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OBJECTIVES To evaluate clinico-radiologic markers that predict poor overall survival (OS) in sporadic Creutzfeldt-Jakob disease (sCJD) and to develop a prognostic model. MATERIALS AND METHODS Patients with newly diagnosed sCJD were included who underwent diffusion-weighted imaging (DWI) from February 2000 to July 2020. The impact of 9 clinico-radiologic features on OS was analyzed using univariable and multivariable Cox proportional hazards regression model. The DWI prognostic score model was generated. The weighted kappa was calculated for interobserver agreement. RESULTS Sixty patients (mean age ± SD, 61.0 ± 9.7 years, 32 women) were included. Univariable analysis showed positive associations between poor OS and patient age (p = 0.003), extent of involved cortical lobes (p = 0.11), involvement of caudate nucleus (p = 0.07), and putamen (p = 0.04). Multivariable analysis demonstrated two independent prognostic factors: age ≥ 60 (HR 2.65, 95% CI, 1.41-4.98), and diffusion restriction in caudate nucleus and putamen (HR 2.24, 95% CI, 1.15-4.37). Based on these features, the DWI prognostic score model was generated: low-risk (0-1 point), intermediate-risk (2-3 points), and high-risk (4-5 points) groups. Median OS in high-risk group was 1.7 months, which was significantly shorter than those in the intermediate-risk (14.2 months) and low-risk (26.5 months) groups (p < 0.001). Interobserver agreements were excellent (κ = 0.91-0.92). CONCLUSIONS Our study demonstrated that age and diffusion restriction in caudate nucleus and putamen were the independent prognostic factors of poor overall survival in sporadic Creutzfeldt-Jakob disease. Our DWI prognostic score model may be useful in clinical settings for disease stratification. KEY POINTS • Age ≥ 60, and diffusion restriction in caudate nucleus and putamen were the independent prognostic factors of poor overall survival in sCJD. • Based on our DWI prognostic score model, median overall survival in high-risk group was 1.7 months, which was significantly shorter than those in the intermediate-risk group (14.2 months) and low-risk group (26.5 months) (p < 0.001). • The proposed DWI prognostic score model may be useful in clinical settings for disease stratification.

A graphene-PbS quantum dot (QD) composite for application in high-performance near-infrared (NIR) photodetectors (PDs) is proposed in this study. A single-layer graphene flake and oleic acid-capped PbS QD composite is fabricated through the conventional sonication process, in hexane solution. Field emission scanning electron microscopy images of the graphene-PbS QD composite dispersed on a glass substrate confirm that the composite contains both aggregated graphene flakes and single-layer graphene with wrinkles; Transmission electron microscopy images reveal close packing with uniform size. The increased absorbance and quenched photoluminescence intensity of the graphene-PbS QD composite supports enhanced photoinduced charge transfer between graphene and the PbS QDs. Moreover, the specific Raman mode of the PbS QDs, embedded in the spectrum, is enhanced by combination with graphene, which can be interpreted by SERS as relevant to the photoinduced charge transfer between the Pbs QDs and graphene. For device application, a PD structure comprised by graphene-PbS QDs is fabricated. The photocurrent of the PD is measured using a conventional probe station with a 980-nm NIR laser diode. In the fabricated PD comprising graphene-PbS QDs, five-times higher photocurrent, 22% faster rise time, and 47% faster decay time are observed, compared to that comprising PbS QDs alone. This establishes the potential of the graphene-PbS QD composite for application in ultrathin, flexible, high-performance NIR PDs.

The fine control over the surface of lead sulfide colloidal quantum dots (PbS CQDs) is increasingly important to achieve enhanced device performance. In particular, the in-gap trap state resulting from the surface hydroxylation of PbS CQDs is considered detrimental to photovoltaic performance. In this study, we developed a method to avoid hydroxyl formation on the PbS CQD surface by using an in situ solution-phase ligand-exchange process. The complete elimination of protic solvents and other hydroxyl sources from the CQD synthesis to device fabrication produced PbS CQD films without undesired hydroxyl ligands with a reduced trap density. In this process, the purification process, which accounts for nearly 60% of the synthesis cost, is completely excluded. The presence of trap states verified through optical analysis and the hydroxylation observed via surface analysis clearly agreed with the device characterization obtained by transient photovoltage and photocurrent. Consequently, the open-circuit voltage of the PbS CQD solar cells is improved by up to 10%, yielding a certified power-conversion efficiency of 11.6%.

Solution-processed semiconductors are promising materials to realize optoelectronic devices that combine high performance with inexpensive manufacturing. In particular, the exploitation of colloidal quantum dots (CQDs) capable of harvesting infrared photons, in conjunction with visible-absorbing organic chromophores, has been demonstrated as an interesting route. Unfortunately, CQD/organic hybrid photovoltaics have been limited to power conversion efficiencies (PCEs) below 10% due to chemical mismatch and difficulties in facilitating charge collection. Here we devise a hybrid architecture that overcomes these limitations by introducing small molecules into the CQD/organic stacked structure. The small molecule complements CQD absorption and creates an exciton cascade with the host polymer, thus enabling efficient energy transfer and also promoting exciton dissociation at heterointerfaces. The resulting hybrid solar cells exhibit PCEs of 13.1% and retain over 80% of their initial PCE after 150 h of continuous operation unencapsulated, outperforming present air-processed solution-cast CQD/organic photovoltaics. Colloidal quantum dots and organics have complementary properties apt for photovoltaics, yet their combination has led to poor charge collection. Here, Baek et al. introduce small molecules that act as a bridge between quantum dots and polymers, thus improving device efficiency and stability.

