Colloidal quantum dot materials for next-generation near-infrared optoelectronics.

Colloidal quantum dots (CQDs) are a promising class of materials for next-generation optoelectronic devices, such as displays, LEDs, lasers, photodetectors, and solar cells. CQDs can be obtained at low cost and in large quantities using wet chemistry. CQDs have also been produced using various materials, such as CdSe, InP, perovskites, PbS, PbSe, and InAs. Some of these CQD materials absorb and emit photons in the visible region, making them excellent candidates for displays and LEDs, while others interact with low-energy photons in the near-infrared (NIR) region and are intensively utilized in NIR lasers, NIR photodetectors, and solar cells. In this review, we have focused on NIR CQD materials and reviewed the development of CQD materials for solar cells, NIR lasers, and NIR photodetectors since the first set of reports on CQD materials in these particular applications.

FOSS-Based Method for Thin-Walled Structure Deformation Perception and Shape Reconstruction.

To improve the accuracy of deformation perception and shape reconstruction of flexible thin-walled structures, this paper proposes a method based on the combination of FOSS (fiber optic sensor system) and machine learning. In this method, the sample collection of strain measurement and deformation change at each measuring point of the flexible thin-walled structure was completed by ANSYS finite element analysis. The outliers were removed by the OCSVM (one-class support vector machine) model, and the unique mapping relationship between the strain value and the deformation variables (three directions of x-, y-, and z-axis) at each point was completed by a neural-network model. The test results show that the maximum error of the measuring point in the direction of the three coordinate axes: the x-axis is 2.01%, the y-axis is 29.49%, and the z-axis is 15.52%. The error of the coordinates in the y and z directions was large, and the deformation variables were small, the reconstructed shape had good consistency with the deformation state of the specimen under the existing test environment. This method provides a new idea with high accuracy for real-time monitoring and shape reconstruction of flexible thin-walled structures such as wings, helicopter blades, and solar panels.

Deep learning enabled inverse design of nanocrystal-based optical diffusers for efficient white LED lighting.

Angular color uniformity and luminous flux are the most important figures of merit for a white-light-emitting diode (WLED), and simultaneous improvement of both figures of merit is desired. The cellulose-nanocrystal (CNC)-based optical diffuser has been applied on the WLED module to enhance angular color uniformity, but it inevitably causes the reduction of luminous flux. Here we demonstrate a deep-learning-based inverse design approach to design CNC-coated WLED modules. The developed forward neural network successfully predicts two figures of merit with high accuracy, and the inverse predicting model can rapidly design the structural parameters of CNC film. Further explorations taking advantage of both forward and inverse neutral networks can effectively construct the coating layer for WLED modules to reach the best performance.

Transcriptome Analysis of Stephania tetrandra and Characterization of Norcoclaurine-6-O-Methyltransferase Involved in Benzylisoquinoline Alkaloid Biosynthesis.

Stephania tetrandra (S. Moore) is a source of traditional Chinese medicine that is widely used to treat rheumatism, rheumatoid arthritis, edema, and hypertension. Benzylisoquinoline alkaloids (BIAs) are the main bioactive compounds. However, the current understanding of the biosynthesis of BIAs in S. tetrandra is poor. Metabolite and transcriptomic analyses of the stem, leaf, xylem, and epidermis of S. tetrandra were performed to identify candidate genes associated with BIAs biosynthesis. According to the metabolite analysis, the majority of the BIAs accumulated in the root, especially in the epidermis. Transcriptome sequencing revealed a total of 113,338 unigenes that were generated by de novo assembly. Among them, 79,638 unigenes were successfully annotated, and 42 candidate structural genes associated with 15 steps of BIA biosynthesis identified. Additionally, a new (S)-norcoclaurine-6-O-methyltransferase (6OMT) gene was identified in S. tetrandra, named St6OMT2. Recombinant St6OMT2 catalyzed (S)-norcoclaurine methylation to form (S)-coclaurine in vitro. Maximum activity of St6OMT2 was determined at 30°C and pH 6.0 in NaAc-HAc buffer. Its half-life at 50°C was 22 min with the Km and kcat of 28.2 µM and 1.5 s-1, respectively. Our results provide crucial transcriptome information for S. tetrandra, shedding light on the understanding of BIAs biosynthesis and further gene functional characterization.

Silicon Surface Passivation for Silicon-Colloidal Quantum Dot Heterojunction Photodetectors.

