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Oxido de niobio enxertado sobre a superficie da silica gel : preparação e utilização na construção de eletrodos modificadosPessoa, Christiana Andrade 31 July 2018 (has links)
Orientador : Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-07-31T18:39:49Z (GMT). No. of bitstreams: 1
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Previous issue date: 2001 / Doutorado
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Propriedades magnéticas e estruturais do composto Y3(Fe1-xZnx)5O12GARCIA, Ramón Raudel Peña 04 January 2017 (has links)
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Previous issue date: 2017-01-04 / CNPQ / No presente trabalho foram investigadas as propriedades magnéticas e estruturais do
composto Y3(Fe1-xZnx)5O12, (x = 0; 0,01; 0,03; 0,05), obtido pelo método sol gel.
Também, foram estudados filmes finos de Y3Fe5O12, preparados pelo método de
deposição de soluções químicas (sol gel). Para ambos os estudos, utilizaram-se técnicas
de caracterização estrutural, morfológica e magnética. Para a síntese das nanopartículas
de Y3(Fe1-xZnx)5O12 foram utilizados materiais à base de nitratos e água destilada como
solvente. As temperaturas características da decomposição do material foram analisadas
utilizando a técnica termogravimétrica e calorimetria diferencial de varredura. Este
estudo mostrou que existem várias etapas na formação do material, relacionadas com as
perdas de água e de materiais orgânicos e com a formação da fase cristalina. Três
famílias de amostras foram sinterizadas nas temperaturas seguintes: i) 900°C, ii)
1000°C iii) 1100°C. A caracterização estrutural do primeiro grupo (900°C) apresentou
uma única fase cristalográfica, correspondente à granada de ítrio e ferro. O aumento
observado no parâmetro de rede foi relacionado com o maior raio iônico do Zn2+ em
relação ao do Fe3+. A morfologia dos grãos foi determinada utilizando a técnica de
microscopia eletrônica de varredura, mostrando formatos alongados e aumento do
tamanho dos aglomerados com o incremento da concentração de Zn2+. O pico referente
ao íon de Zn2+ foi observado mediante a técnica de Espectroscopia de energia
dispersiva, corroborando sua presença dentro da estrutura cúbica da granada. A
espectroscopia Raman revelou um aumento da intensidade na banda principal (271,8
cm-1) com o incremento da dopagem. A análise magnética mostrou um incremento na
magnetização de saturação para a amostra dopada em 1%, enquanto uma diminuição foi
observada para as maiores concentrações de Zn2+, associada ao enfraquecimento do
acoplamento magnético no sítio octaédrico. A análise estrutural da segunda família de
amostras (1000°C) indicou a presença de uma nova fase cristalográfica, pertencente à
fase ortorrômbica do YIG, representando 2 % do total da amostra; ao mesmo tempo, no
terceiro grupo de amostras (1100°C), se observaram reflexões típicas do composto
franklinita. Estes resultados, junto ao observado nas curvas de TG-DSC, sugeriram a
presença de um composto metaestável. O momento magnético em função do campo
aplicado, na família de amostra sinterizada a 1000°C, apresentou uma diminuição na
magnetização de saturação com o incremento da concentração de Zn2+. As curvas da
magnetização em função da temperatura foram ajustadas a partir da lei de Bloch,
obtendo valores similares aos reportados na literatura para o YIG dopado com outros
íons. Para a preparação dos filmes de Y3Fe5O12, foi desenvolvida uma metodologia
química geral, a qual tem por base o álcool isopropílico, usado como solvente na
primeira família de filmes e 2-methoxyethanol como solvente na síntese modificada. A
caracterização estrutural dos filmes obtidos com álcool isopropílico mostrou a fase
cristalográfica ortorrômbica como majoritária e picos que cristalizam na fase cúbica.
Além disso, todos os filmes apresentaram deformações morfológicas provocadas pela
interação filme-substrato de silício. A largura de linha por FMR obtida encontra-se entre
75 e 78 Oe. No filme obtido a partir da síntese modificada observou-se a fase cúbica do
YIG como predominante, com pequenas reflexões da fase ortorrômbica. A imagem de
microscopia eletrônica de varredura mostrou a formação de um filme uniforme, com
uma pequena quantidade de poros distribuída uniformemente na superfície. A medida
de ressonância ferromagnética com o ajuste mostrou uma largura de linha de 53 Oe.
Correspondendo ao valor mais baixo reportado na literatura para filmes finos de YIG
sobre substrato de silício e usando métodos químicos. / The magnetic and structural properties of Y3(Fe1-xZnx)5O12, (x = 0; 0,01; 0,03; 0,05)
obtained by the sol gel method were investigated. As well, thin films of Y3Fe5O12,
prepared using spin-coating of chemical solutions (sol-gel) were characterized. The
synthesis of Y3(Fe1-xZnx)5O12 nanoparticles was using precursors based on nitrates and
distilled water as the solvent. The decomposition temperatures of dried gel were
examined using the Thermogravimetry and Differential Scanning Calorimetry
techniques. There are several steps in the decomposition of the dried gel; related to the
loss of water and organic materials, as well as the formation of the crystalline phase.