Colloidal quantum dots (QDs) are nanosized semiconductors whose electronic features are dictated by the quantum confinement effect. The optical, electrical, and chemical properties of QDs are influenced by their dimensions and surface landscape. The surface of II–VI and IV–VI QDs has been extensively explored; however, in-depth investigations on the surface of III–V QDs are still lagging behind. This Perspective discusses the current understanding of the surface of III–V QDs, outlines deep trap states presented by surface defects, and suggests strategies to overcome challenges associated with deep traps. Lastly, we discuss a route to create well-defined facets in III–V QDs by providing a platform for surface studies and a recently reported approach in atomistic understanding of covalent III–V QD surfaces using the electron counting model with fractional dangling bonds., Unveiling the atomistic surface structure of colloidal quantum dots may provide the route to rational design of highly performing III–V nanocrystals with control over energy levels position, surface energy, trap passivation, and heterojunction interface.

Strain engineering of perovskite quantum dots (pQDs) enables widely tunable photonic device applications. However, manipulation at the single-emitter level has never been attempted. Here, we present a tip-induced control approach combined with tip-enhanced photoluminescence (TEPL) spectroscopy to engineer strain, bandgap, and the emission quantum yield of a single pQD. Single CsPbBrxI3-x pQDs are clearly resolved through hyperspectral TEPL imaging with ∼10 nm spatial resolution. The plasmonic tip then directly applies pressure to a single pQD to facilitate a bandgap shift up to ∼62 meV with Purcell-enhanced PL increase as high as ∼105 for the strain-induced pQD. Furthermore, by systematically modulating the tip-induced compressive strain of a single pQD, we achieve dynamical bandgap engineering in a reversible manner. In addition, we facilitate the quantum dot coupling for a pQD ensemble with ∼0.8 GPa tip pressure at the nanoscale estimated theoretically. Our approach presents a strategy to tune the nano-opto-electro-mechanical properties of pQDs at the single-crystal level.

We introduce indium arsenide colloidal quantum dot films for photovoltaic devices, fabricated by two-step surface modification. Native ligands and unwanted oxides on the surface are peeled off followed by passivating with incoming atomic or short ligands. The near-infrared-absorbing n-type indium arsenide colloidal quantum dot films can be tuned in energy-level positions up to 0.4 eV depending on the surface chemistry, and consequently, they boost collection efficiency when used in various emerging solar cells. As an example, we demonstrate p–n junction between n-type indium arsenide and p-type lead sulfide colloidal quantum dot layers, which leads to a favorable electronic band alignment and charge extraction from both colloidal quantum dot layers. A certified power conversion efficiency of 7.92% is achieved without additionally supporting carrier transport layers. This study provides richer materials to explore for high-efficiency emerging photovoltaics and will broaden research interest for various optoelectronic applications using the n-type covalent nanocrystal arrays., Existing n-type colloidal quantum dot materials easily lose their doping polarity in air. Here Song et al. passivate the reactive covalent surface of indium arsenide quantum dots to gain the energy-level tunability and show p–n junction type solar cells with 7.92% certified efficiency.

Power conversion efficiencies of colloidal quantum dot solar cells, which have focused mainly on lead chalcogenide systems until recently, have increased rapidly and currently exceed 12%. Among the many issues involved in commercialization of this technology as a consumer product, lead-based materials in these systems must be replaced. This requires the use of a low-cost, low-loss, and non-toxic chemical, along with the development of an eco-friendly manufacturing process. Herein, we review recent progress in ecofriendly colloidal quantum dot photovoltaics, with a focus on two aspects. First, we examine non-toxic or less-toxic quantum dot materials designed for efficient thin-film based solar cells by considering factors such as bandgap tunability, exciton binding energy, and more. We then present the performance of quantum dot solar cells using these green quantum dot materials, and discuss the scientific and technological issues facing them. Second, we review fabrication methods of quantum dot thin films with low-cost, lowwaste, and non-toxic chemicals, for use in eco-friendly manufacturing processes.

We developed a high performance and wide active area ultraviolet (UV) photodiode from a normal silicon (Si) photodiode (SiPD) and UV-excited nanocrystal quantum dots (QDs). A thickness-controlled QD layer of 0.3–2.7 μm thickness was formed by a simple spraying and drying process to optimize UV detection. As a result, photocurrents 2.2–5.9 times higher than those of a bare SiPD were observed under UV light of 250–400 nm wavelength. The responsivity of the QD-coated SiPD was shown to reach to greater than 300% of the bare SiPD, and 150% of a gallium phosphide (GaP) UV PD. The effects of the thickness of the QD layer and the wavelength of incident light on UV detection were investigated according to the surface morphology analysis, and optical and photoluminescence characteristics of the deposited QD layers. We believe that the proposed technology opens the way to manufacturing cost-effective and high performance UV PDs that can be applied to UV-based chemical and biological sensing.

We have investigated poly (3-hexylthiophene) (P3HT) as a hole transport material interfacing PbS quantum dot and anode, and found that carrier separation is enhanced by increasing carrier concentration and mobility of P3HT. In addition, the ambient stability of PbS colloidal quantum dot solar cells are shown to be improved by surface oxidation of P3HT. Comparing with MoO3 anode interfacing material, P3HT performs better with controllable ambient stability. Electrode interfacing material should enable appropriate internal force for efficient carrier separation and enough carrier mobility to minimize carrier losses, which needs to provide a surface stabilization strategy to prevent degradation induced by ambient oxidation.

