Advanced energy conversion and storage (ECS) devices (including fuel cells, photoelectrochemical water splitting cells, solar cells, Li-ion batteries and supercapacitors) are expected to play a major role in the development of sustainable technologies that alleviate the energy and environmental challenges we are currently facing. The successful utilization of ECS devices depends critically on synthesizing new nanomaterials with merits of low cost, high efficiency, and outstanding properties. Recent progress has demonstrated that nanostructured metal chalcogenides (MCs) are very promising candidates for efficient ECS systems based on their unique physical and chemical properties, such as conductivity, mechanical and thermal stability and cyclability. In this review, we aim to provide a summary on the liquid-phase synthesis, modifications, and energy-related applications of nanostructured metal chalcogenide (MC) materials. The liquid-phase syntheses of various MC nanomaterials are primarily categorized with the preparation method (mainly 15 kinds of methods). To obtain optimized, enhanced or even new properties, the nanostructured MC materials can be modified by other functional nanomaterials such as carbon-based materials, noble metals, metal oxides, or MCs themselves. Thus, this review will then be focused on the recent strategies used to realize the modifications of MC nanomaterials. After that, the ECS applications of the MC/modified-MC nanomaterials have been systematically summarized based on a great number of successful cases. Moreover, remarks on the challenges and perspectives for future MC research are proposed (403 references).

Nanostructured metal chalcogenides: synthesis, modification, and applications in energy conversion and storage devices

The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminesce...

Spectroscopic and Device Aspects of Nanocrystal Quantum Dots

We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III–V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors’ view on the perspectives in this field is given.

Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials.

The chemistry, material processing and fundamental understanding of colloidal semiconductor nanocrystals (quantum dots) are advancing at an astounding rate, bringing the prospects of widespread commercialization of these novel and exciting materials ever closer. Interest in narrow bandgap nanocrystals in particular has intensified in recent years, and the results of research worldwide point to the realistic prospects of applications for these materials in solar cells, infrared optoelectronics (e.g. lasers, optical modulators, photodetectors and photoimaging devices), low cost/large format microelectronics, and in biological imaging and biosensor systems to name only some technologies. Improvements in fundamental understanding and material quality are built on a vast body of experience spread over many different methods of colloidal synthetic growth, each with their own strengths and weaknesses for different materials and sometimes with regard to particular applications. The nanocrystal growth expertise is matched by a rapidly expanding, and highly interdisciplinary, understanding of how best to assemble these materials into films or hybrid composites and thereby into useful devices, and again there are many different strategies that can be adopted. In this review we have attempted to survey and compare the recent work on colloidal synthesis, film and nanocrystal composite material fabrication, concentrating on narrow bandgap chalcogenide materials and some of their topical applications in the solar energy and biological fields. Since these applications are attracting rising interest across a wide range of disciplines, from the biological sciences, device engineering, and materials processing fields as well as the physics and synthetic chemistry communities, we have endeavoured to make the review of these narrow bandgap nanomaterials both comprehensive and accessible to newcomers to the area.

Narrow bandgap colloidal metal chalcogenide quantum dots: synthetic methods, heterostructures, assemblies, electronic and infrared optical properties

We dope CdSe nanocrystals with Ag impurities and investigate their optical and electrical properties. Doping leads not only to dramatic changes but surprising complexity. The addition of just a few Ag atoms per nanocrystal causes a large enhancement in the fluorescence, reaching efficiencies comparable to core–shell nanocrystals. While Ag was expected to be a substitutional acceptor, nonmonotonic trends in the fluorescence and Fermi level suggest that Ag changes from an interstitial (n-type) to a substitutional (p-type) impurity with increased doping.

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Electronic Impurity Doping in CdSe Nanocrystals

A general, one-pot, single-step method for producing colloidal silver chalcogenide (Ag2E; E = Se, S, Te) nanocrystals is presented, with an emphasis on Ag2Se. The method avoids exotic chemicals, high temperatures, and high pressures and requires only a few minutes of reaction time. While Ag2S and Ag2Te are formed in their low-temperature monoclinic phases, Ag2Se is obtained in a metastable tetragonal phase not observed in the bulk.

Facile synthesis of silver chalcogenide (Ag2E; E=Se, S, Te) semiconductor nanocrystals.

SiC nanostructured coatings were deposited using a novel synthesis process combining chemical vapor deposition (CVD) with nanoparticle impaction. Indentation moduli (∼370 GPa) were similar to and hardnesses (∼39 GPa) exceeded the best commercially grown CVD films. Furthermore, film fracture toughness (∼ 6 MPa m 1/2 ) showed significant improvement to reported values in the literature. The nanoparticles were synthesized by injecting chemical reactants into a thermal plasma that undergoes a rapid expansion through a converging nozzle, resulting in a gas-phase nucleation. This purposefully runs counter to design criteria for CVD, where the reactant concentration is kept low to avoid gas-phase nucleation and a disordering of film growth. By limiting the residence time, the average particle size can be kept under 20 nm. However, these nanoparticle films suffer greatly from porosity. In the present paper, an increase in substrate temperature is used to enhance the amount of growth due to chemical vapor deposition. Particle formation was confirmed with in-situ particle size distribution measurements. The relative amount of chemical vapor to particle contributions to the film growth was investigated through observation of preferred growth orientation and microstructural characteristics. In addition, improvements in hardness and fracture toughness are presented and explained in terms of observed structural changes.

Nanostructured SiC by chemical vapor deposition and nanoparticle impaction

We report the use of aerodynamic lenses to deposit micropatterns of colloidal semiconductor nanocrystals (or quantum dots). CdSe and CdSe/ZnS core/shell nanocrystals, with core diameters of 3.5–5 nm, were dispersed in hexane and then nebulized to generate agglomerates a few tens of nm in diameter, consisting of hundreds of nanocrystals. These agglomerates were then focused aerodynamically by a lens system. Microscale towers, lines, and patterns were deposited on thin sapphire plates and silicon wafers. The heights and widths of the deposits were adjustable by varying the experimental parameters. Line widths below 10 μm at full-width half-maximum are demonstrated. Upon exposure to near-UV illumination, these deposits exhibited robust fluorescence in the visible, with the color depending on the diameter of the individual nanocrystal cores. A red shift of the photoluminescence peaks from the nanocrystal dispersion to the glassy solid deposits was also observed, which confirmed that the deposits consist of cl...

Micropattern deposition of colloidal semiconductor nanocrystals by aerodynamic focusing

Structurally well-defined and nearly monodisperse colloidal Ag2Se nanocrystals are synthesized from tri-n-octylphosphine solutions containing AgNO3, Se, oleic acid, 1-octadecylamine, and 1-octadecene (150 °C, about 5 min).

Facile Synthesis of Silver Chalcogenide (Ag2E; E: Se, S, Te) Semiconductor Nanocrystals.

We use aerosol techniques to investigate the cohesive and granular properties of solids composed of colloidal semiconductor nanocrystals (quantum dot solids). We form spherical agglomerates of nano...

Lejun Qi

Papers

Facile synthesis of silver chalcogenide (Ag2E; E=Se, S, Te) semiconductor nanocrystals.

Nanostructured SiC by chemical vapor deposition and nanoparticle impaction

Micropattern deposition of colloidal semiconductor nanocrystals by aerodynamic focusing

Facile Synthesis of Silver Chalcogenide (Ag2E; E: Se, S, Te) Semiconductor Nanocrystals.

Impact dynamics of colloidal quantum dot solids.