Three families of samples were prepared at different temperatures of the thermal
treatment: i) 900°C, ii) 1000°C and iii) 1100°C. The structural characterization of the
first group (900°C) presented a single crystallographic phase, corresponding to the
yttrium iron garnet. The increasing in lattice parameter was associated to the largest
ionic radius of Zn2+ ions compared to the Fe3+ ions. The morphology of the grains was
determined using scanning electron microscopy, showing elongated shapes and a
growing of agglomerates as Zn2+ concentration increases. The characteristic peak of
Zn2+ was observed by Dispersive Energy Spectroscopy, increasing the intensity with the
dopant concentration, corroborating the presence of the element within the cubic
structure of the garnet. Raman spectroscopy revealed an increasing in the main band
(271.8 cm-1) and the octahedral sites are more likely for the substitution of Fe3+ by Zn2+.
The measurements showed the maximum value for magnetic saturation in the 1% doped
sample, while a decreasing was observed for highest concentrations of Zn, associated to
the weakening of the magnetic coupling across the octahedral site. The structural
analysis of the second group of samples (1000°C heat treatment), showed the yttrium
iron garnet and the orthorhombic phase (until 2%). The third group of samples (1100°C
heat treatment) showed yttrium iron garnet and the orthorhombic phase (until 4%) and
typical reflections of Franklinite (until 4%). The magnetic moment versus the applied
field, in the family of samples sintered at 1000°C, showed a decreasing in the saturation
magnetization as Zn2+ concentration increases. The results of fittings according to
Bloch's law showed magnetic parameters similar in values, compared to those reported
in the literature for YIG doped with other ions. The second part of our study aim the
preparation of thin films of Y3Fe5O12 using sol gel based in isopropyl alcohol (in the
first tentative) and 2-methoxyethanol in the modified synthesis. The structural
characterization of samples obtained using isopropyl alcohol, showed the orthorhombic
crystallographic phase as majority and peaks of the cubic phase. All samples showed a
cracked morphology due to the film-substrate interaction and the FMR linewidth ranges
from 75 Oe until 78 Oe. In the film obtained from the modified synthesis (using 2methoxyethanol),
we observed the majoritary cubic phase of YIG and small reflections
of the orthorhombic phase. The scanning electron microscopy image shows a uniform
film with pores evenly distributed on the surface. The ferromagnetic resonance
measurement and the fitting by the derivative of the Lorentzian function, showed a
linewidth of 53 Oe. It is the lowest value reported in the literature for thin films of YIG
on silicon substrate and using chemical methods.
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Sintese, caracterização e algumas propriedades do oxido de tetanio (IV) enxertado sobre superficie de silica gelKubota, Lauro Tatsuo, 1964- 18 July 2018 (has links)
Orientador : Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-07-18T07:36:00Z (GMT). No. of bitstreams: 1
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Previous issue date: 1993 / Doutorado
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Gel-based solid dosage form for pesticide deliveryMassinga, Pedro Horacio 26 March 2008 (has links)
The aim of this research was to develop a solid dosage form containing 1.5 g of the pesticide cypermethrin. The dosage should be stable in a tropical climate. In addition, it is to disintegrate and disperse in 10 L of tap water within 3 minutes. Such dissolution should yield a 150 ppm dispersion of cypermethrin, stable for at least one week. This provides for a dip dispersion to treat ticks and fly infestation on livestock. A new solid dosage was formulated as the scope of this research. It is a gel-based solid dosage form. Polymer electrolyte ASP4 - a copolymer of methacrylic acid, ethyl acrylate and diethyl maleate, was used to produce the gel. Preliminary tests revealed that ASP4- based gel, on its own, failed to meet the required dissolution time of 3 minutes. Strong entanglements of ASP4 chains impeded rapid dissolution. These strong entanglements occurred owing to the use of a high concentration of ASP4. Reducing the concentration of ASP4 yielded a solution of high viscosity instead of a gel. It was therefore decided to Gel-based solid dosage form for pesticide delivery use a superabsorbent (Product Z1069) in conjunction with ASP4 to produce the gel. Product Z1069 is a cross-linked sodium polyacrylate. Before producing the gel, a 1:1.5 by mass oil/water (O/W) emulsion was prepared using the phase-inversion route. The water (W) phase comprised 85.9% distilled water, 3.9% ASP4 at 20% dispersion, 8.6% sodium carbonate (0.5 M) and 1.6% Emulsogen EL. All concentrations are indicated in mass %. The oil (O) phase consisted of 76.9% cypermethrin, 19.3% Solvesso S200 and 3.8% Phenyl Sulphonate CA, also by mass. This emulsion was gelled by adding the superabsorbent Product Z1069 (ca. 37.5% by mass relative to the W phase of the emulsion). The superabsorbent strongly absorbed water, depleting it from the emulsion. This resulted in an increase of the effective concentration of ASP4 in the water phase of the emulsion. This increase of the polymer electrolyte concentration brought about a gel-like state corresponding to the desired solid dosage form. Rheometry confirmed that the dosage form maintained a solid gel-like consistency at 50°C. The dosage contained 24.6% m/m cypermethrin. Thus, the required dosage of 1.5 g was achieved in pellets weighing ca. 6.1 g. Such pellets rapidly disintegrated with mild stirring in 10 L of tap water. Complete pellet disintegration and active dispersion occurred within 2.5 minutes at ambient temperature (25 ± 2°C). / Dissertation (MSc)--University of Pretoria, 2008. / Chemistry / unrestricted
