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The traditional textile degumming process produces abundant wastewater, which contains a lot of monosaccharides and oligosaccharides. It is of great economic and environmental significance to utilize these carbohydrates in high value. In this study, high performance liquid chromatography (HPLC) was used to analyze the carbohydrate components in kenaf degumming wastewater, and then the production of C-dots using the wastewater was explored. The results showed that the types and content in the degumming wastewater were monosaccharides (glucose, xylose and arabinose) and oligosaccharides (dextran, xylan and araban). The carbohydrate (mainly glucan and xylan) content in wastewater accounted for 91.16 % of the total carbohydrates weight loss in kenaf degumming process. By using hydrolysis and hydrothermal reaction on kenaf degumming wastewater, blue-green carbon dots (C-dots) with good performance were prepared and successfully applied to anti-counterfeiting printing. In particular, the as-prepared C-dots prepared from kenaf degumming wastewater with urea added (WUC-dots) showed an excitation-dependent photoluminescence (PL) spectrum and quantum yield (QY) of 2.4 % in aqueous solution. The fluorescent code exhibited a clear outline, excitation-tunable color and good stability, showing a great potential for anti-counterfeiting system., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Optical nanothermometers have attracted much attention due to their non-contact and precise measurement with high spatial resolution at the micro- and nanoscales. They can be applied in various fields such as micro-opto-electronics, photonics, and biomedical thermal and pH sensing, while most thermal sensors reported so far contain heavy metals or have low sensitivity. Herein, we demonstrate a highly sensitive ratiometric thermal sensor based on colloidal C-dots. C-dots exhibit dual emission originating from the band gap emission and surface-dominant emission, which show a different temperature-dependent photoluminescence (PL) response. Among different surface-functionalized C-dots, C-dots@OH exhibit an absolute thermal sensitivity of -0.082 °C-1, which is the highest among various types of ratiometric thermosensors, making it a very promising candidate for high-sensitivity, self-calibrated nanoscale thermometry. As a proof-of-concept, C-dots@OH were employed to monitor the intracellular temperature (32-42 °C), showing a clear trend for temperature variation in a single cell, indicating that C-dots could offer a powerful tool for a potential precise measurement of the intracellular temperature. They could also be used as thermal sensors for nano-electronic and optoelectronic devices.

Core-shell quantum dots serve as self-calibrating, ultrasensitive, multiparametric, near-infrared, and biocompatible temperature sensors. They allow temperature measurement with nanometer accuracy in the range 150-373 K, the broadest ever recorded for a nanothermometer, with sensitivities among the highest ever reported, which makes them essentially unique in the panorama of biocompatible nanothermometers with potential for in vivo biological thermal imaging and/or thermoablative therapy., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this study, we develop a reproducible and controllable microwave-assisted cation exchange approach, for the first time, to quickly synthesize high-quality, near-infrared emitting PbS/CdS core/shell quantum dots (QDs). These monodisperse QDs, emitting in the range of 1300-1600 nm, show a quantum yield as high as 57% that is ~1.4 times higher than that achieved by the same QDs prepared using conventional heating in an oil bath. To the best of our knowledge, it is the highest reproducible value reported to date for PbS-based QDs in this emission range. More importantly, the as-synthesized PbS/CdS QDs can self-assemble nearly perfectly and easily at the micrometer scale as a result of their uniform shape and narrow size distribution.

High-quality water-soluble near-infrared emitting quantum dots (QDs) are synthesized using a two-step approach for the first time. The CdS shell efficiently increases the structural stability of PbS QDs during water transfer and leads to good photostability and a significantly enhanced quantum yield as high as 30% in buffer.

Solar‐driven photoelectrochemical (PEC) reactions using colloidal quantum dots (QDs) as photoabsorbers have shown great potential for the production of clean fuels. However, the low H2 evolution rate, consistent with low values of photocurrent density, and their limited operational stability are still the main obstacles. To address these challenges, the heterostructure engineering of asymmetric capsule‐shaped CdSe/CdxZn1‐xSe QDs with broad absorption and efficient charge extraction compared to pure‐shell QDs is reported. By engineering the shell composition from pure ZnSe shells into CdxZn1‐xSe gradient shells, the electron transfer rate increased from 4.0 × 107 s−1 to 32.7 × 107 s−1. Moreover, the capsule‐shaped architecture enables more efficient spatial carrier separation, yielding a saturated current density of average of 25.4 mA cm−2 under AM 1.5 G one sun illumination. This value is the highest ever observed for QDs‐based devices and comparable to the best‐known Si‐based devices, perovskite‐based devices, and metal oxide‐based devices. Furthermore, PEC devices based on heterostructured QDs maintained 96% of the initial current density after 2 h and 82% after 10 h under continuous illumination, respectively. The results represent a breakthrough in hydrogen production using heterostructured asymmetric QDs. [ABSTRACT FROM AUTHOR]

