The 25th International Conference on Amorphous and Nano-crystalline Semiconductors
August 18–23, 2013 Toronto, Ontario Canada
New Nano-materials: Photovoltaics II
Chair: Siva Sivoththaman, University of Waterloo
Molecular Derived Metal Oxide and Chalcogenide Materials with High Potential as Semiconductors, Conductors and Dielectrics for Thin Film Transistor and Solar Cell Applications
Technische Universität Darmstadt, Department of Chemistry, Inorganic Chemistry, Petersenstraße 18, 64287 Darmstadt, Germany
Solution based routes to amorphous metal oxides are attractive since they allow for a low temperature processing of such thin films as functional materials. Especially the possibility that the oxides of element groups 11–14 (Cu, Zn, Cd, Al, Ga, In, Sn, Pb) of the periodic system can form solid solutions allows for a tailoring of the properties of the resulting mixed metal oxides due to their variable composition. With respect to the tailoring of their composition, these mixed metal oxides can be obtained as amorphous or crystalline thin films.
An interesting approach to such solid metal oxide solutions is the usage of well defined molecular complexes which are stable under ambient conditions (air, temperature) which are soluble in a wide variety of solvents, and do not need sophisticated experimental equipment for their handling and application. In order to develop such an access we have introduced a family of metal-oximato complexes which are Schiff-base type coordination compounds.Therein the central metals (Cu, Zn, Cd, Al, Ga, In, Sn, Pb) are coordinated by O and N terminated functional groups. All metal complexes of these ligands display a good solubility in common solvents which make them even attractive for applications in printable electronics. Solutions of these complexes can be combined in various ratios and after thermal processing this opens up a route to access different elemental compositions of crystalline as well as amorphous group 11–14 metal oxides. The decomposition pathway of all metal-oximato complexes into the respective metal oxides MxOy and metal chalcogenides (S, Se) MSx,Sey can be understood using coupled thermogravimetry/spectroscopic studies (TG-MS/IR). All precursor compounds display similar low decomposition temperatures which are between 150°C and 200°C. They convert cleanly into the desired mixed metal oxides and metal chalcogenides, the latter in the presence of an additional molecular sulfur or selenium source.
In our contribution we will report on the synthesis, characterization and thin film transistor properties of a family of crystalline and amorphous binary and ternary metal oxides derived from molecular metal-oximato complexes (metal = Cu, Zn, Cd, Al, Ga, In, Sn, Pb). We will discuss how these complexes can be converted into chemically pure binary and ternary transparent thin films of adjustable elemental composition. These films exhibit excellent material performance as semiconductor, conductor or dielectric material. Examples will be given. Physical characteristics of their functionality in TFT applications will be presented. When using appropriate metal-oximato complexes of copper and indium together with thiourea as chalcogenide source, formation of CuInS2, an established solar cell absorber material can be achieved. When using a polymeric, nano-porous membrane as structure directing template, spatially oriented, three dimensional arrays of CuInS2 nano rods are accessible. Extensive film characterization of all materials will be presented employing a variety of analytical techniques (e.g. SEM, TEM, XPS, GIXRD, AFM, IR reflectometry) Such studies allow insight into the phase composition of the functional thin films which governs their material performance from a chemical viewpoint.
Keywords: metal oxides, molecular precursor, semiconductor, dielectric, thin films, amorphous, nanocrystalline, TFT
Effect of Graphene on Photocatalysis of Titanium Dioxide Thin Films
School of Chemical and Materials Engineering, National University of Sciences and Technology (NUST), H-12, Islamabad
Graphene, having remarkable properties like high surface area, superior electronic and optical properties, has emerged as one of best constituent material for photovoltaic devices. The main goal of this research is to investigate the effect of graphene amount on photocatalysis of titania thin films. Graphene was synthesized by modified Hummer's method and subsequently reduced before using for film fabrication. Titania sol was prepared which was mixed with varying amount of reduced graphene. Multilayer thin films were deposited by dip-coating on glass and ITO substrates. Resulting composite films were characterized by SEM for morphological evolution of mesoporous titania thin films and uniform dispersion of graphene, XRD for phase analysis revealing high amount of anatase and UV-Vis spectrophotometer for studying optical properties. An increase of photocatalytic activity was found with increasing graphene amount and reduction of band gap upto 2.9 eV was obtained.
Keywords: titania, thin films, graphene, photocatalysis, photovoltaic cells