36 research outputs found
VezetĂ©si kihĂvĂĄsok a magyarorszĂĄgi magyarânĂ©met vĂĄllalatoknĂĄl Az IMAGINE-projekt (Investigation of Management performance in INternational Enterprises) legfontosabb eredmĂ©nyei
A Pannon Egyetem Szervezési és Vezetési Tanszéke a Darmstadti MƱszaki Egyetem Vållalatvezetési Tanszékével
közösen több mint egy Ă©vtizede folytat a stratĂ©giai menedzsment terĂŒletĂ©n, ezen belĂŒl a vĂĄllalati
Ă©s nemzeti kultĂșrĂĄkkal Ă©s a vĂĄllalati sikerrel kapcsolatos kutatĂĄsokat. A napjainkra befejezett IMAGINEprojekt
(Investigation of Management performance in International Enterprises) a magyarorszågi tevékenységet
folytatĂł magyarânĂ©met transznacionĂĄlis vĂĄllalatok vezetĆire fĂłkuszĂĄl. A projekt a vezetĂ©si stĂlust
Ă©s a vezetĂ©s sikerĂ©t meghatĂĄrozĂł tĂ©nyezĆk elemzĂ©sĂ©vel foglalkozik. Ezek az összefĂŒggĂ©sek a gyakorlat szĂĄmĂĄra
is hasznosĂthatĂł eredmĂ©nyeket jelenthetnek. A szerzĆk összesen 86, MagyarorszĂĄgon mƱködĆ magyar-
nĂ©met vĂĄllalat felsĆ vezetĆje ĂĄltal kitöltött kĂ©rdĆĂvet elemeztek
Carbon nanotubes as electronic interconnects in solid acid fuel cell electrodes
Carbon nanotubes have been explored as interconnects in solid acid fuel cells to improve the link between nanoscale Pt catalyst particles and macroscale current collectors. The nanotubes were grown by chemical vapor deposition on carbon paper substrates, using nickel nanoparticles as the catalyst, and were characterized using scanning electron microscopy and Raman spectroscopy. The composite electrode material, consisting of CsH_2PO_4, platinum nanoparticles, and platinum on carbon-black nanoparticles, was deposited onto the nanotube-overgrown carbon paper by electrospraying, forming a highly porous, fractal structure. AC impedance spectroscopy in a symmetric cell configuration revealed a significant reduction of the electrode impedance as compared to similarly prepared electrodes without carbon nanotubes
Polymer-Free Carbon Nanotube Based Solar Cells
Since their discovery in 1991 and 1994 by Iijima, multi walled (MWCNTs) and single walled carbon
nanotubes (SWCNTs) have gained a lot of interest in the research community due to their unique
mechanical (higher tensile strength than stainless steel), optical (multiple excitonic transitions) and
electrical (intrinsic mobility of 105 cm2 Vâ1 sâ1) properties. Being produced as black powder that
contains roughly 1/3 metallic and 2/3 semiconducting nanotubes along with residual catalytic
particles, carbon residues or defected nanotubes, it is important to further purify the raw nanotube
powder to obtain pristine nanotubes only that can be used to exploit these remarkable properties.
In order to incorporate SWCNTs as semiconducting channel material or as electrodes in
transistors, it is of great importance to separate SWCNTs based on their electronic properties.
Whereas, for optoelectronic applications, like photon emitters or solar cells it is necessary to sort
semiconducting SWCNTs into chirality pure fractions with unique absorption features, i.e. the
sorted nanotubes absorb at precise wavelengths (in the infrared, visible and UV). It is this ability to
select SWCNTs with desired optical gaps that make SWCNTs an interesting material that also
offers potential avenues to tailor or extend the light absorption within established solar cells.
Through careful combination of the appropriate chiralities, a close match to the solar spectrum
either in the visible or the infrared is possible.
To realize this vision of tailored light absorption, large amounts of purified, electronic type sorted
and chirality enriched SWCNTs are needed. In this thesis, an automated aqueous based gel
permeation chromatography (GPC) is used to sort milligrams of polymer-free single chirality
enriched nanotube material, where the exciton diffusion length is not limited by a wrapping
polymer. Depending on the temperature, surfactant concentration and eluent differently coloured
solutions are obtained that can be electronic type pure, chirality pure or a mixture of chiralities
and/or electronic types. In order to prevent internal shorts, SWCNTs employed in solar cells need
to obtain as little metallic nanotubes as possible. It is therefore crucial to easily and reliably
characterize the sorted nanotube solutions with respect to the contained chiralities and
semiconducting or metallic purity.
One way of realizing such a characterization is optical absorption spectroscopy. A MATLABÂź
based program was developed throughout this thesis that is capable of addressing several issues
involved in optical absorption spectroscopy of solutions: different approaches for background
subtraction, the choice of different line profiles, the individual fit of the first or second transition (in
the infrared and visible, respectively) or both at the same time and the inclusion of metallic
nanotubes that allows for the evaluation of the metallic/semiconducting purity. Based on the
spectral weight of each nanotube species identified in solution, absorbance spectra of carbon
iv
nanotube films can be fitted, where overlapping peaks are decongested into individual nanotube
contributions.
Following the sorting and characterization of single chirality SWCNTs, large-area films of (6,5)
SWCNTs with uniform morphology are prepared using evaporation-driven self-assembly. The
obtained SWCNT films are incorporated in an organic solar via a transfer process developed
throughout this thesis that prevents the decomposition of hygroscopic layers in the solar cell. In
conjunction with C60 a bi-layer organic solar cell with an all carbon donor and acceptor pair is
formed. Transfer matrix calculations (TMCs) are employed to optimize the layer thicknesses of the
solar cell in order to match the light intensity at the nanotubes first optical transition (in the
infrared), their second transition (in the visible) or a combination thereof. The validity of this
approach is verified by a detailed parameter study resulting in cutting edge internal quantum
efficiency (IQE) of 86% through the nanotubes first transition.
Having established a reliable solar cell architecture resulting in large IQE values for small diameter
SWCNTs (large bandgap), the feasibility of preparing transparent organic solar cells from large
diameter SWCNTs (small bandgap) in combination with C60 is tested by preparing organic solar
cells from single chirality large diameter SWCNTs as well as mixtures of nanotubes with varying
diameters. By carefully decongesting film absorption spectra and associated external quantum
efficiency measurements, the nanotube diameter resulting in 0 % IQE is determined. Underlying
mechanisms of this limit are discussed and possible strategies to circumvent this cut-off are
presented in order to extend the absorption range beyond the (8,6) SWCNT with a diameter of
0.95 nm