Colloidal carbon dots (C‐dots) are considered as promising heavy‐metal‐free materials to achieve room‐temperature phosphorescence (RTP) properties for promising applications, such as photoelectronic devices, information encryption, and bio‐imaging. However, most of the current obtained RTP C‐dots have a short lifetime with a relatively low quantum yield (QY). In this work, the C‐dots large‐scale synthesized via a vacuum heating approach have multiple RTP emissions (blue, green, and yellow), a long RTP lifetime of as high as 1.92 s, and a high QY of 34.4% by selecting different types of precursors, which is superior to most of reported RTP C‐dots. The multiple atoms doping and strong bonding between neighbored C‐dots promoted by vacuum heating contributes to the excellent RTP properties. As a proof‐of‐concept, the as‐obtained RTP C‐dots are used as optical ink for flexible security codes, exhibiting a bright shape with a lifetime of 1.37 s. This work offers an efficient approach for producing large‐scale high‐quality RTP C‐dots, which can be applied to anti‐counterfeiting and information encryption systems. [ABSTRACT FROM AUTHOR]

Colloidal indium phosphide (InP) quantum dots (QDs) have attracted a great attention for their excellent optical properties, and they are a promising candidate for potential applications in optoelectronic devices, such as photocatalysis, light emitting diodes, and bioimaging. However, their use for luminescent solar concentrators (LSCs) has been limited owing to their low optical efficiency, which is because of the energy loss due to the strong overlap between their emission and absorption spectra. Here, we synthesized pyramidal InP/ZnSe QDs based on aminophosphine as the phosphorus precursor by adding hydrofluoric acid to remove the oxides on the InP core surface before the growth of a ZnSe shell. Through researching the exciton dynamic of InP/ZnSe QDs with different shell thicknesses, we found that a thick shell can stabilize the 1Pe energy state of the InP core, thus decreasing the spectral overlap in the overall QDs. As a proof of concept, we demonstrated a highly efficient LSC based on "giant" InP/ZnSe QDs, which exhibited an external optical efficiency of 2.5% and a power conversion efficiency of 2% (5 × 5 × 0.5 cm3) upon simulated sunlight illumination (100 mW/cm2), which is among the best reported LSCs based on InP QDs. Pyramidal "giant" InP/ZnSe QDs hold great potential for the breakthrough development in the field of eco-friendly QD-based LSCs. [ABSTRACT FROM AUTHOR]

Large scale solar‐driven hydrogen production is a crucial step toward decarbonizing society. However, the solar‐to‐hydrogen (STH) conversion efficiency, long‐term stability, and cost‐effectiveness in hydrogen evolution reaction (HER) still need to be improved. Herein, an efficient approach is demonstrated to produce low‐dimensional Pt/graphene‐carbon nanofibers (CNFs)‐based heterostructures for bias‐free, highly efficient, and durable HER. Carbon dots are used as efficient building blocks for the in situ formation of graphene along the CNFs surface. The presence of graphene enhances the electronic conductivity of CNFs to ≈3013.5 S m−1 and simultaneously supports the uniform Pt clusters growth and efficient electron transport during HER. The electrode with a low Pt loading amount (3.4 µg cm−2) exhibits a remarkable mass activity of HER in both acidic and alkaline media, which is significantly better than that of commercial Pt/C (31 µg cm−2 of Pt loading). In addition, using a luminescent solar concentrator‐coupled solar cell to provide voltage, the bias‐free water splitting system exhibits an STH efficiency of 0.22% upon one‐sun illumination. These results are promising toward using low‐dimensional heterostructured catalysts for future energy storage and conversion applications. [ABSTRACT FROM AUTHOR]

Solar‐driven photoelectrochemical (PEC) hydrogen evolution is a promising and sustainable approach to convert solar energy into a fuel that can be stored. Semiconductor quantum dots (QDs) are increasingly used in PEC devices due to their broad composition/size/shape tunable absorption spectrum (from ultraviolet to near‐infrared, with significant overlap with the solar spectrum). Despite significant efforts and recent progress, several major challenges remain unresolved in this fast‐developing field. Here, the latest progress in tailoring the materials, structure, and performance of QDs‐based PEC H2 generation, including photoanodes, photocathodes, and tandem PEC systems, is summarized. In particular, recent strategies developed for PEC H2 generation are critically analyzed. Specific features of QDs (e.g., size/shape/composition‐tunable absorption band edge arising from quantum confinement, ease of fabrication through chemical approaches, and multiple exciton generation), charge generation, and charge transfer of photoelectrodes and their implications on the performance of PEC devices are discussed. Future challenges and opportunities working, toward high‐efficiency and stable QDs‐based PEC applications are discussed in the conclusion. [ABSTRACT FROM AUTHOR]

