After more than 20 years of steady progress, lithium-ion batteries still exhibit modest energy capacities that seem to have reached their asymptotic values with the present combination of graphite at the anode and insertion oxide or phosphate materials at the cathode. New applications, particularly for all-electric vehicles are pushing the development of electrode materials with higher Li storage capabilities, for both electrodes.Silicon, which exhibits the highest known Li-alloying capacity is one of the most promising anode materials.However, Li alloying with Si is accompanied by a large volume change which induces cracking and rapid pulverization of Si-based anodes. Significant improvements in the anode's lifetime as well as chargedischarge rates have been obtained over the past few years by employing Si nanostructures, particularly nanowires. In this paper, we present the main synthesis methods for Si nanowires as well as the alloying properties of Li with Si and review how the use of Si-based nanowires has evolved, thanks to sophisticated material/structure combinations, including core-shell nanowires, composites as well as hollowed nanotube-like approaches.

Perovskite quantum dots have recently emerged as a promising light source for optoelectronic applications. However, integrating them into devices while preserving their outstanding optical properties remains challenging. Due to their ionic nature, perovskite quantum dots are extremely sensitive and degrade on applying the simplest processes. To maintain their colloidal stability, they are surrounded by organic ligands; these prevent efficient charge carrier injection in devices and have to be removed. Here we report on a simple method, where a moderate thermal process followed by exposure to UV in air can efficiently remove ligands and increase the photo-luminescence of the room temperature synthesized perovskite quantum dot thin films. Annealing is accompanied by a red shift of the emission wavelength, usually attributed to the coalescence and irreversible degradation of the quantum dots. We show that it is actually related to the relaxation of the quantum dots upon the ligand removal, without the creation of non-radiative recombining defects. The quantum dot surface, as devoid of ligands, is subsequently photo-oxidized and smoothened upon exposure to UV in air, which drastically enhances their photo-luminescence. This adequate combination of treatments improves by more than an order of magnitude the performances of perovskite quantum dot light emitting diodes.

Zinc oxide (ZnO) nanoparticles (NPs) are widely used as electron-transport layers in quantum dots (QDs) light-emitting diodes (QLEDs). In this work, we show that the size of the NPs can be tuned with the sol–gel synthesis temperature while keeping a constant mass yield. As the NP size decreases, the surface defect density reduces and the band gap broadens. In return, it prevents exciton quenching at the ZnO NPs/emitting QDs (core–shell CdSe@ZnS) interface. Moreover, as the conductivity of the ZnO NP films decreases, the electron–hole balance in QLEDs improves. When the synthesis temperature decreases from 60 to 0 °C, the diameter of the NPs shrinks from 5.4 to 2.8 nm. The optical band gap broadens from 3.44 to 3.66 eV and the energy of the minimum of the conduction band increases from −3.81 to −3.64 eV below the Fermi level. Consequently, the radiative decay rate of a CdSe@ZnS QDs layer coated on ZnO NP films increases from 11.62 to 13.75 ns. The smaller NPs exhibit a faceted surface with a lower density of defects. Under UV illumination, the intensity of the band to band emission from the ZnO NPs increases while the emission from defects decreases as the NPs diameter becomes smaller. The conductivity of the ZnO film decreases by more than 1 order of magnitude, and the current efficiency of QLEDs increases from 35.8 to 50.8 cd/A.

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