Design of CdS Quantum Dots / Multi-Walled Carbon Nanotubes Hybrid Structures for Photovoltaic Applications
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Design of CdS Quantum Dots / Multi-Walled Carbon Nanotubes Hybrid Structures for Photovoltaic Applications Fayna Mammeri1, Andrea Ballarin1,2, Marion Giraud1, Lydie Vivet1, Frederic Herbst1, Carole Connan1, Mohamed M. Chehimi1, Giovanna Brusatin2 and Souad Ammar1 1 ITODYS, Univ Paris-Diderot, Sorbonne Paris Cité, UMR 7086 CNRS, Bâtiment Lavoisier, 15 rue Jean-Antoine de Baïf, F-75013 Paris, France. 2 Dipartimento di Ingegneria Meccanica, Università degli Studi di Padova, Via Marzolo 9, I35131 Padova, Italy. ABSTRACT This paper presents the preparation of multi-walled carbone nanotubes (CNTs) and CdS nanoparticles based hybrid materials. We aim at comparing two kinds of CNTs’ functionalization by thiol groups in order to demonstrate that the surface chemistry done on the CNTs can direct the morphology of the nanohybrids. Indeed, strong oxidation of CNTs leads to shorter nanotubes opened at their ends, allowing the grafting of mercaptotriethoxysilane whereas the generation of diazonium salts in presence of pristine nanotubes should lead to the functionalization of the whole lateral surface of the nanotubes. CdS nanoparticles can then be anchored to thiol groups, leading to interesting hybrid precursors for photovoltaic applications. INTRODUCTION Dye-sensitized solar cells (DSSCs) are significantly interesting in the development of environmentally friendly energy resources due to their simple fabrication process, low production cost and high efficiency.1 Titanium dioxide nanoparticles have been widely used as a working electrode because they provide a higher efficiency than any other metal oxide semiconductor.2 Nevertheless, the key problem is still to achieve higher photoconversion efficiency in nanostructured electrodes.3 Recent progress in carbon nanotubes (CNTs) based nanocomposites and nanostructures development and fabrication make them attractive to direct the flow of photogenerated electrons to the collecting electrode surface in a DSSC. Semiconducting (essentially chalcogenide) nanoparticles are also studied because these quantum dots are offering two main possibilities for improving the efficiency of solar cells: the modulation of the band gap of solar cells for harvesting more of the light in the solar spectrum, and the generation of more charges from a single photon. Research is currently focused on CdS quantum dots 4 even if other semi-conductor nanoparticles like CdSe and CdTe can induce charge-transfer processes under visible light irradiation when anchored to CNTs.5 In this context, semiconductor nanoparticles and carbon nanotubes hybrid architectures appear promising to develop new generation solar cells. Hence, we developed CdS quantum dots / carbon nanotubes hybrid structures in order to build nanoscale assemblies for photovoltaic cells. 6 nm mean diameter CdS nanoparticles were synthesized by the polyol method,6 a versatile chemical route for the preparation of highly crystalline, monodisperse, metal, oxide or sulfide nanoparticles starting from metallic salts precursors.7,8 Then, carbon nanotubes (
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