Facile Synthesis,Silanization, and Biodistribution of Biocompatible Quantum Dots

A facile strategy for the synthesis of silica‐coated quantum dots (QDs) for in vivo imaging is reported. All the QD synthesis and silanization steps are conducted in water and methanol under mild conditions without involving any organometallic precursors or high‐temperature, oxygen‐free environments. The as‐prepared silica‐coated QDs possess high quantum yields and are extremely stable in mouse serum. In addition, the silanization method developed here produces nanoparticles with small sizes that are difficult to achieve via conventional silanization methods. The silica coating helps to prevent the exposure of the QD surface to the biological milieu and therefore increases the biocompatibility of QDs for in vivo applications. Interestingly, the silica‐coated QDs exhibit a different biodistribution pattern from that of commercially available Invitrogen QD605 (carboxylate) with a similar size and emission wavelength. The Invitrogen QD605 exhibits predominant liver (57.2% injected dose (ID) g^?1) and spleen (46.1% ID g^?1) uptakes 30 min after intravenous injection, whereas the silica‐coated QDs exhibit much lower liver (16.2% ID g^?1) and spleen (3.67% ID g^?1) uptakes but higher kidney uptake (8.82% ID g^?1), blood retention (15.0% ID g^?1), and partial renal clearance. Overall, this straightforward synthetic strategy paves the way for routine and customized synthesis of silica‐coated QDs for biological use.     

Ultrathin,Core–Shell Structured SiO2 Coated Mn2+‐Doped Perovskite Quantum Dots for Bright White Light‐Emitting Diodes

All‐inorganic semiconductor perovskite quantum dots (QDs) with outstanding optoelectronic properties have already been extensively investigated and implemented in various applications. However, great challenges exist for the fabrication of nanodevices including toxicity, fast anion‐exchange reactions, and unsatisfactory stability. Here, the ultrathin, core–shell structured SiO₂ coated Mn²⁺ doped CsPbX₃ (X = Br, Cl) QDs are prepared via one facile reverse microemulsion method at room temperature. By incorporation of a multibranched capping ligand of trioctylphosphine oxide, it is found that the breakage of the CsPbMnX₃ core QDs contributed from the hydrolysis of silane could be effectively blocked. The thickness of silica shell can be well‐controlled within 2 nm, which gives the CsPbMnX₃@SiO₂ QDs a high quantum yield of 50.5% and improves thermostability and water resistance. Moreover, the mixture of CsPbBr₃ QDs with green emission and CsPbMnX₃@SiO₂ QDs with yellow emission presents no ion exchange effect and provides white light emission. As a result, a white light‐emitting diode (LED) is successfully prepared by the combination of a blue on‐chip LED device and the above perovskite mixture. The as‐prepared white LED displays a high luminous efficiency of 68.4 lm W^?1 and a high color‐rendering index of Ra = 91, demonstrating their broad future applications in solid‐state lighting fields.     

Room‐Temperature Triple‐Ligand Surface Engineering Synergistically Boosts Ink Stability,Recombination Dynamics,and Charge Injection toward EQE‐11.6% Perovskite QLEDs

Developing low‐cost and high‐quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light‐emitting diodes (LEDs) is crucial for the next‐generation ultra‐high‐definition flexible displays. Here, there is a report on a room‐temperature triple‐ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward “ideal” perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD‐based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A‐site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr₃ QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W^?1, respectively, which are the most‐efficient perovskite QLEDs with colloidal CsPbBr₃ QDs as emitters up to now. These results demonstrate that the as‐obtained QD inks have a wide range application in future high‐definition QD displays and high‐quality lightings.     

Efficient Red Perovskite Light‐Emitting Diodes Based on Solution‐Processed Multiple Quantum Wells

This paper reports a facile and scalable process to achieve high performance red perovskite light‐emitting diodes (LEDs) by introducing inorganic Cs into multiple quantum well (MQW) perovskites. The MQW structure facilitates the formation of cubic CsPbI₃ perovskites at low temperature, enabling the Cs‐based QWs to provide pure and stable red electroluminescence. The versatile synthesis of MQW perovskites provides freedom to control the crystallinity and morphology of the emission layer. It is demonstrated that the inclusion of chloride can further improve the crystallization and consequently the optical properties of the Cs‐based MQW perovskites, inducing a low turn‐on voltage of 2.0 V, a maximum external quantum efficiency of 3.7%, a luminance of ≈440 cd m^?2 at 4.0 V. These results suggest that the Cs‐based MQW LED is among the best performing red perovskite LEDs. Moreover, the LED device demonstrates a record lifetime of over 5 h under a constant current density of 10 mA cm^?2. This work suggests that the MQW perovskites is a promising platform for achieving high performance visible‐range electroluminescence emission through high‐throughput processing methods, which is attractive for low‐cost lighting and display applications.     