Here, a facile approach to enhance the performance of solar‐driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2–Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSexS1−x)5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm−2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm−2), which is ≈26% higher than the control device. The in‐depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2–Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot‐electron injection from Au NPs into CNTs and TiO2; ii) near‐field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2–Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies. [ABSTRACT FROM AUTHOR]

Accurate temperature measurements with a high spatial resolution for application in the biomedical fields demand novel nanosized thermometers with new advanced properties. Here, a water dispersible ratiometric temperature sensor is fabricated by encapsulating in silica nanoparticles, organic capped PbS@CdS@CdS "giant" quantum dots (GQDs), characterized by dual emission in the visible and near infrared spectral range, already assessed as efficient fluorescent nanothermometers. The chemical stability, easy surface functionalization, limited toxicity and transparency of the silica coating represent advantageous features for the realization of a nanoscale heterostructure suitable for temperature sensing. However, the strong dependence of the optical properties on the morphology of the final core–shell nanoparticle requires an accurate control of the encapsulation process. We carried out a systematic investigation of the synthetic conditions to achieve, by the microemulsion method, uniform and single core silica coated GQD (GQD@SiO2) nanoparticles and subsequently recorded temperature-dependent fluorescent spectra in the 281-313 K temperature range, suited for biological systems. The ratiometric response—the ratio between the two integrated PbS and CdS emission bands—is found to monotonically decrease with the temperature, showing a sensitivity comparable to bare GQDs, and thus confirming the effectiveness of the functionalization strategy and the potential of GQD@SiO2 in future biomedical applications. [ABSTRACT FROM AUTHOR]

Semiconductor nanocrystals, the so‐called quantum dots (QDs), exhibit versatile optical and electrical properties. However, QDs possess high density of surface defects/traps due to the high surface‐to‐volume ratio, which act as nonradiative carrier recombination centers within the QDs, thereby deteriorating the overall solar cell performance. The surface passivation of QDs through the growth of an outer shell of different materials/compositions called "core/shell QDs" has proven to be an effective approach to reduce the surface defects and confinement potential, which can enable the broadening of the absorption spectrum, accelerate the carrier transfer, and reduce exciton recombination loss. Here, the recent research developments in the tailoring of the structure of core/shell QDs to tune exciton dynamics so as to improve solar cell performance are summarized. The role of band alignment of core and shell materials, core size, shell thickness/compositions, and interface engineering of core/thick shell called "giant" QDs on electron–hole spatial separation, carrier transport, and confinement potential, before and after grafting on the carrier scavengers (semiconductor/electrolyte), is described. Then, the solar cell performance based on core/shell QDs is introduced. Finally, an outlook for the rational design of core/shell QDs is provided, which can further promote the development of high‐efficiency and stable QD sensitized solar cells. [ABSTRACT FROM AUTHOR]

Abstract Colloidal semiconductor quantum dots (QDs) have attracted a great attention for their potential applications in optoelectronic devices, such as water splitting, luminescent solar concentrators, and solar cells, because of their size/shape/composition-dependent optoelectronic properties. However, the fast electron-hole (e-h) recombination and slow charge separation of QDs limit their applications as light absorbers in high-efficiency optoelectronic devices. Here, we synthesized thick-shell CdSe/CdSe x S 1-x /CdS QDs with pyramidal shape, which exhibit a quantum yield of ~ 15%, with a long radiative lifetime up to ~ 100 ns due to the spatial separation of the e/h wavefunction and significantly broadened light absorption toward the 500–700 nm range, compared to CdSe/CdS unalloyed QDs. As a proof-of-concept, the pyramidal QDs are applied as light absorbers in a photoelectrochemical (PEC) system, leading to a saturated photocurrent density of ~ 12 mA/cm2 (with a H 2 generation rate of 90 mL cm−2 day−1), which is a record for thick-shell QD-based photoelectrodes in PEC hydrogen generation. Core/thick-shell QDs hold great potential for breakthrough developments in the field of QD-based optoelectronic devices. Graphical abstract fx1 Highlights • First synthesis of quasi-pyramidal thick-shell CdSe/CdSe x S 1-x /CdS QDs for PEC H 2 production. • Broad absorption spectrum obtained (range 300–670 nm), much wider than that of CdSe/CdS QDs with pyramidal or spherical shape (< 500 nm). • Pyramidal thick-shell QDs exhibit efficient electron leakage to the shell range (results on lifetime measurement and theoretical simulations). • Saturated photocurrent density as high as ~ 12 mA/cm2. This value is a record for PEC devices based on thick-shell "giant" QDs. [ABSTRACT FROM AUTHOR]

