No abstract

are an emerging class of materials used in energy conversion systems, owing to their high absorption coefficients, nontoxicity, and appropriate band gaps. Their properties can be tuned by varying their size and composition, and they are characterized by peculiar photophysical properties due to a high density of intra band gap electronic states, which arise from defects in the crystal structure and from trap states at the surface. In this Perspective we first discuss optical and electrochemical studies, which give insight into the electronic structure of chalcopyrite nanocrystals. In the second part, their exploitation for energy conversion is highlighted, in particular their use in photovoltaics (with power conversion efficiencies already exceeding 10%) as well as in luminescent solar concentrators, photocatalytic systems, and thermoelectrics. Finally, we discuss current challenges in the chemistry and applications of the title compounds.

Cadmium-free CuInS2/ZnS quantum dots as very efficient and robust photosensitizers for photocatalytic hydrogen production with a molecular cobalt catalyst.

Ternary metal chalcogenide nanocrystals (NCs) offer exciting opportunities as novel materials to be explored on the nanoscale showing optoelectronic properties tunable with size and composition. CuInS (CIS) NCs are the most widely studied representatives of this family as they can be easily prepared with good size control and in high yield by reacting the metal precursors (copper iodide and indium acetate) in dodecanethiol (DDT). Despite the widespread use of this synthesis method, both the reaction mechanism and the surface state of the obtained NCs remain elusive. Here, we perform in situ X-ray diffraction using synchrotron radiation to monitor the pre- and postnucleation stages of the formation of CIS NCs. SAXS measurements show that the reaction intermediate formed at 100 °C presents a periodic lamellar structure with a characteristic spacing of 34.9 Å. WAXS measurements performed after nucleation of the CIS NCs at 230 °C demonstrate that their growth kinetics depend on the degree of precursor conversion achieved in the initial stage at 100 °C. NC formation requires the cleavage of S-C bonds. We reveal by means of combined 1D and 2D proton and carbon NMR analyses that the generated dodecyl radicals lead to the formation of a new thioether species R-S-R. The latter is part of a ligand double layer, which consists of dynamically bound dodecanethiolate ligands as well as of head-to-tail bound R-S-R molecules. This ligand double layer and a high ligand density (3.6 DDT molecules per nm) are at the origin of the apparent difficulty to functionalize the surface of CIS NCs obtained with the DDT method.

Silicon (Si) is the most promising anode candidate for the next generation of lithium-ion batteries but difficult to cycle due to its poor electronic conductivity and large volume change during cycling. Nanostructured Si-based materials allow high loading and cycling stability but remain a challenge for process and engineering. We prepare a Si nanowires-grown-on-graphite one-pot composite (Gt-SiNW) via a simple and scalable route. The uniform distribution of SiNW and the graphite flakes alignment prevent electrode pulverization and accommodate volume expansion during cycling, resulting in very low electrode swelling. Our designed nano-architecture delivers outstanding electrochemical performance with a capacity retention of 87% after 250 cycles at 2C rate with an industrial electrode density of 1.6 g cm -3 . Full cells with NMC-622 cathode display a capacity retention of 70% over 300 cycles. This work provides insights into the fruitful engineering of active composites at the nanoand microscales to design efficient Si-rich anodes.

Stable fluorescent chromophores find use in a growing number of practical applications, including their utility as laser dyes, 1 emitters in light-emitting diodes, 2 photoconductors, 3 optical data storage, 4 and optical switches. 5 Stable fluorophores with high quantum yields are widely used in fluorescent sensors 6 and labels. 7 These became very popular lately, owing to their potential for high sensitivity at low concentration coupled with decreased cost of the required equipment. 8 Recently, we have described a new class of fluorescent anion sensors bearing extended conjugated chromophores 9 with incorporated 2,3-di(1H-2-pyrrolyl)quinoxaline, (DPQ), as the anion recognition element. 10 Literature shows that DPQ binds anions via hydrogen bonding between pyrrole NH and anions, the hydrogen bonding nature of the DPQ-anion complex was demonstrated by 1 H NMR. 10a In this paper, we provide a full account of our efforts including synthesis and photophysical properties of DPQ-based fluorescent anion sensors with extended conjugated chromophores S1-S6 (Figure 1), including their benzothiadiazole precursors F1-F6, which appears to be an interesting set of highly stable fluorescent chromophores.Sensors S1-S6 with the extended aryl substituents of varying electronic nature were designed to provide a tool for systematic modulation of electronic density in the quinoxaline chromophore. This, in turn, was expected to lead to tuning the output emission wavelength as well as the anion binding affinity in the sensors S1-S6. Our previous studies suggest that even small changes in electronic density in the quinoxaline moiety affect the pyrrole hydrogen-bonding donors and the stability of the anion-sensor complex. 9a

Electrodeposited copper thiocyanate (CuSCN) thin films and nanowires have been investigated by X-ray photoelectron spectroscopy (XPS), Raman and optical spectroscopy. In addition, atomic force microscopy (AFM), together with scanning and transmission electron microscopy (SEM, TEM), have been employed for structural characterisation. The multiple technique approach allows the correlation between structural, chemical and electrical properties that are unique to the structure of this material. It has been found that CuSCN thin films and nanowires exhibit high crystalline quality with a close to stoichiometric composition. The XPS and Raman spectra suggest that the thiocyanate ion is bound to copper mainly through its Send , with approximately 12-14 % bound via the N-end. The applied absorption spectroscopy (Tauc and Urbach plots) points towards the possible coexistence of two large band gaps for the electrodeposited CuSCN. While its interpretation may be problematic from a purely physical perspective, we believe that this is a direct consequence of the occurrence of two CuSCN domains identified by XPS and Raman. A prominent absorption tail is observed that is assigned as either being due to the high concentration of the traps, or a result of coexisting CuSCN domains. This absorption tail should not be an obstacle for the use of the copper thiocyanate in electronic devices, as the traps density could be reduced by annealing. In addition, non-annealed electrodeposited CuSCN thin films and nanowires of this type have recently been integrated into polymer solar cells and high efficiency has been obtained.

Tin sulfide nanoparticles have a great potential for use in a broad range of applications related to solar energy conversion (photovoltaics, photocatalysis), electrochemical energy storage, and thermoelectrics. The development of chemical synthesis methods allowing for the precise control of size, shape, composition, and crystalline phase is essential. We present a novel approach giving access to monodisperse square SnS nanoplatelets, whose dimensions can be adjusted in the range of 4-15 nm (thickness) and 15-100 nm (edge length). Their growth occurs via controlled assembly of initially formed polyhedral seed nanoparticles, which themselves originate from an intermediate tetrachlorotin-oleate complex. The SnS nanoplatelets crystallize in the α-SnS orthorhombic herzenbergite structure (space group Pnma) with no evidence of secondary phases. Electron tomography, high angle annular dark field scanning transmission electron microscopy and electron diffraction combined with image simulations evidence the presence of ordered Sn vacancy rich (100) planes within the SnS nanoplatelets, in accordance with their slightly S-rich composition observed. When using elemental sulfur instead of thioacetamide as the sulfur source, the same reaction yields small (2-3 nm) spherical SnS2 nanoparticles, which crystallize in the berndtite 4H crystallographic phase (space group P3m1). They exhibit quantum confinement (E(g) = 2.8 eV vs 2.2 eV in the bulk) and room temperature photoluminescence. By means of electrochemical measurements we determined their electron affinity EA = -4.8 eV, indicating the possibility to use them as a substitute for CdS (EA = -4.6 eV) in the buffer layer of thin film solar cells.