How Effective is Plasmonic Enhancement of Colloidal Quantum Dots for Color‐Conversion Light‐Emitting Devices?

Enhancing the fluorescence intensity of colloidal quantum dots (QDs) in case of color‐conversion type QD light‐emitting devices (LEDs) is very significant due to the large loss of QDs and their quantum yields during fabrication processes, such as patterning and spin‐coating, and can therefore improve cost‐effectiveness. Understanding the enhancement process is crucial for the design of metallic nanostructure substrates for enhancing the fluorescence of colloidal QDs. In this work, improved color conversion of colloidal green and red QDs coupled with aluminum (Al) and silver (Ag) nanodisk (ND) arrays designed by in‐depth systematic finite‐difference time domain simulations of excitation, spontaneous emission, and quantum efficiency enhancement is reported. Calculated results of the overall photoluminescence enhancement factor in the substrate of 500 × 500 µm² size are 2.37‐fold and 2.82‐fold for Al ND‐green QD and Ag ND‐red QD structures, respectively. Experimental results are in good agreement, showing 2.26‐fold and 2.66‐fold enhancements for Al ND and Ag ND structures. Possible uses of plasmonics in cases such as white LED and total color conversion for possible display applications are discussed. The theoretical treatments and experiments shown in this work are a proof of principle for future studies of plasmonic enhancement of various light‐emitting materials.     

Stability of Quantum Dots,Quantum Dot Films,and Quantum Dot Light‐Emitting Diodes for Display Applications

Quantum dots (QDs) are being highlighted in display applications for their excellent optical properties, including tunable bandgaps, narrow emission bandwidth, and high efficiency. However, issues with their stability must be overcome to achieve the next level of development. QDs are utilized in display applications for their photoluminescence (PL) and electroluminescence. The PL characteristics of QDs are applied to display or lighting applications in the form of color‐conversion QD films, and the electroluminescence of QDs is utilized in quantum dot light‐emitting diodes (QLEDs). Studies on the stability of QDs and QD devices in display applications are reviewed herein. QDs can be degraded by oxygen, water, thermal heating, and UV exposure. Various approaches have been developed to protect QDs from degradation by controlling the composition of their shells and ligands. Phosphorescent QDs have been protected by bulky ligands, physical incorporation in polymer matrices, and covalent bonding with polymer matrices. The stability of electroluminescent QLEDs can be enhanced by using inorganic charge transport layers and by improving charge balance. As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.     

Efficient and Tunable Electroluminescence from In Situ Synthesized Perovskite Quantum Dots

Semiconductor quantum dots (QDs) are among the most promising next‐generation optoelectronic materials. QDs are generally obtained through either epitaxial or colloidal growth and carry the promise for solution‐processed high‐performance optoelectronic devices such as light‐emitting diodes (LEDs), solar cells, etc. Herein, a straightforward approach to synthesize perovskite QDs and demonstrate their applications in efficient LEDs is reported. The perovskite QDs with controllable crystal sizes and properties are in situ synthesized through one‐step spin‐coating from perovskite precursor solutions followed by thermal annealing. These perovskite QDs feature size‐dependent quantum confinement effect (with readily tunable emissions) and radiative monomolecular recombination. Despite the substantial structural inhomogeneity, the in situ generated perovskite QDs films emit narrow‐bandwidth emission and high color stability due to efficient energy transfer between nanostructures that sweeps away the unfavorable disorder effects. Based on these materials, efficient LEDs with external quantum efficiencies up to 11.0% are realized. This makes the technologically appealing in situ approach promising for further development of state‐of‐the‐art LED systems and other optoelectronic devices.     