The enhancement of hot electron generation using plasmonic nanostructures is a promising strategy for developing photovoltaic devices. Here, we show that hot electron flow generated in plasmonic Au/TiO2 nanodiodes by incident light can be amplified when PbS quantum dots are deposited onto the surface of the nanodiodes. The effect is attributed to efficient extraction of hot electrons via a three-dimensional Schottky barrier, thus giving new pathways for hot electron transfer. We also demonstrate a correlation between the photocurrent and Schottky barrier height when using PbS quantum dots with varying size and ligand treatments that allow us to control the electric properties (e.g., band gap and Fermi level, respectively) of the PbS quantum dots. This simple method introduces a new technique for further improving the power conversion efficiency of thin-film photovoltaic devices.

Organic-inorganic hybrid photovoltaics (PVs) have recently attracted considerable attention as their PV performance has rapidly improved. Abnormal current-voltage (I-V) characteristics or I-V hysteresis, however, were occasionally observed in such systems that hampered the development of the PV technology. Here we study the hysteresis of organic-inorganic hybrid colloidal quantum dot (CQD) PVs by analyzing I-V characteristics upon systematic modulation of organic components of CQDs. We demonstrate that an external bias stress to CQD films transiently prompts redistribution of mobile ions, particularly protons of surface ligands, thus leading to the formation of a transient space-charge region in the CQD films. The variable space-charge region causes I-V hysteresis and photoinstability of CQD PVs, which is closely correlated with the transient behavior of mobile ions. Our findings here could provide significant implications to the understanding of the influence of mobile ions on I-V hysteresis in other organic-inorganic hybrid PVs such as perovskites.

In autonomous driving vehicles, the emergency braking system uses lidar or radar sensors to recognize the surrounding environment and prevent accidents. The conventional classifiers based on radar data using deep learning are single input structures using range–Doppler maps or micro-Doppler. Deep learning with a single input structure has limitations in improving classification performance. In this paper, we propose a multi-input classifier based on convolutional neural network (CNN) to reduce the amount of computation and improve the classification performance using the frequency modulated continuous wave (FMCW) radar. The proposed multi-input deep learning structure is a CNN-based structure using a distance Doppler map and a point cloud map as multiple inputs. The classification accuracy with the range–Doppler map or the point cloud map is 85% and 92%, respectively. It has been improved to 96% with both maps.

Controlled lateral quantum confinement in single-layer transition-metal chalcogenides (TMCs) can potentially combine the unique properties of two-dimensional (2D) exciton with the size-tunability of exciton energy, creating the single-layer quantum dots (SQDs) of 2D TMC materials. However, exploring such opportunities has been challenging due to the limited ability to produce well-defined SQDs with sufficiently high quality and size control, in conjunction with the commonly observed inconsistency in the optical properties. Here, we report an effective method to synthesize high-quality and size-controlled SQDs of WSe2 via multilayer quantum dots (MQDs) precursors, which enables grasping a clear picture of the role of lateral confinement on the optical properties of the 2D exciton. From the single-particle optical spectra and polarization anisotropy of WSe2 SQDs of varying sizes in addition to their ensemble data, we reveal how the properties of 2D exciton in single-layer TMCs evolve with increasing lateral...

We fabricated a hole transport layer (HTL) using transfer printing to fabricate high efficiency PbS quantum dot solar cell with minimized hysteresis. We applied PbS-EDT(1,2-ethanedithiol) as an HTL and controlled the adhesive properties between the donor substrate and the HTL through the UVO process in order to effectively transfer the HTL to the PbS layer, which enabled multilayer transfer printing as a result. During the transfer printing process, a gradient solid-solution layer was created at the interface with the existing PbS layer to reduce the hysteresis phenomenon, and to improve the power conversion efficiency to about 10% according to the HTL thickness optimization. In addition, the use of the EDT solvent can be remarkably reduced by using the transfer printing when forming the PbS-EDT layer. This can reduce the amount of organic solvent consumed in the process and improve the potential of environmentally friendly processes.

The luminescent down-shifting (LDS) layer, which transforms incoming high energy solar photons to visible ones, promises augmentation of both photoelectric performance and aesthetic appeals of photovoltaic (PV) modules. For efficient, colored PVs with LDS layer, luminophores with high photoluminescence quantum yield (PL QY), small overlap between absorption and emission spectra, and proven photostability are prerequisites. Here, we demonstrate colorful, opaque PV modules with LDS layers of minimized photon sacrifice enabled by structurally-engineered, eco-friendly InP/ZnSexS1-x quantum dots (QDs). Specifically, composition-controlled, thick shells allow enhanced absorption in the UV region and improved PL QY of QDs. Additionally, the ligand-engineering guarantees the stability of LDS layers after the damp heat test. Benefited from QD-LDS layers, commercially available CIGS and c-Si PV modules are awarded with 40% EQE enhancement in the ultraviolet region and wide-ranging color tunability over the entire visible region by QD-LDS layers. Hence, this integrated approach for desirable luminophores will contribute to the realization of highly-efficient, aesthetically-appealing opaque PV modules.