Sensitizing crystalline silicon (c-Si) with an infrared-sensitive material, such as lead sulfide (PbS) colloidal quantum dots (CQDs), provides a straightforward strategy for enhancing the infrared-light sensitivity of a Si-based photodetector. However, it remains challenging to construct a high-efficiency photodetector based upon a Si:CQD heterojunction. Herein, we demonstrate that Si surface passivation is crucial for building a high-performance Si:CQD heterojunction photodetector. We have studied one-step methyl iodine (CH3I) and two-step chlorination/methylation processes for Si surface passivation. Transient photocurrent (TPC) and transient photovoltage (TPV) decay measurements reveal that the two-step passivated Si:CQD interface exhibits fewer trap states and decreased recombination rates. These passivated substrates were incorporated into prototype Si:CQD infrared photodiodes, and the best performance photodiode based upon the two-step passivation shows an external quantum efficiency (EQE) of 31% at 1280 nm, which represents a near 2-fold increase over the standard device based upon the one-step CH3I passivated Si.

Current Advance of Immune Evasion Mechanisms and Emerging Immunotherapies in Renal Cell Carcinoma.

Renal cell carcinoma is a highly heterogeneous cancer group, and the complex microenvironment of the tumor provides appropriate immune evasion opportunities. The molecular mechanism of immune escape in renal cell carcinoma is currently a hot issue, focusing primarily on the major complex of histocompatibility, immunosuppressive cells, their secreted immunosuppressive cytokines, and apoptosis molecule signal transduction. Immunotherapy is the best treatment option for patients with metastatic or advanced renal cell carcinoma and combination immunotherapy based on a variety of principles has shown promising prospects. Comprehensive and in-depth knowledge of the molecular mechanism of immune escape in renal cell carcinoma is of vital importance for the clinical implementation of effective therapies. The goal of this review is to address research into the mechanisms of immune escape in renal cell carcinoma and the use of the latest immunotherapy. In addition, we are all looking forward to the latest frontiers of experimental combination immunotherapy.

Design and Measurement of a Dual FBG High-Precision Shape Sensor for Wing Shape Reconstruction.

FBG shape sensors based on soft substrates are currently one of the research focuses of wing shape reconstruction, where soft substrates and torque are two important factors affecting the performance of shape sensors, but the related analysis is not common. A high-precision soft substrates shape sensor based on dual FBGs is designed. First, the FBG soft substrate shape sensor model is established to optimize the sensor size parameters and get the optimal solution. The two FBG cross-laying method is adopted to effectively reduce the influence of torque, the crossover angle between the FBGs is 2α, and α = 30° is selected as the most sensitive angle to the torquer response. Second, the calibration test platform of this shape sensor is built to obtain the linear relationship among the FBG wavelength drift and curvature, rotation radian loaded vertical force and torque. Finally, by using the test specimen shape reconstruction test, it is verified that this shape sensor can improve the shape reconstruction accuracy, and that its reconstruction error is 6.13%, which greatly improves the fit of shape reconstruction. The research results show that the dual FBG high-precision shape sensor successfully achieves high accuracy and reliability in shape reconstruction.

An Adaptive Multi-Dimensional Vehicle Driving State Observer Based on Modified Sage-Husa UKF Algorithm.

An accurate vehicle driving state observer is a necessary condition for a safe automotive electronic control system. Vehicle driving state observer is challenged by unknown measurement noise and transient disturbances caused by complex working conditions and sensor failure. For the classical adaptive unscented Kalman filter (AUKF) algorithm, transient disturbances will cause the failure of state estimation and affect the subsequent process. This paper proposes an AUKF based on a modified Sage-Husa filter and divergence calculation technique for multi-dimensional vehicle driving state observation. Based on the seven-degrees-of-freedom vehicle model and the Dugoff tire model, the proposed algorithm corrects the measurement noise by using modified Sage-Husa maximum posteriori. To reduce the influence of transient disturbance on the subsequent process, covariance matrix is updated after divergence is detected. The effectiveness of the algorithm is tested on the double lane change and Sine Wave road conditions. The robustness of the algorithm is tested under severe transient disturbance. The results demonstrate that the modified Sage-Husa UKF algorithm can accurately detect transient disturbance and effectively reduce the resulted accumulated error. Compared to classical AUKF, our algorithm significantly improves the accuracy and robustness of vehicle driving state estimation. The research in this paper provides a reference for multi-dimensional data processing under changeable vehicle driving states.

