Proton‑Prompted Ligand Exchange to Achieve High‑Efficiency CsPbI_(3) Quantum Dot Light‑Emitting Diodes

CsPbI_(3)perovskite quantum dots(QDs)are ideal materials for the next generation of red light-emitting diodes.However,the low phase stability of CsPbI_(3)QDs and long-chain insulating capping ligands hinder the improvement of device performance.Traditional in-situ ligand replacement and ligand exchange after synthesis were often difficult to control.Here,we proposed a new ligand exchange strategy using a proton-prompted insitu exchange of short 5-aminopentanoic acid ligands with long-chain oleic acid and oleylamine ligands to obtain stable small-size CsPbI_(3)QDs.This exchange strategy maintained the size and morphology of CsPbI_(3)QDs and improved the optical properties and the conductivity of CsPbI_(3)QDs films.As a result,high-efficiency red QD-based light-emitting diodes with an emission wavelength of 645 nm demonstrated a record maximum external quantum efficiency of 24.45%and an operational half-life of 10.79 h.

Efficient PbS quantum dots tandem solar cells through compatible interconnection layer

Lead sulfide quantum dots(PbS QDs) hold unique characteristics, including bandgap tunability, solutionprocessability etc., which make them highly applicable in tandem solar cells(TSCs). In all QD TSCs, its efficiency lags much behind to their single junction counterparts due to the deficient interconnection layer(ICL) and defective subcells. To improve TSCs performance, we developed three kinds of ICL structures based on 1.34 and 0.96 e V PbS QDs subcells. The control, 1,2-ethanedithiol capped PbS QDs(PbS-EDT)/Au/tin dioxide(SnO_(2))/zinc oxide(Zn O), utilized SnO_(2) layer to obtain high surface compactness.However, its energy level mismatch causes incomplete recombination. Bypassing it, the second ICL(PbS-EDT/Au/Zn O) removed SnO_(2) and boosted the power conversion efficiency(PCE) from 5.75% to 8.69%. In the third ICL(PbS-EDT/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine](PTAA)/Au/Zn O), a thin layer of PTAA can effectively fill fissures on the surface of PbS-EDT and also protect the front cells from solvent penetration. This TSC obtained a PCE of 9.49% with an open circuit voltage of 0.91 V, a short circuit current density of 15.47 m A/cm~2, and a fill factor of 67.7%. To the best of our knowledge, this was the highest PCE achieved by all PbS QD TSCs reported to date. These TSCs maintained stable performance for a long working time under ambient conditions.

Advantageous properties of halide perovskite quantum dots towards energy-efficient sustainable applications

As lead halide perovskite(LHP)semiconductors have shown tremendous promise in many application fields,and particularly made strong impact in the solar photovoltaic area,low dimensional quantum dot forms of these perovskites are showing the potential to make distinct marks in the fields of electronics,optoelectronics and photonics.The so-called perovskite quantum dots(PQDs)not only possess the most important features of LHP materials,i.e.,the unusual high defect tolerance,but also demonstrate clear quantum size effects,along with exhibiting desirable optoelectronic properties such as near perfect photoluminescent quantum yield,multiple exciton generation and slow hot-carrier cooling.Here,we review the advantageous properties of these nanoscale perovskites and survey the prospects for diverse applications which include lightemitting devices,solar cells,photocatalysts,lasers,detectors and memristors,emphasizing the distinct superiorities as well as the challenges.

High-Performance Perovskite Solar Cells with Zwitterion-Capped-ZnO Quantum Dots as Electron Transport Layer and NH_(4)X(X=F,Cl,Br)Assisted Interfacial Engineering

The systematic advances in the power conversion efficiency(PCE)and stability of perovskite solar cells(PSCs)have been driven by the developments of perovskite materials,electron transport layer(ETL)materials,and interfacial passivation between the relevant layers.While zinc oxide(ZnO)is a promising ETL in thin film photovoltaics,it is still highly desirable to develop novel synthetic methods that allow both fine-tuning the versatility of ZnO nanomaterials and improving the ZnO/perovskite interface.Among various inorganic and organic additives,zwitterions have been effectively utilized to passivate the perovskite films.In this vein,we develop novel,well-characterized betaine-coated ZnO QDs and use them as an ETL in the planar n-i-p PSC architecture,combining the ZnO QDs-based ETL with the ZnO/perovskite interface passivation by a series of ammonium halides(NH_(4)X,where X=F,Cl,Br).The champion device with the NH4F passivation achieves one of the highest performances reported for ZnO-based PSCs,exhibiting a maximum PCE of~22%with a high fill factor of 80.3%and competitive stability,retaining~78%of its initial PCE under 1 Sun illumination with maximum power tracking for 250 h.