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Herstellung SiO2-basierter nano- und mikroskaliger Strukturen via UV-Nanoimprintlithographie auf Basis hybridpolymerer Sol-Gel-Materialien / Synthesis of sio2-based nano- and microscale structures by uv-based nanoimprintlithography based on hybrid sol-gel-materialsBack, Franziska January 2014 (has links) (PDF)
Die vorliegende Arbeit beschreibt die Entwicklung von SiO2-basierten nano- und mikroskalig strukturierten Schichten, welche eine Temperaturstabilität > 500 °C sowie eine Strukturtreue > 90 % aufzeigen. Diese wurden unter Verwendung von hybridpolymeren, partikelmodifizierten Sol-Gel-Vorstufen via UV-basierter Nanoimprintlithographie (UV-NIL) hergestellt. Der Einfluss chemischer und verfahrenstechnischer Syntheseparameter auf die anorganische Netzwerkbildung der flüssigen Vorstufe (hybridpolymerer Binder), die Polymerisation und Verdichtung der hybridpolymeren Sol-Gel-Schichten während der thermischen Härtung sowie deren Strukturierung via UV-NIL wurden im Detail untersucht und die erhaltenen Zusammenhänge mit den resultierenden Materialeigenschaften korreliert. Dabei dienten die Kenntnisse hinsichtlich des Schrumpf- und Verdichtungsverhaltens von planaren Schichten als Basis für die daraus hergestellten, strukturierten Schichten. / The present work describes the development of SiO2-based nano- and microstructured coatings with temperature stability > 500 °C and structure fidelity > 90 %. The coatings were produced via UV-nanoimprintlithography (UV-NIL) by using particle modified, hybrid sol-gel-precursors. The influence of synthesis chemical and process parameters on formation of inorganic network of the hybrid binder, polymerisation and densification of hybrid sol-gel-films during thermal annealing and imprinting of the hybrid sol-gel-films were investigated and correlated with resulting material properties. The results of shrinkage and densification of planar coatings were used to characterize the structured coatings.
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Mechanisms Controlling Ductal Morphogenesis in the Ruminant Mammary GlandEllis, Steven E. 27 October 1998 (has links)
Basic research into the histology, endocrine control, and local regulation of prepuberal ruminant mammogenesis was conducted to provide a better understanding of this important developmental period. Histologic features of prepuberal ruminant mammary parenchymal morphogenesis were examined in tissue samples taken from ewe lambs at 2 (n = 5), 3 (n = 15), 6 (n = 26), 9 (n = 7), 12 (n = 5), and 13 wk (n = 20), and from Holstein heifers at 4 (n = 1) and 6 mo (n = 2). Examination of approximately 8000 histologic sections revealed that mammary parenchymal morphogenesis in sheep and cattle occurs through the proliferation of highly arborescent ductal structures embedded in a dense stroma. These observations contrast strongly with models of mammogenesis based on murine mammary development. The formation of luminal spaces and the expansion of ducts also differed from murine mammogenesis models. Luminal spaces were shown to develop through a progressive separation of opposing sides in initially solid ductal structures. Likewise, our investigation of prepubertal ovine mammogenesis revealed that parenchymal weight, 3H-thymidine labeling, stromal weight, and parenchymal DNA were all unaffected by ovariectomy (P > 0.05), in marked contrast to the dramatic reduction in mammary development following ovariectomy in rats, mice, and heifers. Responsiveness to exogenous estrogen (0.1 mg/kg) was demonstrated by increased 3H-thymidine labeling (P < 0.05) in both intact and ovariectomized lambs. Three dimensional collagen gel cultures of bovine mammary organoids from the peripheral (OUTER) and medial (INNER) parenchymal zones were used to characterize the proliferative and morphogenetic responses to local-acting growth factors. The proliferation of OUTER cells was 2 to 3 times greater than INNER cells (P < 0.0001) in response to IGF-I stimulation. Dramatic differences in the morphology of INNER and OUTER organoids were also observed. INNER cells grew into smooth-edged colonies when treated with heifer serum but stellate colonies when treated with other mitogens. OUTER cells grew into stellate colonies regardless of mitogen treatment. These investigations highlight the fact that a great deal more research into the basic physiology of prepuberal ruminant mammogenesis is required and that dogma developed in murine model systems may not be applicable to ruminant mammary physiology. / Ph. D.