Quantum dots (QDs) are emerging photovoltaic materials that display exclusive characteristics that can be adjusted through modification of their size and surface chemistry. However, designing a QD-based optoelectronic device requires specialized approaches compared with designing conventional bulk-based solar cells. In this paper, design considerations for QD thin-film solar cells are introduced from two different viewpoints: optics and electrics. The confined energy level of QDs contributes to the adjustment of their band alignment, enabling their absorption characteristics to be adapted to a specific device purpose. However, the materials selected for this energy adjustment can increase the light loss induced by interface reflection. Thus, management of the light path is important for optical QD solar cell design, whereas surface modification is a crucial issue for the electrical design of QD solar cells. QD thin-film solar cell architectures are fabricated as a heterojunction today, and ligand exchange provides suitable doping states and enhanced carrier transfer for the junction. Lastly, the stability issues and methods on QD thin-film solar cells are surveyed. Through these strategies, a QD solar cell study can provide valuable insights for future-oriented solar cell technology.

In this report, we explore the underlying mechanisms by which doped organic thin films as a top hole-selective layer (HSL) improve the performance and stability of colloidal quantum dot (CQD)-based solar cells. Molecular dynamics-based theoretical studies prove that the hydro/oxo-phobic properties of the HSL serve to efficiently passivate the CQD solid. Furthermore, the robust and outstanding electrical properties of the HSL, simultaneously ensure a high power conversion efficiency (PCE) and increase the stability performance of CQD-based solar cells. As a result, a best PCE of 11.7% in a lead sulfide (PbS)-based CQD solar cell is achieved and over 90% of the initial performance is retained after 1 year storage under ambient conditions.

Using a combination of quantum dots (QDs) of different sizes, and thus different bandgaps, to extend the light-harvesting spectrum of a photovoltaic device in tandem architecture is a promising strategy for increasing the solar cell efficiency. In this study, we propose a new architecture for a solar cell device consisting of a graded-bandgap active layer made of lead sulfide QDs of different sizes and based on the structure of the Schottky junction. Colloidal PbS QDs with bandgaps of 1.55, 1.44, and 1.36 eV were synthesized and used to construct a series of Schottky junction solar cells. Cells with a graded-bandgap active layer exhibited an increase in short-circuit current density (Jsc) but yielded lower open-circuit voltage (Voc) compared with cells having a uniform bandgap. We found that adding a thin electron energy-boosting layer (EEB) made from 1.55-eV-bandgap QDs can partially compensate for the thermalization loss, and thus enhance Jsc and recover Voc. Consequently, this study provides a conceptual basis for further improvement in colloidal QD-based solar cells.

The PbS quantum dot is an emerging photovoltaic material, which may provide high efficiency breakthroughs. The most crucial element for the high efficiency solar cells's development is to understand charge transport characteristics of PbS quantum dot solids, which are also important in planning strategic research. We have investigated charge transport characteristics of PbS quantum dot solids thin films using space charge limited conduction analysis and assessed thickness dependent photovoltaic performances. The extracted carrier drift mobility was $low-10^{-2}cm^2/Vs$ with the estimated diffusion length about 50 nm. These and recently reported values were compared with those from a commercial photovoltaic material, and we present an essential element in further development of PbS quantum dot solids materials.

Using ultrafast transient absorption spectroscopy, we investigated the surface carrier trapping dynamics in various sized PbS quantum dots (QDs) when either a hot or cold exciton is photogenerated by different pump-energy. We observed that hot carriers exhibit distinctly different surface trapping dynamics from the cold exciton, in which their corresponding transient absorption (TA) spectral evolutions show clear differences in the long wavelength region (less than a band gap energy, Eg). We observed a rapid growth in the degree of surface trapping with an increase in the pump-energy. On the other hand, the degree of surface trapping in terms of the number of created excitons (⟨Nx⟩) shows negligible variation upon photoexcitation at any given wavelength. The photoinduced electron–hole separation followed by carrier trapping was characterized by ultrafast trapping rate. The surface trapping rate was solely dependent on the PbS QD size; the surface trapping rate becomes faster as the QD size increases. Furt...

A rapid increase in power conversion efficiencies in colloidal quantum dot (QD) solar cells has been achieved recently with lead sulphide (PbS) QDs by adapting a heterojunction architecture, which consists of small-area devices associated with a vacuum-deposited buffer layer with metal electrodes. The preparation of QD solar modules by low-cost solution processes is required to further increase the power-to-cost ratio. Herein we demonstrate all-solution-processed flexible PbS QD solar modules with a layer-by-layer architecture comprising polyethylene terephthalate (PET) substrate/indium tin oxide (ITO)/titanium oxide (TiO2)/PbS QD/poly(3-hexylthiophene) (P3HT)/poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS)/Ag, with an active area of up to 30 cm(2), exhibiting a power conversion efficiency (PCE) of 1.3% under AM 1.5 conditions (PCE of 2.2% for a 1 cm(2) unit cell). Our approach affords trade-offs between power and the active area of the photovoltaic devices, which results in a low-cost power source, and which is scalable to larger areas.