Luminescent solar concentrator (LSC) can serve as large-area sunlight collectors, suitable for applications in building-integrated high-efficiency and low-cost photovoltaics. Inorganic perovskite quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs, due to their high quantum yields (close to 100%), possibility of tuning size and chemical composition and broad absorption spectrum and high absorption coefficient. However, despite their great potential for technological development, LSCs fabricated using colloidal perovskite QDs still face major challenges such as low optical efficiency and limited long-term stability. Here we report a large-area (~ 100 cm 2 ) tandem LSC based on nearly reabsorption-free carbon dots (C-dots) and inorganic mixed-halide perovskite QDs spectrally-tuned for optimal solar-spectrum splitting. The as-fabricated semi-transparent device, without involving any complicated processes, exhibits an external optical efficiency of ~ 3% under sunlight illumination (100 mW/cm 2 ), which represents a 27% enhancement in efficiency over single layer LSCs based on CsPb(Br x I 1-x ) 3 QDs and 117% over CsPb(Cl x Br 1-x ) 3 QDs. Our work shows that the addition of C-dots can dramatically enhance the long-term durability of LSC devices based on perovskite QDs due to their excellent photostability and simultaneous absorption of ultraviolet light. [ABSTRACT FROM AUTHOR]

Abstract: Colloidal heterostructured quantum dots (QDs) are promising candidates for next‐generation optoelectronic devices. In particular, “giant” core/shell QDs (g‐QDs) can be engineered to exhibit outstanding optical properties and high chemical/photostability for the fabrication of high‐performance optoelectronic devices. Here, the synthesis of heterostructured CuInSexS2−x (CISeS)/CdSeS/CdS g‐QDs with pyramidal shape by using a facile two‐step method is reported. The CdSeS/CdS shell is demonstrated to have a pure zinc blend phase other than typical wurtzite phase. The as‐obtained heterostructured g‐QDs exhibit near‐infrared photoluminescence (PL) emission (≈830 nm) and very long PL lifetime (in the microsecond range). The pyramidal g‐QDs exhibit a quasi‐type II band structure with spatial separation of electron–hole wave function, suggesting an efficient exciton extraction and transport, which is consistent with theoretical calculations. These heterostructured g‐QDs are used as light harvesters to fabricate a photoelectrochemical cell, exhibiting a saturated photocurrent density as high as ≈5.5 mA cm−2 and good stability under 1 sun illumination (AM 1.5 G, 100 mW cm−2). These results are an important step toward using heterostructured pyramidal g‐QDs for prospective applications in solar technologies. [ABSTRACT FROM AUTHOR]

Abstract: “Giant” core/shell quantum dots (g‐QDs) are a promising class of materials for future optoelectronic technologies due to their superior chemical‐ and photostability compared to bare QDs and core/thin shell QDs. However, inadequate light absorption in the visible and near‐infrared (NIR) region and frequent use of toxic heavy metals (e.g., Cd and Pb) are still major challenges for most g‐QDs (e.g., CdSe/CdS) synthesized to date. The synthesis of NIR, heavy metal‐free, Zn‐treated spherical CuInSe2/CuInS2 g‐QDs is reported using the sequential cation exchange method. These g‐QDs exhibit tunable NIR optical absorption and photoluminescence (PL) properties. Transient fluorescence spectroscopy shows prolonged lifetime with increasing shell thickness, indicating the formation of quasi type‐II band alignment, which is further confirmed by simulations. As a proof‐of‐concept, as‐synthesized g‐QDs are used to sensitize TiO2 as a photoanode in a photoelectrochemical (PEC) cell, demonstrating an efficient and stable PEC system. These results pave the way toward synthesizing NIR heavy metal‐free g‐QDs, which are very promising components of future optoelectronic technologies. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (QDs) are widely studied due to their promising optoelectronic properties. This study explores the application of specially designed and synthesized "giant" core/shell CdSe/(CdS)x QDs with variable CdS shell thickness, while keeping the core size at 1.65 nm, as a highly efficient and stable light harvester for QD sensitized solar cells (QDSCs). The comparative study demonstrates that the photovoltaic performance of QDSCs can be significantly enhanced by optimizing the CdS shell thickness. The highest photoconversion efficiency (PCE) of 3.01% is obtained at optimum CdS shell thickness ≈1.96 nm. To further improve the PCE and fully highlight the effect of core/shell QDs interface engineering, a CdSexS1-x interfacial alloyed layer is introduced between CdSe core and CdS shell. The resulting alloyed CdSe/(CdSexS1-x)5/(CdS)1 core/shell QD-based QDSCs yield a maximum PCE of 6.86%, thanks to favorable stepwise electronic band alignment and improved electron transfer rate with the incorporation of CdSexS1-x interfacial layer with respect to CdSe/(CdS)6 core/shell. In addition, QDSCs based on "giant" core/ CdS-shell or alloyed core/shell QDs exhibit excellent long-term stability with respect to bare CdSe-based QDSCs. The giant core/shell QDs interface engineering methodology offers a new path to improve PCE and the long-term stability of liquid junction QDSCs. [ABSTRACT FROM AUTHOR]