Coupling of BiOCl Ultrathin Nanosheets with Carbon Quantum Dots for Enhanced Photocatalytic Performance

Over the past few decades,photocatalysis technology has received extensive attention because of its potential to mitigate or solve energy and environmental pollution problems.Designing novel materials with outstanding photocatalytic activities has become a research hotspot in this field.In this study,we prepared a series of photocatalysts in which BiOCl nanosheets were modified with carbon quantum dots(CQDs)to form CQDs/BiOCl composites by using a simple solvothermal method.The photocatalytic performance of the resulting CQDs/BiOCl composite photocatalysts was assessed by rhodamine B and tetracycline degradation under visible-light irradiation.Compared with bare BiOCl,the photocatalytic activity of the CQDs/BiOCl composites was significantly enhanced,and the 5 wt%CQDs/BiOCl composite exhibited the highest photocatalytic activity with a degradation efficiency of 94.5%after 30 min of irradiation.Moreover,photocatalytic N_(2)reduction performance was significantly improved after introducing CQDs.The 5 wt%CQDs/BiOCl composite displayed the highest photocatalytic N_(2)reduction performance to yield NH_3(346.25μmol/(g h)),which is significantly higher than those of 3 wt%CQDs/BiOCl(256.04μmol/(g h)),7 wt%CQDs/BiOCl(254.07μmol/(g h)),and bare BiOCl(240.19μmol/(g h)).Our systematic characterizations revealed that the key role of CQDs in improving photocatalytic performance is due to their increased light harvesting capacity,remarkable electron transfer ability,and higher photocatalytic activity sites.

Effective Activation of Melamine for Synchronous Synthesis of Catalytically Active Nanosheets and Fluorescence-Responsive Quantum Dots

Because of the low reactivity of cyclic nitrides,liquid-phase synthesis of carbon nitride introduces challenges despite its favorable potential for energy-efficient preparation and superior applications.In this study,we demonstrate a strong interaction between citric acid and melamine through experimental observation and theoretical simulation,which eff ectively activates melamine-condensation activity and produces carbon-rich carbon nitride nanosheets(CCN NSs)during hydrothermal reaction.Under a large specific surface area and increased light absorption,these CCN NSs demonstrate significantly enhanced photocatalytic activity in CO_(2) reduction,increasing the CO production rate by approximately tenfold compared with hexagonal melamine(h-Me).Moreover,the product selectivity of CCN NSs reaches up to 93.5%to generate CO from CO_(2).Furthermore,the annealed CCN NSs exhibit a CO conversion rate of up to 95.30μmol/(g h),which indicates an 18-fold increase compared with traditional carbon nitride.During the CCN NS synthesis,nitrogen-doped carbon quantum dots(NDC QDs)are simultaneously produced and remain suspended in the supernatant after centrifugation.These QDs disperse well in water and exhibit excellent luminescent properties(QY=67.2%),allowing their application in the design of selective and sensitive sensors to detect pollutants such as pesticide 2,4-dichlorophenol with a detection limit of as low as 0.04μmol/L.Notably,the simultaneous synthesis of CCN NSs and NDC QDs provides a cost-eff ective and highly efficient process,yielding products with superior capabilities for catalytic conversion of CO_(2) and pollutant detection,respectively.

The exchange interaction between neighboring quantum dots:physics and applications in quantum information processing

Electron spins confined in semiconductor quantum dots(QDs)are one of potential candidates for physical implementation of scalable quantum information processing technologies.Tunnel coupling based inter exchange interaction between QDs is crucial in achieving single-qubit manipulation,two-qubit gate,quantum communication and quantum simulation.This review first provides a theoretical perspective that surveys a general framework,including the Helter−London approach,the Hund−Mulliken approach,and the Hubbard model,to describe the inter exchange interactions between semiconductor quantum dots.An electrical method to control the inter exchange interaction in a realistic device is proposed as well.Then the significant achievements of inter exchange interaction in manipulating single qubits,achieving two-qubit gates,performing quantum communication and quantum simulation are reviewed.The last part is a summary of this review.