Indium antimonide (InSb), a narrow band gap III-V semiconductor is a promising infrared-active material for various optoelectronic applications. Synthetic challenge of colloidal InSb nanocrystals (NCs) lies in the limited choice of precursors. Only a few successful synthetic schemes involving highly toxic stibine (SbH3) or air- and moisture-sensitive metal silylamides (In[N(Si-(Me)3)2]3 or Sb[N(Si-(Me)3)2]3) as the precursor have been reported. We found that commercially available precursors InCl3 and Sb[NMe2]3 directly form highly crystalline colloidal InSb nanocrystals in the presence of a base such as LiN(SiMe3)2 or nBuLi. The mean size of the particles can be controlled by simply changing the activating base. This approach offers a one-pot synthesis of InSb NCs from readily available chemicals without the use of complex organometallic precursors.

In this work, photoluminescence from colloidal GaP nanocrystals (NCs) synthesized via a hot-injection method is observed and analyzed. The emission and excitation spectra of the GaP NCs indicate that two transitions, near the direct and indirect bandgaps of bulk GaP, are responsible for the luminescence.

Bandgap tunability and broadband absorption make quantum-dot (QD) photovoltaic cells (PVs) a promising candidate for future solar energy conversion systems. Approaches to improving the electrical properties of the active layer increase efficiency in part. The present study focuses on optical room for enhancement in QD PVs over wide spectrum in the near-infrared (NIR) region. We find that ray-optical light trapping schemes rather than the nanophotonics approach may be the best solution for enhancing broadband QD PVs by suppressing the escape probability of internal photons without spectral dependency. Based on the theoretical study of diverse schemes for various bandgaps, we apply a V-groove structure and a V-groove textured compound parabolic trapper (VCPT) to PbS-based QD PVs along with the measurement issues for PVs with a light scattering layer. The efficiency of the best device is improved from 10.3% to 11.0% (certified to 10.8%) by a V-groove structure despite the possibility of underestimation caused by light scattering in small-area devices (aperture area: 0.0625 cm2). By minimizing such underestimation, even greater enhancements of 13.6% and 15.6% in short circuit current are demonstrated for finger-type devices (0.167 cm2 without aperture) and large-area devices (2.10 cm2 with an aperture of 0.350 cm2), respectively, using VCPT.

Colloidal quantum dots (CQDs) have attracted attention as a next-generation of photovoltaics (PVs) capable of a tunable band gap and low-cost solution process. Understanding and controlling the surface of CQDs lead to the significant development in the performance of CQD PVs. Here we review recent progress in the realization of low-cost, efficient lead chalcogenide CQD PVs based on the surface investigation of CQDs. We focus on improving the electrical properties and air stability of the CQD achieved by material approaches and growing the power conversion efficiency (PCE) of the CQD PV obtained by structural approaches. Finally, we summarize the manners to improve the PCE of CQD PVs through optical design. The various issues mentioned in this review may provide insight into the commercialization of CQD PVs in the near future.

The size of colloidal quantum dot (CQD) materials and their surface modification by chemical ligands can change electronic properties thereby affecting device performances. In this study, direct measurement of the electronic structure within CQD thin film upon solid-state ligand exchange from oleic acid to 1,2-ethanedithiol has been made by photoelectron spectroscopy. Specifically, we analyzed valence band structures as a function of PbS CQD thickness on two kinds of substrates, indium tin oxide and titanium oxide, which give the trace of band bending and its saturation. Consequently, the energy-level alignment of the PbS CQD reveals downward band bending to the substrate but with different magnitude and depletion width depending on substrate. Wide depletion width and barrierless electron injection on TiO2 substrate indicate the importance of junction design and drift length for efficient CQD photovoltaics, which can be addressed discernibly via photoelectron spectroscopy.

We introduce a novel colloidal quantum dot solar cell (CQD SC) architecture, defined as inverted Schottky CQD SCs, which consists of a thin film of PbS CQDs sandwiched between a low-work-function, transparent conducting oxide (Lϕ-TCO) and a high-work-function metal anode. On Lϕ-TCO substrates, which were generated by coating a thin layer of polyethylenimine (PEI) onto FTO, a series of inverted Schottky CQD SCs with varied PbS CQD sizes and QD layer thicknesses were fabricated and characterized using capacitance–voltage (C–V), current–voltage (J–V), and external quantum efficiency (EQE). A Schottky junction, of about 180 nm in width, was formed at the front TCO contact, resulting in an EQE of approximately 70% in the short-wavelength region. The champion device reached 3.8% AM1.5 in power conversion efficiency, and retained efficiency over several weeks of air-exposure. A record open-circuit voltage (VOC) of 0.75 V was achieved by employing PbS CQDs of 1.56 eV in the bandgap. Advantages including the simple device structure, efficient carrier extraction, and air-stability demonstrated in this study suggest that inverted Schottky CQD SCs can reduce the price per Watt ratio and facilitate the development of CQD tandem solar cells.

ZnO thin films fabricated by a low-temperature sol–gel conversion method (L-ZnO) were employed as n-type electron-transporting layers (ETLs) in depleted-heterojunction quantum dot solar cells (DH-QDSCs). Thin films of PbS (∼200 nm) fabricated by spin-coating a colloidal PbS QD solution layer by layer were used as the p-type photoactive layers. The L-ZnO films functioned as efficient n-type ETLs by fully completely depleting the PbS active layers, and they displayed performances much higher than those of conventional ZnO nanoparticle-based ETLs. The morphologies and chemical compositions of the L-ZnO ETLs varied with the annealing conditions. These factors, in turn, had a marked effect on the charge-transfer characteristics at the L-ZnO/PbS interfaces of the DH-QDSCs. The power conversion efficiency (PCE) of the DH-QDSCs using the optimized L-ZnO films as ETLs was 3.93%, with the fill factor (FF) being 0.60, whereas the PCE of the cells using the ZnO nanoparticle-based films was 1.62%, with the FF being 0....