Synergies of Electrochemical Metallization and Valance Change in All‐Inorganic Perovskite Quantum Dots for Resistive Switching

The in‐depth understanding of ions' generation and movement inside all‐inorganic perovskite quantum dots (CsPbBr₃ QDs), which may lead to a paradigm to break through the conventional von Neumann bottleneck, is strictly limited. Here, it is shown that formation and annihilation of metal conductive filaments and Br^? ion vacancy filaments driven by an external electric field and light irradiation can lead to pronounced resistive‐switching effects. Verified by field‐emission scanning electron microscopy as well as energy‐dispersive X‐ray spectroscopy analysis, the resistive switching behavior of CsPbBr₃ QD‐based photonic resistive random‐access memory (RRAM) is initiated by the electrochemical metallization and valance change. By coupling CsPbBr₃ QD‐based RRAM with a p‐channel transistor, the novel application of an RRAM–gate field‐effect transistor presenting analogous functions of flash memory is further demonstrated. These results may accelerate the technological deployment of all‐inorganic perovskite QD‐based photonic resistive memory for successful logic application.     

Enhancement of Fluorescence Emission for Tricolor Quantum Dots Assembled in Polysiloxane toward Solar Spectrum‐Simulated White Light‐Emitting Devices

Commercial white light‐emitting diodes (LEDs) have the undesirable characteristics of blue‐rich emission and low color rendering index (CRI), while the constituent quantum dots (QDs) suffer from aggregation‐induced fluorescence quenching and poor stability. Herein, a strategy is developed to assemble tricolor QDs into a polysiloxane matrix using a polymer‐mediated hybrid approach whereby the hybrid composite exhibits a significant enhancement of aggregation‐dispersed emission, outstanding photostability, high thermal stability, and outstanding fluorescence recovery. Using the as‐prepared hybrid fluorescent materials, the fabricated LEDs exhibit solar spectrum‐simulated emission with adjustable Commission Internationale de L'Eclairage coordinates, correlated color temperature, and a recorded CRI of 97. Furthermore, they present no ultraviolet emission and weak blue emission, thus indicating an ideal healthy and high‐CRI white LED lighting source.     

Cosensitized Quantum Dot Solar Cells with Conversion Efficiency over 12%

The improvement of sunlight utilization is a fundamental approach for the construction of high‐efficiency quantum‐dot‐based solar cells (QDSCs). To boost light harvesting, cosensitized photoanodes are fabricated in this work by a sequential deposition of presynthesized Zn–Cu–In–Se (ZCISe) and CdSe quantum dots (QDs) on mesoporous TiO₂ films via the control of the interactions between QDs and TiO₂ films using 3‐mercaptopropionic acid bifunctional linkers. By the synergistic effect of ZCISe‐alloyed QDs with a wide light absorption range and CdSe QDs with a high extinction coefficient, the incident photon‐to‐electron conversion efficiency is significantly improved over single QD‐based QDSCs. It is found that the performance of cosensitized photoanodes can be optimized by adjusting the size of CdSe QDs introduced. In combination with titanium mesh supported mesoporous carbon as a counterelectrode and a modified polysulfide solution as an electrolyte, a champion power conversion efficiency up to 12.75% (V_oc = 0.752 V, J_sc = 27.39 mA cm^?2, FF = 0.619) is achieved, which is, as far as it is known, the highest efficiency for liquid‐junction QD‐based solar cells reported.     

Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH3NH3PbI3

The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH₃NH₃PbI₃/SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH₃NH₃PbI₃, SCs using CH₃NH₃PbI₃/SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo‐induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure.     

Designable Luminescence with Quantum Dot–Silver Plasmon Coupler

We explore a strongly interacting QDs/Ag plasmonic coupling structure that enables multiple approaches to manipulate light emission from QDs. Group II–VI semiconductor QDs with unique surface states (SSs) impressively modify the plasmonic character of the contiguous Ag nanostructures whereby the localized plasmons (LPs) in the Ag nanostructures can effectively extract the non‐radiative SSs of the QDs to radiatively emit via SS–LP resonance. The SS–LP coupling is demonstrated to be readily tunable through surface‐state engineering both during QD synthesis and in the post‐synthesis stage. The combination of surface‐state engineering and band‐tailoring engineering allows us to precisely control the luminescence color of the QDs and enables the realization of white‐light emission with single‐size QDs. Being a versatile metal, the Ag in our optical device functions in multiple ways: as a support for the LPs, for optical reflection, and for electrical conduction. Two application examples of the QDs/Ag plasmon coupler for optical devices are given, an Ag microcavity + plasmon‐coupling structure and a new QD light‐emitting diode. The new QDs/Ag plasmon coupler opens exciting possibilities in developing novel light sources and biomarker detectors.     