Unusual Surface Ligand Doping-Induced p-Type Quantum Dot Solids and Their Application in Solar Cells.

Doping quantum dots (QDs) is a problem that has been haunting researchers in the QD research community for years, even though doping techniques have been utilized for decades in conventional semiconductors. For the "self-purification" in colloidal QDs, engineering the surface ligands has emerged as an effective way to alter free carrier concentrations and doping types in colloidal QD solids. Halide-atomic ligands are the most popular ligands in producing PbS QD solids since they provide minimal dot-to-dot distance while maintain low in-gap trap states. However, previously reported halide surface treatment could only produce n-type QD solids. Here, we report the fabrication of p-type PbS QD solids using proton-assisted surface ligand exchange. We unveiled the origin of p-type doing in PbS QD solids, and it came from an unusual surface ligand; the HOH+ group formed using NH4X (X = Cl, Br, I) in methanol. We further fabricated QD solar cells using PbS-NH4Cl, a p-type QD solid predicted and proved by our theory and experiments. The champion device shows a high power conversion efficiency of 7.49%.

Nanocrystal-filled polymer for improving angular color uniformity of phosphor-converted white LEDs.

Improvement in angular color uniformity is of significant importance to reach high illumination quality for a white LED. In this demonstration, we show potential applications of cellulose-nanocrystal (CNC)-filled polymer for enhancing color uniformity of white LEDs. The excellent optical diffusion capability provided by CNC and the mechanical flexibility offered by the polymer matrix render it a highly efficient color mixer. The CNC-filled polymer was applied on the outer surface of a conventional white LED module to enhance both color and illumination uniformities. It reduced 71.4% of angular color deviation and improved illumination uniformity by 35.5% while maintaining over 85% of light energy transmission. We also demonstrate that for a specific application purpose, such as downlight illumination, one can simultaneously achieve high color uniformity and downlight illumination with reduced glare by constructing the CNC-filled polymer into a CNC-doped lens. In this case, a 0.03%-CNC-filled lens can reduce angular color deviation by 74.0% and achieve a light energy transmission of 85.5%. The light energy transmission can be further improved by advanced lens designs for energy-saving purposes.

Surface-Modified Substrates for Quantum Dot Inks in Printed Electronics.

Printed electronics fill the niches for low-cost, flexible devices in electronics. Developing substrates suitable for various printable electronic inks becomes an important topic in both academia and industry. Because of their extraordinary properties like solution processability, colloidal quantum dots (QDs) are gradually emerging in this field as promising candidates for electronic inks. In recent years, researchers have successfully produced high quality PbS QD inks in polar solvents. However, the incorporation of electronic inks onto a well-passivated substrate remains challenging due to the processing incompatibility between polar solvents and hydrophobic substrates. Here, we propose a surface modification strategy by using chlorine to achieve both trap-site suppression and a hydrophilic surface. The chlorine can effectively passivate the surface dangling bonds and charged hydroxyls while creating a hydrophilic surface. On this modified substrate, the contact angle between the water droplet and the SiO2 substrate can be as small as 20° and this strategy is also feasible for other polymer and inorganic substrates. For a proof-of-concept demonstration, we fabricated a PbS QD ink-based field-effect transistor on a Cl-passivated substrate, and the device showed a mobility as high as 4.36 × 10-3 cm2/V s, which indicates effective trap-site suppression. This device also enables the potential of the Cl-passivated substrates for QD inks with water or other polar solvents.

Control of Femtoliter Liquid on a Microlens: A Way to Flexible Dual-Microlens Arrays.

Microlens arrays are key elements for light management in optoelectronic devices. The recent advancement in the wearable intelligent electronics has driven the development of flexible microlenses. In this work, we show a controllable and scalable surface-droplet-based strategy to create unconventional flexible polymer microlens arrays. The technique is underpinned by the morphological transition of femtoliter liquid on the surface of a microlens surrounded by a planar area. We found that the droplet liquid wetted the rim of the microlens first and gradually moved upward to the microlens surface with an increase in the liquid volume. The morphology evolution of the droplet is in good agreement with the predication from our simulations based on the interfacial energy minimization under the condition of the pinned boundary. The shape of the droplet on the microlens is well controlled by the droplet volume, aspect ratio of the microlens, and the interfacial energy of the droplets on the microlens. As a result, the obtained structures of one microlens partially covered by a droplet can be produced in arrays over a large scale, serving as templates for fabricating transparent polymer double microlens arrays for improved light emission from the optoelectronic device.

