Duane A. Schneider

Impacts of Humidity and Temperature on the Performance of Transparent Conducting Zinc Oxide

The impact of humidity and temperature on a zinc oxide based transparent conducting oxide (TCO) was assessed under accelerated aging conditions. An in situ electroanalytical method was used to monitor the electrical properties for a conducting zinc oxide under controlled atmospheric (humidity, temperature and irradiation) conditions. A review of thin film photovoltaic (PV) literature has shown one major failure mode of cells/modules is associated with the ingress of water into modules in the field. Water contamination has been shown to degrade the performance of the TCO in addition to corroding interconnects and other conductive metals/materials associated with the module. Water ingress is particularly problematic in flexible thin film PV modules since traditional encapsulates such as poly(ethyl vinyl acetate) (EVA) have high water vapor transmission rates. The accelerated aging studies of the zinc oxide based TCOs will allow acceleration factors and kinetic parameters to be determined for reliability purposes.

Multilayer co-extrusion technique for developing high energy density organic devices.

The purpose of this project is to develop multi-layered co-extrusion (MLCE) capabilities at Sandia National Laboratories to produce multifunctional polymeric structures. Multi-layered structures containing layers of alternating electrical, mechanical, optical, or structural properties can be applied to a variety of potential applications including energy storage, optics, sensors, mechanical, and barrier applications relevant to the internal and external community. To obtain the desired properties, fillers must be added to the polymer materials that are much smaller than the end layer thickness. We developed two filled polymer systems, one for conductive layers and one for dielectric layers and demonstrated the potential for using MLCE to manufacture capacitors. We also developed numerical models to help determine the material and processing parameters that impact processing and layer stability.

Porosity in Polysilsesquioxane Xerogels

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR′) 3 , with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.

Preparation and characterization of phenyl-, benzyl-, and phenethyl-substituted polysilsesquioxanes

Polysilsesquioxanes are a class of siloxane polymers commonly prepared by the hydrolysis and condensation of trialkoxysilanes or trichlorosilanes. From a trifunctional monomer one would expect the organically-modified polymers to be highly crosslinked and insoluble resins. However, while some silsesquioxane monomers with R = H, CH{sub 3}, or vinyl do form crosslinked polymers capable of forming gels, the majority react to form soluble oligosilsesquioxanes, including discrete polyhedral oligomers, and polymers. Because of their solubility, ladder structures have been proposed. However, viscosity studies by Frye indicate that the polyphenylsilsesquioxane is more likely best represented by a polymer rich in both cyclic structures and branches, but without any regular stereochemistry. In this study, the authors have examined the hydrolysis and condensation polymerizations of phenyltrialkoxysilane, benzyltrialkoxysilane, and 2-phenethyltrialkoxysilane monomers under both acidic and basic conditions. The resulting phenyl, benzyl and phenethyl-substituted polysilsesquioxanes were characterized by {sup 1}H, {sup 13}C, {sup 29}Si NMR, gel permeation chromatography, and differential scanning calorimetry. The effects of the organic substituent (phenyl, benzyl, phenethyl), alkoxide group (OMe, OEt), catalyst (HCl, NaOH), monomer concentration, and polymer processing on polymer molecular weight and glass transition temperature were determined.