Paving continuous heat dissipation pathways for quantum dots in polymer with orangeinspired radially aligned UHMWPE fibers

Thermal management of nanoscale quantum dots(QDs)in light-emitting devices is a long-lasting challenge.The existing heat transfer reinforcement solutions for QDs-polymer composite mainly rely on thermal-conductive fillers.However,this strategy failed to deliver the QDs’heat generation across a long distance,and the accumulated heat still causes considerable temperature rise of QDs-polymer composite,which eventually menaces the performance and reliability of lightemitting devices.Inspired by the radially aligned fruit fibers in oranges,we proposed to eliminate this heat dissipation challenge by establishing long-range ordered heat transfer pathways within the QDs-polymer composite.Ultrahigh molecular weight polyethylene fibers(UPEF)were radially aligned throughout the polymer matrix,thus facilitating massive efficient heat dissipation of the QDs.Under a UPEF filling fraction of 24.46 vol%,the in-plane thermal conductivity of QDs-radially aligned UPEF composite(QDs-RAPE)could reach 10.45 W m^(−1) K^(−1),which is the highest value of QDs-polymer composite reported so far.As a proof of concept,the QDs’working temperature can be reduced by 342.5℃ when illuminated by a highly concentrated laser diode(LD)under driving current of 1000 mA,thus improving their optical performance.This work may pave a new way for next generation high-power QDs lighting applications.

Majorana tunneling in a one-dimensional wire with non-Hermitian double quantum dots

The combination of non-Hermitian physics and Majorana fermions can give rise to new effects in quantum transport systems. In this work, we investigate the interplay of PT-symmetric complex potentials, Majorana tunneling and interdot tunneling in a non-Hermitian double quantum dots system. It is found that in the weak-coupling regime the Majorana tunneling has pronounced effects on the transport properties of such a system, manifested as splitting of the single peak into three and a reduced 1/4 peak in the transmission function. In the presence of the PT-symmetric complex potentials and interdot tunneling, the 1/4 central peak is robust against them, while the two side peaks are tuned by them. The interdot tunneling only induces asymmetry, instead of moving the conductance peak, due to the robustness of the Majorana modes. There is an exceptional point induced by the union of Majorana tunneling and interdot tunneling. With increased PT-symmetric complex potentials, the two side peaks will move towards each other. When the exceptional point is passed through, these two side peaks will disappear. In the strong-coupling regime, the Majorana fermion induces a 1/4 conductance dip instead of the three-peak structure. PT-symmetric complex potentials induce two conductance dips pinned at the exceptional point. These effects should be accessible in experiments.

Small but mighty:Empowering sodium/potassium-ion battery performance with S-doped SnO_(2) quantum dots embedded in N,S codoped carbon fiber network

SnO_(2) has been extensively investigated as an anode material for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)due to its high Na/K storage capacity,high abundance,and low toxicity.However,the sluggish reaction kinetics,low electronic conductivity,and large volume changes during charge and discharge hinder the practical applications of SnO_(2)-based electrodes for SIBs and PIBs.Engineering rational structures with fast charge/ion transfer and robust stability is important to overcoming these challenges.Herein,S-doped SnO_(2)(S-SnO_(2))quantum dots(QDs)(≈3 nm)encapsulated in an N,S codoped carbon fiber networks(S-SnO_(2)-CFN)are rationally fabricated using a sequential freeze-drying,calcination,and S-doping strategy.Experimental analysis and density functional theory calculations reveal that the integration of S-SnO_(2) QDs with N,S codoped carbon fiber network remarkably decreases the adsorption energies of Na/K atoms in the interlayer of SnO_(2)-CFN,and the S doping can increase the conductivity of SnO_(2),thereby enhancing the ion transfer kinetics.The synergistic interaction between S-SnO_(2) QDs and N,S codoped carbon fiber network results in a composite with fast Na+/K+storage and extraordinary long-term cyclability.Specifically,the S-SnO_(2)-CFN delivers high rate capacities of 141.0 mAh g^(−1) at 20 A g^(−1) in SIBs and 102.8 mAh g^(−1) at 10 A g^(−1) in PIBs.Impressively,it delivers ultra-stable sodium storage up to 10,000 cycles at 5 A g^(−1) and potassium storage up to 5000 cycles at 2 A g^(−1).This study provides insights into constructing metal oxide-based carbon fiber network structures for high-performance electrochemical energy storage and conversion devices.