Reducing shadowing losses in silicon solar cells using cellulose nanocrystal: polymer hybrid diffusers.

Gridline shadowing is one of the main factors affecting the performance of silicon solar cells. In this demonstration, a straightforward, scalable approach is reported to reduce shadowing losses from metallic contacts on silicon solar cells by employing cellulose nanocrystals (CNC) mixed in a polymer- polydimethylsiloxane. The method is highly compatible with current solar cell module manufacturing. The CNC:polymer (CNP) hybrid diffusers, offering highly efficient broadband light diffusion, are applied atop the metallization areas to deflect the light impinging on metallic gridlines toward uncovered active areas on the solar cell. Simulations showed that the CNP diffuser is an excellent candidate for reducing shadowing losses within a wide range of incident angles, as it can reduce more than 30% of shadowing losses at normal incidence, and nearly 50% of the lost light can be recycled at the incident angle of 60°. Taking advantage of reduced shadowing losses, a new 6-busbar technology based on the CNP diffusers is proposed with lower manufacturing complexity and higher overall efficiency.

On-chip colloidal quantum dot devices with a CMOS compatible architecture for near-infrared light sensing.

Solution-processed semiconductors that exhibit tunable light absorption and can be directly integrated into state-of-the-art silicon technologies are attractive for near-infrared (NIR) light detection in applications of medical imaging, night vision cameras, hyperspectral sensing, etc. Colloidal quantum dot (CQD) is regarded as a promising candidate for its solution-processability and superior optoelectronic properties. Here we propose an on-chip CQD photodetector, photodiode-oxide-semiconductor field-effect transistor, for NIR light sensing. This CMOS compatible device architecture utilizes silicon as a channel for carrier transport and PbS CQD as the light absorbing material controlling the channel conductivity. While the light with a wavelength longer than about 1100 nm cannot excite a photocurrent in commercial silicon-based photodetectors due to the absorption cutoff of silicon, the proposed photodetector can have responses owing to the usage of a PbS CQD photodiode. Simulations showed that the photodiode could provide photovoltage to the semiconductor, forming an inversion layer at the oxide-semiconductor interface, and the electron density at the interface is significantly enhanced. As a result, currents could flow through this layer with ease between the source and drain electrodes. For a proof-of-concept demonstration, we experimentally connected a CQD photodiode with a commercial silicon transistor and proved that the current from the transistor could be increased by photovoltage provided by the photodiode under NIR light illumination. The device shows a responsivity of 5.9A/W at the wavelength of 1250 nm.

Cu(ii)/Ni(ii)-organic frameworks constructed from the homometallic clusters by 5-(2-carboxyphenoxy)isophthalic acid and N-ligand: synthesis, structures and visible light-driven photocatalytic properties.

Four new complexes, namely, Cu2(O-cpia)(btb)0.5·(OH) (1), Cu3(O-cpia)2(bpy)2 (2), [Ni2(O-cpia)(phen)·(OH)·H2O]·2H2O (3) and [Ni3(O-cpia)2(bpy)3·2H2O]·2H2O (4) (O-cpia = 5-(2-carboxyphenoxy)isophthalic acid, btb = 1,4-bis(1,2,4-triazol-1-yl)butane, bpy = 4,4'-bipyridine) were successfully isolated under hydrothermal conditions. The four complexes exhibit different architectures constructed from different homometallic clusters varying from mononuclear, binuclear to tetranuclear metal(ii) polyhedra as Second Building Blocks (SBUs). 1 features a 3D framework constructed from the tetranuclear clusters [Cu4(µ3-OH)2] as SBUs, linked with Cu(1)O4N and Cu(2)O5 polyhedra by O-cpia/btb mixed linkers. 2 also exhibits a 3D structure based on trinuclear clusters [Cu3(COO)4] SBUs, bridged with Cu(1)O3N2 and Cu(2)O4 polyhedra via O-cpia/bpy mixed ligands. 3 shows a 2D network consisting of tetranuclear clusters [Ni4(µ3-OH)2] SBUs, which are bridged with Ni(1)O4N2 and Ni(2)O6 through O-cpia ligands. It is worth noting that 4, with a 3D structure, is generated from the binuclear clusters [Ni2(COO)4] (Ni(1)O4N) and mononuclear metal Ni(2) cores (Ni(2)O4N2) as SBUs, and bridged by O-cpia/bpy mixed ligands. Meanwhile, the degradation of dyes (RhB) by the complexes under visible light irradiation was studied. 1-4 are semiconducting in nature, with E g of 1.30 eV (1), 1.78 eV (2), 2.85 eV (3) and 2.14 eV (4). Cu(ii) complexes 1 and 2 are highly efficient photocatalysts for the degradation of RhB under visible light irradiation.