High‐Performance Inorganic Perovskite Quantum Dot–Organic Semiconductor Hybrid Phototransistors

All‐inorganic lead halide perovskite quantum dots (IHP QDs) have great potentials in photodetectors. However, the photoresponsivity is limited by the low charge transport efficiency of the IHP QD layers. High‐performance phototransistors based on IHP QDs hybridized with organic semiconductors (OSCs) are developed. The smooth surface of IHP QD layers ensures ordered packing of the OSC molecules above them. The OSCs significantly improve the transportation of the photoexcited charges, and the gate effect of the transistor structure significantly enhances the photoresponsivity while simultaneously maintaining high I _photo/I _dark ratio. The devices exhibit outstanding optoelectronic properties in terms of photoresponsivity (1.7 × 10⁴ A W^?1), detectivity (2.0 × 10¹⁴ Jones), external quantum efficiency (67000%), I _photo/I _dark ratio (8.1 × 10⁴), and stability (100 d in air). The overall performances of our devices are superior to state‐of‐the‐art IHP photodetectors. The strategy utilized here is general and can be easily applied to many other perovskite photodetectors.     

Electroluminescence from a mixed red-green-blue colloidal quantum dot monolayer

We demonstrate light emitting devices (LEDs) with a broad spectral emission generated by electroluminescence from a mixed-monolayer of red, green, and blue emitting colloidal quantum dots (QDs) in a hybrid organic/inorganic structure. The colloidal QDs are reproducibly synthesized and yield high luminescence efficiency materials suitable for LED applications. Independent processing of the organic charge transport layers and the QD luminescent layer allows for precise tuning of the emission spectrum without changing the device structure, simply by changing the ratio of different color QDs in the active layer. Spectral tuning is demonstrated through fabrication of white QD-LEDs that exhibit external quantum efficiencies of 0.36% (Commission Internationale de l'Eclairage) coordinates of (0.35, 0.41) at video brightness, and color rendering index of 86 as compared to a 5500 K blackbody reference.     

Epitaxial Growth of CsPbX3 (X = Cl,Br, I) Perovskite Quantum Dots via Surface Chemical Conversion of Cs2GeF6 Double Perovskites: A Novel Strategy for the Formation of Leadless Hybrid Perovskite Phosphors with Enhanced Stability

Lead halide perovskites (LHPs) have received increased attention owing to their intriguing optoelectronic and photonic properties. However, the toxicity of lead and the lack of long‐term stability are potential obstacles for the application of LHPs. Herein, the epitaxial synthesis of CsPbX₃ (X = Cl, Br, I) perovskite quantum dots (QDs) by surface chemical conversion of Cs₂GeF₆ double perovskites with PbX₂ (X = Cl, Br, I) is reported. The experimental results show that the surface of the Cs₂GeF₆ double perovskites is partially converted into CsPbX₃ perovskite QDs and forms a CsPbX₃/Cs₂GeF₆ hybrid structure. The theoretical calculations reveal that the CsPbBr₃ conversion proceeds at the Cs₂GeF₆ edge through sequential growth of multiple PbBr₆ ^4? layers. Through the conversion strategy, luminescent and color‐tunable CsPbX₃ QDs can be obtained, and these products present high stability against decomposition due to anchoring effects. Moreover, by partially converting red emissive Cs₂GeF₆:Mn⁴⁺ to green emissive CsPbBr₃, the CsPbBr₃/Cs₂GeF₆:Mn⁴⁺ hybrid can be employed as a low‐lead hybrid perovskite phosphor on blue LED chips to produce white light. The leadless CsPbX₃/Cs₂GeF₆ hybrid structure with stable photoluminescence opens new paths for the rational design of efficient emission phosphors and may stimulate the design of other functional CsPbX₃/Cs‐containing hybrid structures.     

Hybrid PbS Quantum‐Dot‐in‐Perovskite for High‐Efficiency Perovskite Solar Cell

In this study, a facile and effective approach to synthesize high‐quality perovskite‐quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH₃NH₃PbI₃ (MAPbI₃) precursor to form a QD‐in‐perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X‐ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI₃‐PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.     