Finely regulated luminescent Ag-In-Ga-S quantum dots with green-red dual emission toward white light-emitting diodes

Ag-In-Ga-S(AIGS)quantum dots(QDs)have recently attracted great interests due to the outstanding optical properties and eco-friendly components,which are considered as an alternative replacement for toxic Pb-and Cd-based QDs.However,enormous attention has been paid to how to narrow their broadband spectra,ignoring the application advantages of the broadband emission.In this work,the AIGS QDs with controllable broad green-red dual-emission are first reported,which is achieved through adjusting the size distribution of QDs by controlling the nucleation and growth of AIGS crystals.Resultantly,the AIGS QDs exhibit broad dual-emission at green-and red-band evidenced by photoluminescence(PL)spectra,and the PL relative intensity and peak position can be finely adjusted.Furthermore,the dual-emission is the intrinsic characteristics from the difference in confinement effect of large particles and tiny particles confirmed by temperature-dependent PL spectra.Accordingly,the AIGS QDs(the size consists of 17 nm and 3.7 nm)with 530 nm and 630 nm emission could successfully be synthesized at 220°C.By combining the blue light-emitting diode(LED)chips and dual-emission AIGS QDs,the constructed white light-emitting devices(WLEDs)exhibit a continuous and broad spectrum like natural sunlight with the Commission Internationale de l’Eclairage(CIE)chromaticity coordinates of(0.33,0.31),a correlated color temperature(CCT)of 5425 K,color rendering index(CRI)of 90,and luminous efficacy of radiation(LER)of 129 lm/W,which indicates that the AIGS QDs have huge potential for lighting applications.

Embedded high-quality ternary GaAs_(1−x)Sb_(x) quantum dots in GaAs nanowires by molecular-beam epitaxy

Semiconductor quantum dots are promising candidates for preparing high-performance single photon sources.A basic requirement for this application is realizing the controlled growth of high-quality semiconductor quantum dots.Here,we report the growth of embedded GaAs_(1−x)Sb_(x) quantum dots in GaAs nanowires by molecular-beam epitaxy.It is found that the size of the GaAs_(1−x)Sb_(x) quantum dot can be well-defined by the GaAs nanowire.Energy dispersive spectroscopy analyses show that the antimony content x can be up to 0.36 by tuning the growth temperature.All GaAs_(1−x)Sb_(x) quantum dots exhibit a pure zinc-blende phase.In addition,we have developed a new technology to grow GaAs passivation layers on the sidewalls of the GaAs_(1−x)Sb_(x) quantum dots.Different from the traditional growth process of the passivation layer,GaAs passivation layers can be grown simultaneously with the growth of the embedded GaAs_(1−x)Sb_(x) quantum dots.The spontaneous GaAs passivation layer shows a pure zinc-blende phase due to the strict epitaxial relationship between the quantum dot and the passivation layer.The successful fabrication of embedded high-quality GaAs_(1−x)Sb_(x) quantum dots lays the foundation for the realization of GaAs_(1−x)Sb_(x)-based single photon sources.

Threshold-independent method for single-shot readout of spin qubits in semiconductor quantum dots

The single-shot readout data process is essential for the realization of high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor quantum dots. However, the fidelity and visibility of the readout process are sensitive to the choice of the thresholds and limited by the experimental hardware. By demonstrating the linear dependence between the measured spin state probabilities and readout visibilities along with dark counts, we describe an alternative threshold-independent method for the single-shot readout of spin qubits in semiconductor quantum dots. We can obtain the extrapolated spin state probabilities of the prepared probabilities of the excited spin state through the threshold-independent method. We then analyze the corresponding errors of the method, finding that errors of the extrapolated probabilities cannot be neglected with no constraints on the readout time and threshold voltage. Therefore, by limiting the readout time and threshold voltage, we ensure the accuracy of the extrapolated probability. We then prove that the efficiency and robustness of this method are 60 times larger than those of the most commonly used method. Moreover, we discuss the influence of the electron temperature on the effective area with a fixed external magnetic field and provide a preliminary demonstration for a single-shot readout of up to 0.7K/1.5T in the future.

A highly sensitive ratiometric near-infrared nanosensor based on erbium-hyperdoped silicon quantum dots for iron(Ⅲ) detection

Ratiometric fluorescent detection of iron(Ⅲ)(Fe^(3+))offers inherent self-calibration and contactless analytic capabilities.However,realizing a dual-emission near-infrared(NIR)nanosensor with a low limit of detection(LOD)is rather challenging.In this work,we report the synthesis of water-dispersible erbium-hyperdoped silicon quantum dots(Si QDs:Er),which emit NIR light at the wavelengths of 810 and 1540 nm.A dual-emission NIR nanosensor based on water-dispersible Si QDs:Er enables ratiometric Fe^(3+)detection with a very low LOD(0.06μM).The effects of pH,recyclability,and the interplay between static and dynamic quenching mechanisms for Fe^(3+)detection have been systematically studied.In addition,we demonstrate that the nanosensor may be used to construct a sequential logic circuit with memory functions.