Luminescent solar concentrators (LSCs) are considered a promising technology to reduce the cost of electricity by decreasing the use of expensive photovoltaic materials, such as single-crystal silicon. In addition, LSCs are suitable for applications in building-integrated photovoltaics. Inorganic perovskite quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs, due to their excellent optical properties including size/chemical-composition dependent absorption/emission spectrum, high absorption coefficient, high quantum yield and good stability. However, due to the large overlap between their absorption and emission spectra, it is still very challenging to fabricate large-area high-efficiency LSCs using perovskite QDs. Here we report the synthesis of mixed-halide perovskite CsPb(Br x I 1−x ) 3 QDs with small overlap of absorption and emission spectra, high quantum yield (over 60%) and absorption spectrum ranging from 300 to 650 nm. We use these QDs to build semi-transparent large-area LSCs that exhibit an external optical efficiency of 2% with a geometrical gain factor of 45 (9 cm in length). To date, these represent the brightest and most efficient solution-processed perovskite QDs based LSCs compared to LSCs based on perovskite thin films. The LSCs exhibit long term air stability without any noticeable variation in photoluminescence and lifetime under 4 W UV light illumination for over four hours. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) hydrogen generation based on colloidal quantum dots (QDs) is very promising because of its high solar energy to fuel conversion efficiency and low fabrication costs. However, its commercial development is hindered by various challenges, including the widespread use of toxic heavy metal–based QDs as sensitizers. We report an environmentally friendly, high efficiency PEC device in which the photoanode consists of a mesoporous TiO 2 film sensitized with heavy metal-free, near-infrared (NIR) colloidal CuInSe x S 2−x (CISeS) QDs. To reduce surface-related traps, we grew an ultrathin ZnS shell on the CISeS core QDs by cation exchange. The PEC cell based on this core/shell CISeS/ZnS QDs exhibits suppressed charge recombination and a saturated photocurrent density of ~5.3 mA/cm 2 under one sun illumination (AM 1.5 G, 100 mW/cm 2 ). In addition, the as-prepared PEC device shows an outstanding stability, exhibiting a drop of only 23% after 9 h illumination. The success in using such core/shell CISeS/ZnS QDs paves the way to realize environment-friendly, high efficiency and cost-effective PEC devices for hydrogen production. [ABSTRACT FROM AUTHOR]

The fabrication of a low reabsorption emission loss, high efficient luminescent solar concentrator (LSC) is demonstrated by embedding near infrared (NIR) core/shell quantum dots (QDs) in a polymer matrix. An engineered Stokes shift in NIR core/shell PbS/CdS QDs is achieved via a cation exchange approach by varying the core size and shell thickness through the refined reaction parameters such as reaction time, temperature, precursor molar ratio, etc. The as-synthesized core/shell QDs with high quantum yield (QY) and excellent chemical/photostability exhibit a large Stokes shift with respect to the bare PbS QDs due to the strong core-to-shell electrons leakage. The large-area planar LSC based on core/shell QDs exhibits the highest value (6.1% with a geometric factor of 10) for optical efficiency compared to the bare NIR QD-based LSCs and other reported NIR QD-based LSCs. The suppression of emission loss and the broad absorption of PbS/CdS QDs offer a promising pathway to integrate LSCs and photovoltaic devices with good spectral matching, indicating that the proposed core/shell QDs are strong candidates for fabricating high efficiency semi-transparent large-area LSCs. [ABSTRACT FROM AUTHOR]

Quantum Dots: Quantum Dots-Based Photoelectrochemical Hydrogen Evolution from Water Splitting (Adv. In article 2003233, Haiguang Zhao, Federico Rosei and co-workers summarize the latest progress in QDs-based PEC H SB 2 sb generation, including photoanodes, photocathodes and tandem systems. Keywords: hydrogen; photoelectrochemical water splitting; quantum dots; solar technology EN hydrogen photoelectrochemical water splitting quantum dots solar technology 1 1 1 03/27/21 20210325 NES 210325 Quantum dots (QDs) are increasingly used in photoelectrochemical (PEC) devices due to their broad composition/size/shape tunable absorption spectrum. [Extracted from the article]

High-quality water-soluble near-infrared emitting quantum dots (QDs) are synthesized using a two-step approach for the first time. The CdS shell efficiently increases the structural stability of PbS QDs during water transfer and leads to good photostability and a significantly enhanced quantum yield as high as 30% in buffer. [ABSTRACT FROM AUTHOR]