Near-infrared (NIR)-sensitive hybrid bulk heterojunction solar cells were developed using NIR-absorbing HgTe quantum dots (QDs) and a low-bandgap polymer, poly[2,6-(4,4′-bis-(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-alt-4,7(2,1,3-benzothiadiazole)] (PSBTBT). Hybrid composites of HgTe QDs and PSBTBT facilitate broad-range exploitation of the solar spectrum and efficient carrier dissociation prior to recombination. Nanostructures were formed on the surface of the hybrid composite via a nanoimprinting process using an anodic aluminum oxide (AAO) mold. This contributes to optical light scattering for efficient utilization of light up to the NIR region and enlarged photoactive layer–electrode interfacial areas for improving charge extraction, increasing the overall efficiency from 1.09 to 1.41%.

The optical properties and the carrier dynamics of CaSrSiO4:Eu3+ phosphors synthesized by using a solid-state reaction method have been studied by means of scanning electron microscopy, X-ray diffraction, photoluminescence (PL), PL excitation, time-resolved PL, and PL quantum-yield measurements. The phosphor synthesized with a Eu concentration of 5% and sintered at 1380 °C for 2 h in air showed a high quantum yield of 88.53% and good CIE chromaticity coordinate values. The strong excitation bands observed at 395 nm (7F0-5L6) and 466 nm (7F0-5D2) lead to an intense 5D0-7F2 transition (614 nm). The forbidden transitions (5D0-7F0 and 5D0-7F2) were observed and showed lifetimes shorter than that of the magnetic dipole transition (5D0-7F1).

Here we report on heterojunction PbS quantum dot (QD) solar cells using RF magnetron sputtered CdS as the n-type window layer. These solar cells generate large open circuit voltage compared to previously reported PbS-QD solar cells. Our investigations of this device design show an optimized CdS film thickness of 70 nm and an optimized PbS QD diameter of ∼2.7 nm, corresponding to a bandgap energy of ∼1.57 eV. Under simulated AM1.5 G illumination, we attain short circuit current as high as 12 mA-cm � 2

The improvement of power conversion efficiency, especially current density (Jsc), for nanocrystal quantum dot based heterojunction solar cells was realized by employing a trenched ZnO film fabricated using nanoimprint techniques. For an optimization of ZnO patterns, various patterned ZnO films were investigated using electrical and optical analysis methods by varying the line width, interpattern distance, pattern height, and residual layer. Analyzing the features of patterned ZnO films allowed us to simultaneously optimize both the pronounced electrical effects as well as optical properties. Consequently, we achieved an enhancement in Jsc from 7.82 to 12.5 mA cm(-2) by adopting the patterned ZnO with optimized trenched shape.

Ambient stability of colloidal nanocrystal quantum dots (QDs) is imperative for low-cost, high-efficiency QD photovoltaics. We synthesized air-stable, ultrasmall PbS QDs with diameter (D) down to 1.5 nm, and found an abrupt transition at D ≈ 4 nm in the air stability as the QD size was varied from 1.5 to 7.5 nm. X-ray photoemission spectroscopy measurements and density functional theory calculations reveal that the stability transition is closely associated with the shape transition of oleate-capped QDs from octahedron to cuboctahedron, driven by steric hindrance and thus size-dependent surface energy of oleate-passivated Pb-rich QD facets. This microscopic understanding of the surface chemistry on ultrasmall QDs, up to a few nanometers, should be very useful for precisely and accurately controlling physicochemical properties of colloidal QDs such as doping polarity, carrier mobility, air stability, and hot-carrier dynamics for solar cell applications.

Chemically synthesized InP nanocrystals (NCs) are drawing a large interest as a potentially less toxic alternative to CdSe-based nanocrystals. With a bulk band gap of 1.35 eV and an exciton Bohr radius of ∼10 nm the emission wavelength of InP NCs can in principle be tuned throughout the whole visible and near-infrared range by changing their size. Furthermore, a few works reported fluorescence quantum yields exceeding 70% after overcoating the core NCs with appropriate shell materials. Therefore, InP NCs are very promising for use in lighting and display applications. On the other hand, a number of challenges remain to be addressed in order to progress from isolated research results to robust and reproducible synthesis methods for high quality InP NCs. First of all, the size distribution of the as-synthesized NCs needs to be reduced, which directly translates into more narrow emission line widths. Next, reliable protocols are required for achieving a given emission wavelength at high reaction yield and fo...