Manipulation of internal blockage in triangular triple quantum dot

We utilize the calculation of hierarchical equations of motion to demonstrate that the spin-dependent properties between adjacent quantum dots(QDs)can be changed by breaking the internal symmetry configuration,corresponding to the inversion of dominant chiral states.In the linear triple quantum dots(LTQDs)connected to two electron reservoirs,we can observe that the blockage appears at the triangle triple quantum dots(TTQDs)by gradually increasing the coupling strength between next-nearest double QDs.When the initial coupling between LTQDs has altered,the internal chiral circulation also undergoes the corresponding transform,thus achieving qualitative regulation and detection of the blocking region.We also investigate the response of the chiral circulation to the dot–lead coupling strength,indicating the overall robust chiral circulation of the TTQDs frustration.

Unraveling the efficiency losses and improving methods in quantum dot-based infrared up-conversion photodetectors

Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,the huge efficiency losses caused by integrating the PD and QLED together hasn’t been studied sufficiently.This work revealed at least three origins for the efficiency losses.First,the PD unit and QLED unit usually didn’t work under optimal conditions at the same time.Second,the potential barriers and traps at the interconnection between PD and QLED units induced unfavorable carrier recombination.Third,much emitted visible light was lost due to the strong visible absorption in the PD unit.Based on the understandings on the loss mechanisms,the infrared up-conversion photodetectors were optimized and achieved a breakthrough photon-to-photon conversion efficiency of 6.9%.This study provided valuable guidance on how to optimize the way of integration for up-conversion photodetectors.

A Polaron in a Quantum Dot quantum Well

The polaron effect in a quantum dot quantum well (QDQW)system is investigated by using the perturbation method. Both the bound electron states outside and inside the shell well are taken into account . Numerical calculation on the CdS/HgS QDQW shows that the phonon correction to the electron ground state energy is quite significant and cannot be neglected.

Bound polarons in quantum dot quantum well structures

The problem of bound polarons in quantum dot quantum well （QDQW） structures is studied theoretically. The eigenfrequencies of bulk longitudinal optical （LO） and surface optical （SO） modes are derived in the framework of the dielectric continuum approximation. The electron-phonon interaction Hamiltonian for QDQW structures is obtained and the exchange interaction between impurity and LO-phonons is discussed. The binding energy and the trapping energy of the bound polaron in CdS/HgS QDQW structures are calculated. The numerical results reveal that there exist three branches of eigenfrequencies of surface optical vibration in the CdS/HgS QDQW structure. It is also shown that the binding energy and the trapping energy increase as the inner radius of the QDQW structure decreases, with the outer radius fixed, and the trapping energy takes a major part of the binding energy when the inner radius is very small.

Quantum Coupling Effect between Quantum Dot and Quantum Well in a Resonant Tunneling Photon-Number-Resolving Detector

Excited states of lnAs quantum dots （QDs） can be energetically coupled with the confined level of OaAs quantum wells （QWs） in a thin-barrier resonant tunneling diode （RTD）. Single charge variation in the coupled QD can effectively switch on/off the resonant tunneling current passing through RTD, not only for emcient single-photon detection but also for photon-number-resolving detection. We present the study of the Q,D-QW coupling effect in the quantum dot coupled resonant tunneling diode （QD-cRTD） and figure out important factors for further improving the detector performance.

One-pot facile synthesis of highly photoluminescent graphene quantum dots with oxygen-rich groups

To achieve a new type of carbon-based quantum dots with unique photoluminescence PL a simple approach for fabrication of graphene quantum dots GQDs with oxygen-rich groups was developed via the hydrothermal reaction by using graphene oxides GOs as a precursor. Transmission electron microscope TEM and atomic force microscope AFM characterizations confirmed that the sizes and heights of GQDs were 5.02±0.92 nm and 0.6 nm respectively.A strong PL emission exhibited unique excitation wavelength dependent features.Also the carbene-like free zigzag edge sites were proposed to be the origin of the strong PL emission.The GQDs were demonstrated to be a superior probe for Fe3＋ detection in aqueous solution with a high sensitivity and feasibility due to the special coordinate interaction between Fe3＋and the phenolic hydroxyl group at GQDs.