We obtained Gallium-doped and Aluminum-doped Zinc Oxide nanocrystals by non aqueous colloidal heat-up synthesis. These nanocrystals are transparent in the visible range but exhibit localized surface plasmon resonances (LSPRs) in the near IR range, tunable and shiftable with dopant concentration (up to 20% mol nominal). GZO and AZO inks can be deposited by spin coating, dip coating or spray coating on glass or silicon, leading to uniform and high optical quality thin films. To enhance absorbtion in the infrared region, samples can be annealed in inert or reductant atmosphere (N2/Argon or H2 in Argon) resulting in plasmon intensity enhancement due to oxygen vacancies and conduction band electrons density increment. Then IR plasmon has been exploited for gas sensing application, according to the plasmon shifting for carrier density variations, due to electrons injection or removal by the target gas/sample chemical interactions. To obtain a functional sensor at low temperature, another treatment was investigated, involving surfanctant removal by dipping deposited films in a solution of organic acid, tipically oxalic acid in acetonitrile; such process could pave the way to obtain similar sensors deposited on plastics. Finally, GZO and AZO thin films proved sensibility to H2 and NOx, and in particular circumstances also to CO, from room temperature to 200°C. Sensibility behavior for different dopant concentration and temperture was investigated both in IR plasmon wavelengths (~2400 nm) and zinc oxide band gap (~370 nm). An enhancement in sensitivity to H2 is obtained by adding Pt nanoparticles, exploiting catalytic properties of Platinum for hydrogen splitting.
Next-generation solar cells will be fabricated from low-cost and earth abundant elements, using processes that are
amenable to printing on a variety of light-weight substrates. The utilization of compositionally and structurally controlled
colloidal nanocrystals as building blocks for such devices fulfills these criteria. Our recent efforts in developing kesterite
Cu2ZnSnS4 (CZTS) nanocrystals, one of the most promising materials to emerge in this area, enable the deposition of CZTS thin-films directly from a variety of solution-processed methods. Nanocrystalline thin films possess poor
electronic properties, which precludes their use in solar cell devices. In order to overcome this, thermal treatment steps
under an atmosphere of vaporous selenium are applied to induce large scale crystallite growth and the production of
selenized CZTSSe films. This process results in a highly photoactive p-type layer. The n-type cadmium sulfide layer is
also deposited from solution using chemical bath deposition. We will discuss each of these accomplishments in detail,
highlighting the significant challenges that need to be overcome in order to fabricate working CZTSSe thin film solar
cells.
Au and Pt nanoparticles are prepared with colloidal techniques in order to achieve high morphological quality, capped
with a polymer and then embedded inside a TiO2 sol-gel matrix, resulting in a homogeneous dispersion of both metal
colloids, confirmed by TEM analyses. Refractive index values measured with ellipsometry increase with the annealing
temperature, with quite a linear trend, and at the same time the Au surface plasmon resonance peak undergoes a red shift:
the refractive index evaluated from the Au plasmon band is slightly lower than the measured value, indicating that the
refractive index just around metal particles is different from the average of the matrix, likely because of the polymeric
capping agent. Optical gas sensing tests towards CO and H2 are presented as one of the possible applications of these
nanocomposites.
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