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Yang X.,Arizona State University | Froehlich J.D.,Nitto Denko Corporation | Chae H.S.,Nitto Denko Corporation | Harding B.T.,Nitto Denko Corporation | And 4 more authors.
Chemistry of Materials | Year: 2010

The synthesis, photophysical, and electrochemical characterization of macromolecules, consisting of an emissive platinum complex and carbazole moieties covalently attached to a polyhedral oligomeric silsesquioxane (POSS) core, is reported. Organic light-emitting devices based on these POSS materials exhibit a peak external quantum efficiency of ca. 8%, which is significantly higher than that of the analogous devices with a physical blend of the platinum complexes and a polymer matrix, and they represent noticeable improvement in the device efficiency of solution-processable phosphorescent excimer devices. Furthermore, the ratio of monomer and excimer/aggregate electroluminescent emission intensity, as well as the device efficiency, increases as the platinum complex moiety presence on the POSS macromolecules decreases. © 2010 American Chemical Society.

Gullapalli S.,Rice University | Grider J.M.,Rice University | Grider J.M.,University of Texas at Austin | Bagaria H.G.,Rice University | And 7 more authors.
Nanotechnology | Year: 2012

Many colloidal synthesis routes are not scalable to high production rates, especially for nanoparticles of complex shape or composition, due to precursor expense and hazards, low yields, and the large number of processing steps. The present work describes a strategy to synthesize hollow nanoparticles (HNPs) out of metal chalcogenides, based on the slow heating of a low-melting-point metal salt, an elemental chalcogen, and an alkylammonium surfactant in octadecene solvent. The synthesis and characterization of CdSe HNPs with an outer diameter of 15.6 ± 3.5 nm and a shell thickness of 5.4 ± 0.9 nm are specifically detailed here. The HNP synthesis is proposed to proceed with the formation of alkylammonium-stabilized nano-sized droplets of molten cadmium salt, which then come into contact with dissolved selenium species to form a CdSe shell at the droplet surface. In a reaction-diffusion mechanism similar to the nanoscale Kirkendall effect it is speculated that the cadmium migrates outwardly through this shell to react with more selenium, causing the CdSe shell to thicken. The proposed CdSe HNP structure comprises a polycrystalline CdSe shell coated with a thin layer of amorphous selenium. Photovoltaic device characterization indicates that HNPs have improved electron transport characteristics compared to standard CdSe quantum dots, possibly due to this selenium layer. The HNPs are colloidally stable in organic solvents even though carboxylate, phosphine, and amine ligands are absent; stability is attributed to octadecene-selenide species bound to the particle surface. This scalable synthesis method presents opportunities to generate hollow nanoparticles with increased structural and compositional variety. © 2012 IOP Publishing Ltd.

Lee K.-S.,Arizona State University | Lim J.-W.,Kyung Hee University | Kim H.-K.,Kyung Hee University | Alford T.L.,Arizona State University | Jabbour G.E.,Solar and Alternative Energy Engineering Research Center
Applied Physics Letters | Year: 2012

A transparent conductive electrode of mixed titanium dioxide (TiO 2-x)-indium tin oxide (ITO) with an overall reduction in the use of indium metal is demonstrated. When used in organic photovoltaic devices based on bulk heterojunction photoactive layer of poly (3-hexylthiophene) and [6,6]-phenyl C 61 butyric acid methyl ester, a power conversion efficiency of 3.67 was obtained, a value comparable to devices having sputtered ITO electrode. Surface roughness and optical efficiency are improved when using the mixed TiO 2-x-ITO electrode. The consumption of less indium allows for lower fabrication cost of such mixed thin film electrode. © 2012 American Institute of Physics.

Kim I.,Arizona State University | Haverinen H.M.,University of Oulu | Li J.,Arizona State University | Jabbour G.E.,Arizona State University | Jabbour G.E.,Solar and Alternative Energy Engineering Research Center
Applied Physics Letters | Year: 2010

We demonstrate an enhancement in the power conversion efficiency (PCE) of p-i-n type organic solar cells consisting of zinc phthalocyanine (ZnPc) and fullerene (C60) using a p -layer of palladium phthalocyanine (PdPc). Solar cells employing three different device structures such as ZnPc/ZnPc:C60/ C60, PdPc/PdPc:C60/ C60, and PdPc/ZnPc:C60/ C60 with varying thickness of mixed interlayers were fabricated by thermal evaporation. The mixed i -layers were deposited by co-evaporation of MPc (M=Zn,Pd) and C60 by 1:1 ratio. PCE of 3.7% was obtained for optimized cells consisting of PdPc/ZnPc: C60 / C60, while cells with device structure of ZnPc/ZnPc: C60 / C60 showed PCE of 3.2%. © 2010 American Institute of Physics.

Kim I.,Korea Institute of Science and Technology | Jabbour G.E.,Arizona State University | Jabbour G.E.,Solar and Alternative Energy Engineering Research Center
Synthetic Metals | Year: 2012

We investigated the effects of annealing on device performances of bulk heterojunction organic solar cells based on copper phthalocyanine (CuPc) and N,N′-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C6). Blended films of CuPc and PTCDI-C6 with annealing at elevated temperature were characterized by measuring optical absorption, photoluminescence, and X-ray diffraction. Enhanced molecular ordering and increments in domain sizes of donor and acceptor for the blended films were observed, and their influences on device performances were discussed. Annealing led to substantial improvements in photocurrent owing to enhanced molecular ordering and formation of percolation pathways. © 2011 Elsevier B.V. All rights reserved.

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