Extremely Vivid,Highly Transparent,and Ultrathin Quantum Dot Light‐Emitting Diodes

Displaying information on transparent screens offers new opportunities in next‐generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such “see‐through” displays to show vivid images over clear background view. Here transparent quantum dot light‐emitting diodes (Tr‐QLEDs) are reported with high brightness (bottom: ≈43 000 cd m^?2, top: ≈30 000 cd m^?2, total: ≈73 000 cd m^?2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr‐QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr‐QLEDs (513 pixels in.^?1) shows the potential of the full‐color transparent display.     

Stretchable Organometal‐Halide‐Perovskite Quantum‐Dot Light‐Emitting Diodes

Stretchable light‐emitting diodes (LEDs) and electroluminescent capacitors have been reported to potentially bring new opportunities to wearable electronics; however, these devices lack in efficiency and/or stretchability. Here, a stretchable organometal‐halide‐perovskite quantum‐dot LED with both high efficiency and mechanical compliancy is demonstrated. The hybrid device employs an ultrathin (<3 µm) LED structure conformed on a surface‐wrinkled elastomer substrate. Its luminescent efficiency is up to 9.2 cd A^?1, which is 70% higher than a control diode fabricated on the rigid indium tin oxide/glass substrate. Mechanical deformations up to 50% tensile strain do not induce significant loss of the electroluminescent property. The device can survive 1000 stretch–release cycles of 20% tensile strain with small fluctuations in electroluminescent performance.     

White light emitting diodes realized by using an active packaging method with CdSe/ZnS quantum dots dispersed in photosensitive epoxy resins

White light emitting diodes (LEDs) have been realized using the active packaging (AP) method. The starting materials were bare InGaN LED chips and CdSe/ZnS core-shell quantum dots (QDs) dispersed in photosensitive epoxy resins. Such hybrid LED devices were fabricated using QD mixtures with one ('single'), two ('dual') or four ('multi') emission wavelengths. The?AP method allows for convenient adjustment of multiple parameters such as the CIE-1931 coordinate (x, y), color temperature, and color rending index (CRI). All samples show good white balance, and under a 20?mA working current the luminous efficacies of the single, dual, and multi hybrid devices were 8.1?lm?W(-1), 5.1?lm?W(-1), and 6.4?lm?W(-1), respectively. The corresponding quantum efficiencies were 4.1%, 3.1%, and 3.1%; the CRIs were 21.46, 43.76, and 66.20; and the color temperatures were 12?000, 8190, and 7740?K. This shows that the CRI of the samples can be enhanced by broadening the QD emission band, as is exemplified by the 21.46 CRI of the single hybrid LED compared to the 66.20 value for the multi hybrid LED. In addition, we were able to increase the CRI of the single hybrid LED from 15.31 to 32.50 by increasing the working currents from 1 to 50?mA.     

Rare‐Earth‐Element‐Ytterbium‐Substituted Lead‐Free Inorganic Perovskite Nanocrystals for Optoelectronic Applications

Lead‐(Pb‐) halide perovskite nanocrystals (NCs) are interesting nanomaterials due to their excellent optical properties, such as narrow‐band emission, high photoluminescence (PL) efficiency, and wide color gamut. However, these NCs have several critical problems, such as the high toxicity of Pb, its tendency to accumulate in the human body, and phase instability. Although Pb‐free metal (Bi, Sn, etc.) halide perovskite NCs have recently been reported as possible alternatives, they exhibit poor optical and electrical properties as well as abundant intrinsic defect sites. For the first time, the synthesis and optical characterization of cesium ytterbium triiodide (CsYbI₃) cubic perovskite NCs with highly uniform size distribution and high crystallinity using a simple hot‐injection method are reported. Strong excitation‐independent emission and high quantum yields for the prepared NCs are verified using photoluminescence measurements. Furthermore, these CsYbI₃ NCs exhibit potential for use in organic–inorganic hybrid photodetectors as a photoactive layer. The as‐prepared samples exhibit clear on–off switching behavior as well as high photoresponsivity (2.4 × 10³ A W^?1) and external quantum efficiency (EQE, 5.8 × 10⁵%) due to effective exciton dissociation and charge transport. These results suggest that CsYbI₃ NCs offer tremendous opportunities in electronic and optoelectronic applications, such as chemical sensors, light emitting diodes (LEDs), and energy conversion and storage devices.