Quantum Dots Solar Cells: Core/Shell Quantum Dots Solar Cells (Adv. Funct. Keywords: carrier dynamics; core/shell quantum dots; interface engineering; quantum dot sensitized solar cells EN carrier dynamics core/shell quantum dots interface engineering quantum dot sensitized solar cells 1 1 1 03/28/20 20200324 NES 200324 In article number 1908762, Haiguang Zhao, Zhiming M. Wang, Federico Rosei, and Gurpreet Singh Selopal report on colloidal core/shell quantum dots (QDs) that exhibit promising optical and electrical properties. Carrier dynamics, core/shell quantum dots, interface engineering, quantum dot sensitized solar cells. [Extracted from the article]

Group II–VI quantum dots (QDs) possess tunable electrical and optical properties that make them very attractive for high‐tech applications and power generation. The effects of proton irradiation on both the structural and physical properties of "giant" CdSe/CdS core–shell QDs (g‐CS QDs) are investigated. These experiments shed light on photoelectron delocalization in g‐CS QDs, where current linkages and strong variations in optical emission result from the spatial extension of the photoelectron wavefunctions over the conduction bands of CdSe and CdS. Monte Carlo simulations of ion–matter interactions show that the damaging rates can be set from the energy of impinging protons to promote the formation of structural defects in the core or shell. The formation of nanocavities is demonstrated after irradiation doses higher than ≈1017 H+ cm−2, while a continuous decrease in luminescence intensity is observed for increasing proton fluencies. This feature is accompanied by a concomitant lifetime decrease marking the rise of nonradiative phenomena and the occurrence of greater photocarrier transfers between CdS and CdSe. Current‐to‐voltage characterizations evidence that proton implantation can be implemented to enhance the photocurrent generation in g‐CS QDs. This increase is attributed to the delocalization of photoelectrons in the CdS shell, whose improvement is found to promote electron–hole pair separation. [ABSTRACT FROM AUTHOR]

The fabrication of a low reabsorption emission loss, highly efficient luminescent solar concentrator (LSC), based on near infrared core/shell quantum dots embedded in a polymer matrix is demonstrated in article number 1501913, by Haiguang Zhao, Alberto Vomiero, Federico Rosei, and co‐workers. The semi‐transparent LSC exhibits an optical efficiency of 6.1% for a geometric factor G equal to 10, which is unprecedented for planar LSCs based on near infrared quantum dots. [ABSTRACT FROM AUTHOR]

• A triple-layer LSC was fabricated, with an external optical efficiency of 9.1 %, and a PCE of 6.0 %. • The blue-, green- and orange- emitting C-dots have a quantum yield of 90 %, 73 %, and 72 %. • The multilayer LSCs have high CRI above 80 and AVT above 70 %, suitable for efficient BIPVs. Compared to the silicon-based photovoltaics, large-area luminescent solar concentrators (LSCs) can be used as smart PV window for building-integrated photovoltaics (BIPVs). However, because of the low quantum yield of the fluorophores, and reabsorption energy loss, the current obtained large-area LSCs have low optical efficiency. Herein, we demonstrated highly efficient and semitransparent multilayer LSCs based on three types of carbon quantum dots (C-dots). The blue and green C-dots were synthesized using vacuum heating approach and the orange C-dots were synthesized using solvothermal approach. The as-prepared B-, G- and O-C-dots have the QYs of 90 %, 73 % and 72 %, respectively, with large Stokes shift (0.37–0.73 eV). By optimizing the concentration of the C-dots in each layer, the best LSC (100 cm2) with multilayer structure exhibited an external optical efficiency of 9.1 %, and a power conversion efficiency (PCE) of 6.0 %, which are higher than that of most of reported LSCs. The simulations indicate that optimized multilayer LSCs could have a theoretical external optical efficiency over 12 % for 1 m2 devices. Besides high optical efficiency, the multilayer LSCs also have high Color Rendering Index (above 80) and high average visible transmission (above 70 %), which make the as-prepared LSCs suitable for potential commercial BIPVs. [ABSTRACT FROM AUTHOR]