Nanomechanical Systems Research Division, Korea Institute of Machinery and Materials, Daejeon 305-343, Korea Received October 22, 2011, Accepted February 1, 2012InP quantum dot (QD)-organosilicon nanocomposites were synthesized and their photoluminescencequenching was mainly investigated because of their applicability to white LEDs (light emitting diodes). Theas-synthesized InP QDs are capped with myristic acid (MA), which are incompatible with typical siliconeencapsulants. We have introduced a new ligand, 3-aminopropyldimethylsilane (APDMS), which enablesembedding the QDs into vinyl-functionalized silicones through direct chemical bonding. The exchange ofligand from MA to APDMS does not significantly affect the UV absorbance of the InP QDs, but quenches thePL to about 10% of its original value with the relative increase in surface related emission intensities, which isexplained by stronger coordination of the APDMS ligands to the surface indium atoms. InP QD-organosiliconnanocomposites were synthesized by connecting the QDs using a short cross-linker such as 1,4-divinyl-tetramethylsilylethane (DVMSE) by the hydrosilylation reaction. The formation and changes in the opticalproperties of the InP QD-organosilicon nanocomposite were monitored by ultraviolet visible (UV-vis)absorbance and steady state photoluminescence (PL) spectroscopies. As the hydrosilylation reaction proceeds,the QD-organosilicon nanocomposite is formed and grows in size, causing an increase in the UV-visabsorbance due to the scattering effect. At the same time, the PL spectrum is red-shifted and, very interestingly,the PL is quenched gradually. Three PL quenching mechanisms are regarded as strong candidates for the PLquenching of the QD nanocomposites, namely the scattering effect, Forster resonance energy transfer (FRET)and cross-linker tension preventing the QD’s surface relaxation. Key Words : InP quantum dot, Organosilicon, Nanocomposite, PL quenching, Ligand exchangeIntroductionA semiconductor quantum dot (QD) is a nano-sized,crystalline particle consisting of hundreds to thousands ofatoms, falling in the gap between molecular cluster and bulkcrystal.

This paper reports on the enhanced photoluminescence (PL) of nanocomposites through the layered structuring of phosphor and quantum dot (QD). Green phosphor of Sr2SiO4:Eu, red QDs of CdSe/CdS/CdZnS/ZnS core-multishell, and thermo-curable resin were used for this study. Two kinds of composite (layered and mixed) were prepared, and the schemes for optical energy transfer between QD and phosphor were suggested and investigated based on PL decay characteristics. It was found that the layered structure is more effective than the mixed one with respect to PL intensity, PL decay, and thermal loss. When this layered nanocomposite (QDs on phosphor) is used to make a white light emitting diode (LED), the brightness is increased by 37%, and the color rendering index (CRI) value is raised to 88.4 compared to the mixed case of 80.4.

Electrical conductivity in quantum dot solids is crucial for application in devices. In addition to the well-known ligand exchange strategies for enhanced conductivity, the current study examined the optical, structural, and electrical properties of ethanedithiol-treated layer-by-layer (LbL) assembled quantum dot solid (QDS) films following low-temperature annealing (room temperature to 170 °C). As the annealing temperature increased, it was induced that the average separation between nanocrystal quantum dots is decreased, and accordingly, the overall conductivity of the QDS increased exponentially. From a simplified percolation model, the activation energy of temperature-dependent quantum dot attachment was estimated to be around 0.26−0.27 eV both for PbS and PbSe quantum dot solids. Furthermore, the results of this study indicated that device applications requiring higher conductivity, attainable through high-temperature annealing, may also require repassivation after annealing.

A novel self-charging platform is proposed using colloidal-quantum-dot (CQD) photovoltaics (PVs) via the near-infrared (NIR) band for low-power electronics. Low-bandgap CQDs can convert invisible NIR light sources to electrical energy more efficiently than wider spectra because of reduced thermalization loss. This energy-conversion strategy via NIR photons ensures an enhanced photostability of the CQD devices. Furthermore, the NIR wireless charging system can be concealed using various colored and NIR-transparent fabric or films, providing aesthetic freedom. Finally, an NIR-driven wireless charging system is demonstrated for a wearable healthcare bracelet by integrating a CQD PVs receiver with a flexible lithium-ion battery and entirely embedding them into a flexible strap, enabling permanent self-charging without detachment.

In this paper, we fabricated quantum dot (QD) aggregates at desired locations using dielectrophoretic (DEP) forces induced in the carbon nanotube (CNT) nanogap created by Joule heating-induced electrical breakdown. Nanogaps with a size of at least 20–30 nm can be effectively fabricated in the ambient condition, and fabrication yield can be monitored through in-situ electrical signal without post morphological analysis. The geometry of CNT electrodes with high aspect ratio as well as the gap size of the electrodes to a few tens of nanometers scale enabled the derivation of sufficiently high DEP forces that facilitate the trapping of QD in the CNT nanogap. Above all, we were able to fabricate a conducting crack-free QD aggregates by exchanging the ligands on the surface of the QDs in the presence of a DEP force and this approach showed the possibility of being applied as a QD based optoelectronic devices.

In this paper, we fabricated the optoelectronic device based on Cadmium selenide(CdSe) nanocrystal quantum dots (NQDs)/single-walled carbon nanotubes(SWNTs) heterostructure using dieletrophoretic force. The efficient charge transfer phenomena from CdSe to SWNT make CdSe-Pyridine(py)-SWNT unique heterostructures for novel optoelectronic device. The conductivity of CdSe-py-SWNT was increased when it was exposed at ultra violet(UV) lamp, and varied as a function of wavelength of incident light.

Colloidal InAs quantum wires having diameters in the range of 5-57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution-liquid-solid (SLS) mechanism. The diameter dependence of the effective band gaps (DeltaE(g)s) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The DeltaE(g) values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d(-1)), whereas the simplest confinement models predict that DeltaE(g) should scale with inverse-square diameter (d(-2)). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band-conduction-band coupling in the narrow-gap InAs semiconductor.

