectroscopy with broadband capabilities. The NLO properties studied through the fs Z-scan technique revealed that Ni-doped CsPbBr₃ NCs exhibited strong third-order NLO susceptibility of ∼10^-10 esu. The exotic photophysical phenomena in these pristine and Ni-doped CsPbBr₃ colloidal two-dimensional (2D) NCs reported herein are believed to provide the avenues to address the critical variables involved in the structural differences and their correlated optoelectronic properties.

Bismuth Halide Perovskite-Like Materials: Current Opportunities and Challenges

Metal halide perovskites have recently emerged as promising photovoltaic materials for application in solar cells with high power conversion efficiencies exceeding 23 %. In the years since such high efficiencies have been attained, investigations have mainly focused on the state-of-the-art 3 D Pb-based halide perovskite materials. However, the high toxicity of Pb and intrinsic instability of the pristine perovskite materials have become great obstacles to their industrial application and commercialization. To address these serious issues, it is imperative to explore low-toxicity metal halide perovskites or their derivatives to substitute Pb-based materials for better future development. Currently, Bi-based halide perovskite-like materials are attracting increased interest as environmentally friendly alternatives for photovoltaic applications. This Concept highlights recent advances of Bi-based halide perovskite-like materials in terms of understanding and modifying their fundamental properties and related device performance, with a focus on current challenges, opportunities for future development, and diversification of device applications.

Ultrafast, Self-Driven, and Air-Stable Photodetectors Based on Multilayer PtSe2/Perovskite Heterojunctions

We report on the large-scale synthesis of polycrystalline multilayer PtSe₂ film with typical semimetallic characteristics. With the availability of the large-area film, we constructed a heterojunction composed of multilayer PtSe₂ and Cs-doped FAPbI₃, which can function as a self-driven photodetector in a broadband wavelength from the ultraviolet to the near-infrared region. Further photoresponse analysis revealed that the heterojunction device showed outstanding photosensitive characteristics with a large I_light/ I_dark ratio of 5.7 × 10³, high responsivity of 117.7 mA W^-1, and decent specific detectivity of 2.91 × 10¹² Jones at zero bias. More importantly, the rise/fall times were estimated to be 78/60 ns, rendering our device the fastest device among perovskite-2D photodetectors reported to date. In addition, it was also observed that the PtSe₂/perovskite photodetector can almost retain its photoresponse properties after storage in ambient conditions for 3 weeks. This study suggests the potential of the present PtSe₂/perovskite heterojunction for future air-stable ultrafast photodetecting applications.

CH3NH3Pb1−xEuxI3 mixed halide perovskite for hybrid solar cells: the impact of divalent europium doping on efficiency and stability

The crucial role of the impact of divalent europium doping in perovskite solar cells is investigated in this work.

Aluminum-Doped Cesium Lead Bromide Perovskite Nanocrystals with Stable Blue Photoluminescence Used for Display Backlight

Bright and stable blue emitters with narrow full-width at half-maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al3+) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead-halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion-exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red-emitting CdSe@ZnS NCs result in UV-pumped white light-emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU-R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low-cost, earth-abundant, solution-processable Al-doped perovskite NCs can be promising candidate materials for blue down-conversion layer in backlit displays.

Inhibition of Zero Drift in Perovskite-Based Photodetector Devices via [6,6]-Phenyl-C61-butyric Acid Methyl Ester Doping

Zero drift can severely deteriorate the stability of the light-dark current ratio, detectivity, and responsivity of photodetectors. In this paper, the effects of a [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-doped perovskite-based photodetector device on the inhibition of zero drift under dark state are discussed. Two kinds of photodetectors (Au/CH₃NH₃PbI_xCl_3-x/Au and Au/CH₃NH₃PbI_xCl_3-x:PCBM/Au) were prepared, and the materials and photodetector devices were measured by scanning electron microscopy, X-ray diffraction, photoluminescence, ultraviolet absorption spectra, and current-voltage and current-time measurements. It was found that similar merit parameters, including light-dark current ratio (∼10²), detectivity (∼10¹¹ Jones), and responsivity were obtained for these two kinds of photodetectors. However, the drift of Au/CH₃NH₃PbI_xCl_3-x:PCBM/Au devices is negligible, while a drift of ∼0.2 V exists in Au/CH₃NH₃PbI_xCl_3-x/Au devices. A new model is proposed based on the hindering theory of ion (vacancy) migration, and it is believed that the dopant PCBM can hinder the ion (vacancy) migration of perovskite materials to suppress the phenomenon of zero drift in perovskite-based photodetectors.

Electrochemical Doping of Halide Perovskites with Ion Intercalation

Halide perovskites have recently been investigated for various solution-processed optoelectronic devices. The majority of studies have focused on using intrinsic halide perovskites, and the intentional incoporation of dopants has not been well explored. In this work, we discovered that small alkali ions, including lithium and sodium ions, could be electrochemically intercalated into a variety of halide and pseudohalide perovskites. The ion intercalation caused a lattice expansion of the perovskite crystals and resulted in an n-type doping of the perovskites. Such electrochemical doping improved the conductivity and changed the color of the perovskites, leading to an electrochromism with more than 40% reduction of transmittance in the 450-850 nm wavelength range. The doped perovskites exhibited improved electron injection efficiency into the pristine perovskite crystals, resulting in bright light-emitting diodes with a low turn-on voltage.

Perovskite/Poly(3-hexylthiophene)/Graphene Multiheterojunction Phototransistors with Ultrahigh Gain in Broadband Wavelength Region

Organometal halide perovskite materials have attracted much attention recently for their excellent optoelectronic properties. Here, we report an ultrasensitive phototransistor based on the multiheterojunction of CH₃NH₃PbI_3-xCl_x perovskite/poly(3-hexylthiophene)/graphene for the first time. Since the photoexcited electrons and holes are effectively separated by the poly(3-hexylthiophene) layer, high-density electrons are trapped in the perovskite layer, leading to a strong photogating effect on the underlying graphene channel. The phototransistor demonstrates an unprecedented ultrahigh responsivity of ∼4.3 × 10⁹ A/W and a gain approaching 10¹⁰ electrons per photon, respectively. More importantly, the device is sensitive in a broadband wavelength region from ultraviolet to near-infrared, which has not yet been achieved with other perovskite photodetectors. It is expected that the novel perovskite phototransistor will find promising applications as photodetection and imaging devices in the future.

Controlling red upconversion luminescence in Gd2O3:Yb3+–Er3+nanoparticles by changing the different atmosphere

Upconversion luminescence properties were investigated by emission intensityvs.excitation power (double logarithmic relationship) and temperature dependent emission spectroscopy.