• A facile strategy to align graphene oxide (GO) within 1D cobalt-based nanohybrids (CoNHs). • Addition of GO remarkably enhances the charge transfer within the CoNHs. • GO/CoNHs display outstanding long-term stability (for over 42 h) in alkaline media. • 1D CoNHs (Co 3 O 4) rebuild and regenerate in situ leading to 2D nanosheets (Co 3 S 4 and CoS 2). • GO/CoNHs demonstrate potential as electrocatalysts in solar-driven hydrogen (H 2) generation. Low-cost nanostructured hybrid materials and the optimization of their structural design present an opportunity to achieve high performance and stable renewable energy devices. Here we used electrospinning to homogeneously embed graphene oxide (GO) nanosheets within the one-dimensional structure of cobalt-based nanohybrids (CoNHs). In particular, we focus on the performance of these nanohybrids in Na 2 S/Na 2 SO 3 aqueous electrolyte (pH = 13) due to its wide application in photocatalytic and photoelectrochemical (PEC) devices. We demonstrate that the addition of GO can remarkably reduce the charge transfer resistance from 4.4 Ω to 2.5 Ω for the 0 wt% GO/CoNHs and the 12 wt% GO/CoNHs, respectively. Furthermore, the CoNHs display outstanding electrochemical long-term stability, as the overpotential required to keep J = −10 mA cm−2 is invariable for over 42 h. The structural characterization of the nanohybrids indicates that during continuous operation, the CoNHs rebuild and regenerate in situ leading to the formation of two-dimensional nanostructures comprising a mixture of cobalt chalcogenides (Co 3 S 4 and CoS 2). The integration of the CoNHs in a quantum-dot based PEC cell and an alkaline electrolyzer (1 M KOH) demonstrates the versatility and viability of these alternative electrodes toward active and solar-driven fuel generation. [ABSTRACT FROM AUTHOR]

Abstract Colloidal quantum dots (QDs) have attracted a lot of attention due to their unique optoelectronic properties. They have been widely used as building block materials for solar technologies such as solar cell, and photoelectrochemical (PEC) water splitting. Hydrogen generation by using QDs as photocatalysts has emerged a promising application in PEC devices. However, it is still very challenging to obtain high-efficiency PEC devices due to the limited absorption wavelength of QDs and the existence of surface traps which prohibit the efficient charge transfer. In this work, we synthesized ternary CdSe x Te 1-x /CdS (CdSeTe/CdS) "giant" QDs to extend the light absorption to near infrared, matched well with Sun's spectrum. The as-synthesized CdSeTe/CdS "giant" QDs exhibit quasi-type II band alignment as confirmed by its long lifetime and red-shifted emission peak compared with bare CdSeTe QDs. The wide absorption range of "giant" core/shell QDs and their long lifetime can improve the efficient absorption of Sun's spectrum and charge transfer. As a proof-of-concept, a PEC device using QDs sensitized TiO 2 mesoporous thin film as a photoanode was used for hydrogen production. The corresponding photocurrent density was increased to 3.0 mA/cm2 with the introduction of CdS shell, which is 1.5 times higher than the PEC device using CdSeTe QDs. This study indicates that ternary or polynary alloyed core/shell QDs can be used as promising optoelectronic materials for applications of PEC devices. Highlights • Ternary alloyed CdSeTe and CdSeTe/CdS QDs were explored for PEC hydrogen generation. • The CdSeTe/CdS core/shell QDs exhibit a twelve-fold extension of lifetime. • 1.5 times H 2 generation rate was obtained for core-shell QDs compared to bare QDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • We demonstrated a porous Co 3 O 4 / C-dots nanofibers for efficient HER. • The hybrid nanofibers-based electrode achieved 10 mA cm−2 at a low overpotential of 383 mV, much lower than that of Co 3 O 4 (758 mV). • The presence of C-dots not only decreases the diameter of the nanofiber, but also improves the charge transfer. • Co 3 S 4 /C-dots nanofibers were synthesized by one-step hydrothermal method with Co 3 O 4 / C-dots nanofibers, and showed better HER performance (280.2 mV). Hydrogen is increasingly needed as a clean energy source with high energy density. Hydrogen evolution reaction (HER) via electrocatalysis is a viable way to produce clean hydrogen. The key to achieving active HER is to select highly-active electrocatalysts. Although Pt-based noble metal catalysts have excellent performance, they are expensive and earth-abundant. Compared to noble metals, cobalt chalcogenide has been used for efficient HER. Here, we first demonstrated a porous material based on C-dots/cobalt chalcogenide nanofibers as an effective electrocatalyst for HER. Co 3 O 4 /10 wt% C-dots nanofibers-based electrode reached an overpotential of 383 mV at the current density of 10 mA·cm−2 with Tafel slope of 93.4 mV·dec−1 in 1 M KOH, which is much better than bare Co 3 O 4 (758 mV at 10 mA·cm−2, Tafel slope is 111.3 mV·dec−1). In addition to the excellent HER performance, the Co 3 O 4 /C-dots nanofibers performed very well in terms of stability after a 10-hour operation, and the overpotential was even reduced by 6.7%. With the further sulphuration, the Co 3 S 4 /C-dots nanofibers exhibited an overpotential of 280.2 mV at the current density of 10 mA·cm−2. This work indicates that the C-dots can be used as an efficient additive for cobalt chalcogenide based electrocatalysts. [ABSTRACT FROM AUTHOR]