Correction: Cu(ii)/Ni(ii)-organic frameworks constructed from the homometallic clusters by 5-(2-carboxyphenoxy)isophthalic acid and N-ligand: synthesis, structures and visible light-driven photocatalytic properties.

[This corrects the article DOI: 10.1039/C9RA01496A.].

Extraordinary Focusing Effect of Surface Nanolenses in Total Internal Reflection Mode.

Microscopic lenses are paramount in solar energy harvesting, optical devices, and imaging technologies. This work reports an extraordinary focusing effect exhibited by a surface nanolens (i.e., with at least one dimension of subwavelength) that is situated in an evanescent field from the total internal reflection (TIR) of light illuminated to the supporting substrate above the critical angle. Our measurements show that the position, shape, and size of the surface area with enhanced light intensity are determined by the geometry of the nanolens and the incident angle, in good agreement with simulation results. This strong focusing effect of the surface nanolens is shown to significantly promote the plasmonic effect of deposited gold nanoparticles on the lens surface inlight conversion and to vaporize surrounding water to microbubbles by using low laser power. This work further demonstrates that the light redistribution by the surface nanolens in TIR enables a range of novel applications in selectively local visualization of specimens in fluorescence imaging, optical trapping of colloids from an external flow, and selective materials deposition from photoreactions.

Inverse Opal Photonic Crystals as an Optofluidic Platform for Fast Analysis of Hydrocarbon Mixtures.

Most of the reported optofluidic devices analyze liquid by measuring its refractive index. Recently, the wettability of liquid on various substrates has also been used as a key sensing parameter in optofluidic sensors. However, the above-mentioned techniques face challenges in the analysis of the relative concentration of components in an alkane hydrocarbon mixture, as both refractive indices and wettabilities of alkane hydrocarbons are very close. Here, we propose to apply volatility of liquid as the key sensing parameter, correlate it to the optical property of liquid inside inverse opal photonic crystals, and construct powerful optofluidic sensors for alkane hydrocarbon identification and analysis. We have demonstrated that via evaporation of hydrocarbons inside the periodic structure of inverse opal photonic crystals and observation of their reflection spectra, an inverse opal film could be used as a fast-response optofluidic sensor to accurately differentiate pure hydrocarbon liquids and relative concentrations of their binary and ternary mixtures in tens of seconds. In these 3D photonic crystals, pure chemicals with different volatilities would have different evaporation rates and can be easily identified via the total drying time. For multicomponent mixtures, the same strategy is applied to determine the relative concentration of each component simply by measuring drying time under different temperatures. Using this optofluidic sensing platform, we have determined the relative concentrations of ternary hydrocarbon mixtures with the difference of only one carbon between alkane hydrocarbons, which is a big step toward detailed hydrocarbon analysis for practical use.

Analysis of three-dimensional interference patterns of an inclined capillary.

We study the interference patterns from an inclined capillary tube filled with liquid by using the ray tracing method and interference theory. A beautiful elliptical pattern is found on the screen, with refined fringes embedded in it. Particularly, the fringes on top of the pattern are continuously swallowed to the center with the angle of incidence increasing. In addition, a method is demonstrated to determine the refractive index of the liquid and the wavelength of the incident light by measuring the capillary tilt of every 10-fringe being swallowed, which looks like fringe crossover, with respect to the change of the inclined angle of the capillary.

Multiple beam interference model for measuring parameters of a capillary.

A multiple beam interference model based on the ray tracing method and interference theory is built to analyze the interference patterns of a capillary tube filled with a liquid. The relations between the angular widths of the interference fringes and the parameters of both the capillary and liquid are derived. Based on these relations, an approach is proposed to simultaneously determine four parameters of the capillary, i.e., the inner and outer radii of the capillary, the refractive indices of the liquid, and the wall material.