Nanostructured semiconductor materials for dye-sensitized solar cells

Since O'Regan and Grätzel's first report in 1991, dye-sensitized solar cells (DSSCs) appeared immediately as a promising low-cost photovoltaic technology. In fact, though being far less efficient than conventional silicon-based photovoltaics (being the maximum, lab scale prototype reported efficiency around 13%), the simple design of the device and the absence of the strict and expensive manufacturing processes needed for conventional photovoltaics make them attractive in small-power applications especially in low-light conditions, where they outperform their silicon counterparts. Nanomaterials are at the very heart of DSSC, as the success of its design is due to the use of nanostructures at both the anode and the cathode. In this review, we present the state of the art for both n-type and p-type semiconductors used in the photoelectrodes of DSSCs, showing the evolution of the materials during the 25 years of history of this kind of devices. In the case of p-type semiconductors, also some other energy conversion applications are touched upon. © 2017 Carmen Cavallo et al

Solid solutions of rare earth cations in mesoporous anatase beads and their performances in dye-sensitized solar cells

Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1-0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m2/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J-V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr3+, Nd3+) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm3+ onwards enhance the performance of the devices. A maximum conversion efficiency of 8.7% for Er3+ at a concentration of 0.2% has been achieved. This is a remarkable efficiency value for a DSSC employing N719 dye without co-adsorbents and a nonvolatile electrolyte. For each RE cation the maximum performances are obtained for a concentration of 0.2% metal atoms. © 2015, Nature Publishing Group. All rights reserved

A new synthesis route to light lanthanide borides: borothermic reduction of oxides enhanced by electron beam bombardment.

Praseodymium hexaboride, uncontaminated by other boride phases, has been quantitatively synthesized in a short time, at the very high temperatures obtainable by electron beam bombardment. The synthesis is carried out in vacuum (similar to5 X 10(-5) mbar) and, after a short annealing, the product is obtained as pure phase which does not require further purification. (C) 2002 Elsevier Science B.V. All rights reserved

High temperatures gas-solid reactivity of aluminum-carbon nanotubes composites

The gas-solid reactivity of metal-carbon matrix composites such as aluminum-carbon nanotubes (Al-CNT) sintered samples was studied at temperatures below and above the melting point of Al in O2, synthetic air,CO2, H2-Ar (5% v/v) and Ar. Small cylindrical samples of different composition with “single-walled” CNTs (SWCNTs) or “multi-walled” (MWCNTs) were sintered in Ar at 625 °C and the resulting materials showeddensities ranging from 92.2 to 99.0% of the theoretical density of bulk Al. Thermogravimetric analysis(TG) with simultaneous differential thermal analysis (DTA) up to 1200 °C shows that the Al-CNT composites do not behave as a two independent phases system. This is mainly demonstrated by the following phenomena: i. The lowering of the melting point of Al, the magnitude of which cannot be explainedby the expected very low solubility of C in Al at this temperature; ii. The amount of Al2O3 grown in oxidizing atmospheres and at the highest temperatures depends from the CNT content in the compos-ite; iii. The formation of Al4C3 occurs only in presence of molten Al as shown by environmental X-ray diffraction “XRD”. Field emission scanning electron microscope “FESEM” and high-resolution analytical transmission electron microscopy “HRTEM” investigations confirm that at the sintering temperature no detectable chemical interaction exists between Al and CNT

Growth of Oxide Films on Refractory Carbide Single Crystals

Ed. P. Vincenzin