We fabricated heterojunction solar cells with PbSe/PbS core shell quantum dots and studied the precisely controlled PbS shell thickness dependency in terms of optical properties, electronic structure, and solar cell performances. When the PbS shell thickness increases, the short circuit current density (JSC) increases from 6.4 to 11.8 mA cm(-2) and the fill factor (FF) enhances from 30 to 49% while the open circuit voltage (VOC) remains unchanged at 0.46 V even with the decreased effective band gap. We found that the Fermi level and the valence band maximum level remain unchanged in both the PbSe core and PbSe/PbS core/shell with a less than 1 nm thick PbS shell as probed via ultraviolet photoelectron spectroscopy (UPS). The PbS shell reduces their surface trap density as confirmed by relative quantum yield measurements. Consequently, PbS shell formation on the PbSe core mitigates the trade-off relationship between the open circuit voltage and the short circuit current density. Finally, under the optimized conditions, the PbSe core with a 0.9 nm thick shell yielded a power conversion efficiency of 6.5% under AM 1.5.

We developed a single step, cation-exchange reaction that produces air-stable PbSe quantum dots (QDs) from ZnSe QDs and PbX2 (X = Cl, Br, or I) precursors. The resulting PbSe QDs are terminated with halide anions and contain residual Zn cations. We characterized the PbSe QDs using UV–vis–NIR absorption, photoluminescence quantum yield spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Solar cells fabricated from these PbSe QDs obtained an overall best power conversion efficiency of 6.47% at one sun illumination. The solar cell performance without encapsulation remains unchanged for over 50 days in ambient conditions; and after 50 days, the National Renewable Energy Laboratory certification team certified the device at 5.9%.

We developed a novel and easy encapsulation method for quantum dots (QDs) using a partially oxidized semi-crystalline polymeric material which forms a micron-sized granule with a multi-lamellar structure from a dilute solution. The QDs were highly dispersed in the granule in such a way that they were adsorbed on the lamella with ∼12 nm spacing followed by lamellar stacking. The QDs were heavily loaded into the granule to 16.7 wt% without aggregation, a process which took only a few minutes. We found that the quantum yield of the QDs was not degraded after the encapsulation. The encapsulated QD-silicone composite exhibited excellent long-term photo- and thermal stability with its initial photoluminescence intensity maintained after blue LED light radiation for 67 days and storage at 85 °C and 85% relative humidity for 119 days.

The purpose of this study was to evaluate the effect of bicycle saddle shape on penile blood flow during cycling. Penile blood flow was measured using a laser Doppler flowmeter in 20 potent male volunteers. In a counterbalanced, crossover design, measurements were taken in the standing and sitting positions, on either a narrow unpadded or wide unpadded saddle, before and after cycling for 5 min. Before cycling, penile blood flow (ml/min/100 g tissue) was significantly decreased from 1.6+/-0.7 to 1.5+/-0.7 (P=0.010) on the wide saddle and from 1.7+/-0.6 to 1.0+/-0.5 (P

The recent success of the surface passivation of lead chalcogenide quantum dots for enhancing ambient stability offers further investigation of surface states in air. Here we studied the photoresponses due to surface passivation and oxygen, thus providing the relations of surface states and the photoresponse of PbSe QD films by monitoring the changes in QD film with air exposure. A dramatic near-infrared photoresponse was observed when the PbSe film stabilized through surface passivation was exposed to air. As a result of estimating the density of trap states from the FET characteristics, it was confirmed that the iodide-passivated PbSe film exposed to the air had more trap states than the nitrogen atmosphere. The increase of the trap state due to oxygen adsorption led to the increase of the trap-captured photogenerated electrons, which increased the photoconduction gain. Even though some trap states have a negative impact on device parameters such as charge mobility and response time, controlling the oxygen-related trap states on QD surface is expected to enhance the photoresponsivity on the QD-based photoconductive films without performance degradation in air.

Colloidal quantum dots (CQDs) are promising light harvesting materials for realization of solution processible, highly efficient multipurpose photovoltaics (PVs). Here, PbS CQD solar cells are reported with improved certified power conversion efficiency performance of 10.4% by simply controlling protic solvents (alcohols) in ligand exchange process. With shorter chain alcohols, the mobility of charge carriers is an order-of-magnitude improved due to the enhanced interparticle coupling; on the other hand, excessive removal of passivating ligands by very protic solvent, methanol (MeOH) induced undesirable traps on CQD surface. Consequently, it has been found that high performance CQD PVs require a solvent engineering for balance between native leaving ligands with incoming ligands during ligand exchange process for well-controlled surfaces of CQDs and enhanced carrier concentration of conductive CQD films.

Colloidal III-V semiconductor nanocrystal quantum dots [NQDs] have attracted interest because they have reduced toxicity compared with II-VI compounds. However, the study and application of III-V semiconductor nanocrystals are limited by difficulties in their synthesis. In particular, it is difficult to control nucleation because the molecular bonds in III-V semiconductors are highly covalent. A synthetic approach of InP NQDs was presented using newly synthesized organometallic phosphorus [P] precursors with different functional moieties while preserving the P-Si bond. Introducing bulky side chains in our study improved the stability while facilitating InP formation with strong confinement at a readily low temperature regime (210°C to 300°C). Further shell coating with ZnS resulted in highly luminescent core-shell materials. The design and synthesis of P precursors for high-quality InP NQDs were conducted for the first time, and we were able to control the nucleation by varying the reactivity of P precursors, therefore achieving uniform large-sized InP NQDs. This opens the way for the large-scale production of high-quality Cd-free nanocrystal quantum dots.