• Eco-friendly CuGaAlS/ZnS core/shell QDs were successfully synthesized. • Optical properties of QDs can be tuned by varying the copper contents. • The optimized QDs show a high PLQY of 91% with a large Stokes-shift. • High-performance and large-area QDs-based LSC device is fabricated. Luminescent solar concentrators (LSCs) fabricated using colloidal quantum dots (QDs) are considered as promising cost-effective solar collectors for future building-integrated photovoltaics (BIPV). Nevertheless, the solar-to-electricity conversion efficiency of the LSCs is commonly low due to limited quantum efficiency and large reabsorption loss of QDs. In addition, most of the efficient LSCs contain heavy metal-based QDs, limiting their potential commercial applications. Herein, we demonstrate a novel type of eco-friendly CuGaAlS/ZnS (CGAS/ZnS) core/shell QDs with efficient surface passivation and manipulated their optical properties by varying the copper contents, which effectively regulates the intrinsic band structure and radiative recombination dynamics. As a result, the optimal Cu-deficient CGAS/ZnS core/shell QDs exhibit the highest photoluminescence quantum yield (PLQY) of ∼ 91 % and large Stokes shift (∼0.81 eV). The prepared QDs were applied as emitters and integrated in polymer matrix to fabricate LSCs (10 × 10 × 0.15 cm3), delivering an unprecedented power conversion efficiency (PCE) of 4.29 % under standard one sun AM 1.5G illumination (100 mW cm−2). Our results imply that tuning the components of multinary environment-friendly core/shell QDs endows the feasibility to realize low-cost and high-efficiency BIPV applications. [ABSTRACT FROM AUTHOR]

• Hybrid ligands exchange replaced ~75% of organic OA ligands. • PEC cells with a hybrid ligand exchange yield two times higher current density. • Hybrid ligand exchange offers reduced charge transfer resistance/prolonged lifetime. Surface ligands facilitate the high dispersibility of colloidal quantum dots (QDs) during synthesis and storage, and also play a key role in passivating surface traps. The most commonly used ligands [oleic acid (OA) or oleylamine (OLA)] are insulating long organic linkers, which prevent efficient charge transfer between QDs and exhibit limited surface passivation, thus significantly reducing the overall performance of QDs based optoelectronic devices. Here we develop a solid-state ligands exchange process for PbS/CdS QDs sensitized TiO 2 photoanode with hybrid inorganic ligands (I− and SCN−) to replace the original insulating OA ligands and passivate the surface traps. The hybrid surface passivation of PbS/CdS QDs removes ~75% of insulating OA ligands. The saturated photocurrent density of the photoelectrochemical (PEC) cells improves significantly through the hybrid ligand exchange process, reaching a value of 4.0 mA cm−2 which is more than two times higher compared to the control PEC cells. In addition, the long-term stability of PEC cells is better for the hybrid ligand exchange process (only 15% loss of its initial photocurrent density) than the control PEC cells (38% loss). Our results indicate that hybrid ligands engineering is a promising pathway to achieve high performance and stable PEC cells for hydrogen generation. [ABSTRACT FROM AUTHOR]

The counter electrode (CE) plays a significant role in determining the overall performance and long-term stability of quantum dots (QDs) sensitized solar cells (QDSCs) by collecting the electrons from the external circuit and catalyzing the regeneration of the oxidized electrolyte. In this work, we report a simple, low cost and large area scalable spray deposition approach to fabricate nanostructured Cu 2 S CE on a carbon fiber paper (CP). The QDSCs were assembled with optimized spray assisted nanostructured Cu 2 S/CP CEs, and yield a photoconversion efficiency (PCE) of 5.06%, which is 28% higher than QDSCs based on Cu 2 S/Brass CEs. The PCE can be further boosted to 5.89% upon optimization of the photoanode structure. In addition, QDSCs with Cu 2 S/CP CEs exhibit better long-term stability than QDSCs with Cu 2 S/Brass CE. This excellent performance and satisfactory long-term stability of QDSCs with Cu 2 S/CP CEs is mainly attributed to the synergistic effect of excellent conductivity of CP and high and stable catalytic activity of nanostructured Cu 2 S, which is confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Thus, our results define a cost-effective and large area scalable approach to fabricate highly efficient and stable CEs, which is an important step toward the fabrication of solar driven optoelectronic devices. Image 1 • The spray deposition approach was used to fabricate efficient and stable Cu 2 S/CP CE. • Cu 2 S/CP CEs offer low series resistance and high catalytic activity. • QDSC based on Cu 2 S/CP CEs yield a 28% higher PCE than the brass CEs. • A PCE of 5.89% can be obtained upon the optimization of the photoanode structure. [ABSTRACT FROM AUTHOR]