The direct UV irradiation of nanoparticulate TiO 2 films deposited by the "doctor-blade" technique led to 1.1 µm thick nanoporous and nanocrystalline anatase layers on various kinds of substrates as evidenced by various characterization techniques (MET, SEM, XRD, TGA-MS, and N 2 sorption measurements). These films demonstrated high electrochromic responses and coloration efficiencies in an ionic liquid containing a lithium salt, which is a stable and environmental friendly electrolyte. The coloration efficiency reached 38 cm 2 C -1 for films on ITO/plastic, for a 0.65 absorption change at 710 nm, whereas the corresponding film on FTO/glass showed a 40 cm 2 C -1 coloration efficiency for a 1.1 absorbance change at 710 nm. The high surface area, nanoporous texture, and nanoparticulate structure of these layers provide a large number of intercalation sites, and minimal diffusion path lengths are ensured by the high surfaceto-volume ratio.
SnO2 translucent monolith ionogels were obtained by a sol-gel processing using bis(2-methylbutan-2-oxy)di(pentan-2,4-dionato)tin as a precursor in the presence of various ionic liquids: [BMI][Br], [BMI][TFSI], [BMI][BF4]. The confinement of ionic liquids within the gels was evidenced by Differential Scanning Calorimetry, FTIR and FT-Raman spectroscopy. The ionic liquids could be efficiently washed off, which resulted in supermicroporous solids. Calcination in air at 550 degrees C of the dried monoliths resulted in nanoporous nanocrystalline cassiterite tin dioxide particles with crystallite sizes of about 8-12 nm and mean pore sizes around 5 nm.
Connection of SnO₂ particles by simple UV irradiation in air yielded cassiterite SnO₂ porous films at low temperature. XPS, FTIR, and TGA-MS data revealed that the UV treatment has actually removed most of the organics present in the precursor SnO₂ colloid and gave more hydroxylated materials than calcination at high temperature. As electrodes for dye-sensitized solar cells (DSCs), the N3-modified 1-5 μm thick SnO₂ films showed excellent photovoltaic responses with overall power conversion efficiency reaching 2.27% under AM1.5G illumination (100 mW cm⁻²). These performances outperformed those of similar layers calcined at 450 °C mostly due to higher V(oc) and FF. These findings were rationalized in terms of slower recombination rates for the UV-processed films on the basis of dark current analysis, photovoltage decay, and electrical impedance spectroscopy studies.
Increasing solar cell efficiency by using spectral conversion is addressed in this article. To that purpose rare-earth doped YAG nanoparticles exhibiting down-conversion and quantum cutting properties have been prepared. These nanoparticles have been synthesized with different concentrations of dopants in order to optimize the luminescence and the quantum cutting efficiency. Results on the incorporation of selected material into the encapsulating layer of c-Si based PV-modules are also presented. The effect of down-conversion has been demonstrated through the increase of photocurrent of encapsulated silicon solar cells.
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