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Bioactivity of sol-gel-derived TiO2 coating on polyetheretherketone: In vitro and in vivo studies / Sol-gel法で酸化チタンコーティングしたPEEK(ポリエーテルエーテルケトン)の生体活性評価Shimizu, Takayoshi 23 March 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20234号 / 医博第4193号 / 新制||医||1019(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 安達 泰治, 教授 横出 正之, 教授 鈴木 茂彦 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM
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Preparation of ribsomal subunits by gel filtrationBhoolia, Deena 20 July 2016 (has links)
A Oiss{!y'tation $uhm'itted in fulfilment
of the r~;~airements, for' the degree of
f·1aster· oi~'j Science at the University
of the ~titwatersrand '
Juhanoasbul"g
January 1991 / An attempt was made to separate ribosomal subunits by gel filtl'ation
on Trisacryl GF2000 and Sepharose 4B. Trisacryl GP~2000,a sYllthet'ic
gol, , separated rat .ljver rlbosonal subunits orl 'f~'135,em column with a
resolution of ""Or3, resulting 'in <'1" 60 rJ impm''ity 'of each of the
\~
subunits.
subunits" were not resolved. Sepharose 4131 an agarose based gol,
separated " the subunits by adsorpttcn chromatography rathr.r than 'i>.V
() Q
':) At 4°C, the 405 .subunf ts were eluted with a kd
()
ruO,:~9( but the GOrf' $ubud"its adsorbed to th~.'g,~Jl and were eluted I;
/)
when the temperature of "the column was increas~d to 250C..3SoC.
(' ,. ('-. This edsorpt ion phenonenon seems to b{~ tl propert~ of a 11 agllrose
-: \') ~\:;
based gels studied here, includ'ing Sepharose 2.B and .seph'ato~eoBt arid
is exc 1us iva to !,mamm'i'lan r ibosOIntrt subuni ts • Anal,ys1S 0'(" the
, u
subunits by in vitro r14C]polypheny1alanine sy'nthes'is showed OCI
" ,,'c. /\ I 7', " diff'erence 'in the act lvtt ies of dbosoma'J ~ubunH~ p~epdrf#d by
;/'/ '
grndient centrifugation or by 5epharos,e cni"OmatogNPPY;' Analy~ii ~~of
"
(~ ((
the subunits by ~crylamidec'ugarose coU)po5it~) gs1s resulted ,in the
'/
resolution ,.:n"f subunits isolated fr'oill lower organisms in
o II
non-denaturlnq !Jcl systems and SI,lbut1its from m«mm~nan'tissue in
II
/'\';1
Ga'! f'iltrat'ion does tyffer a 5t!i:l;~'ble metrKld'¥or the pr~p;n~¥tiol1of
<::) . I \) \\ I)
ribosoma 1 'subunits I but only' if 'the act~orption JH'OrJ&~"t'Jo,s of
,) (,) ':'
o ,1)
,{
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Characterization and Value-Added Utilization of the Proteins Extracted from the By Products of Catfish Fillet Processing PlantGao, Haoran 09 December 2016 (has links)
Proteins in catfish by-products were extracted by two methods: Alkaline extraction (AE) and salt extraction (SE). Properties of the fish protein isolate (FPI) were measured by protein yield and content, moisture content, SDS-PAGE protein patterns, color and texture profile, and compared with commercial surimi products. Our results showed that catfish frame had higher protein yield and color similarity with commercial products than the head; AE-FPI had higher yield and gel strength than SE-FPI; SDS-PAGE protein patterns of FPI from catfish frame by SE method was comparable with commercial surimi products. Based on the results, further optimization of the recovery yield of protein extracted by alkaline extraction method, and effect of microbial transglutaminase (MTGase) on gelation properties under various concentration and reaction time was investigated. Results indicate that the protein yield reached up to 60%, and the addition of MTGase in protein isolate effectively improved the gel forming ability.
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Lichtstreuende Sol-Gel-Schichten für die Si- Dünnschichtphotovoltaik / Light scattering Sol-Gel thin films fo Si thin film solar cellsHegmann, Jan January 2017 (has links) (PDF)
Ziel dieser Arbeit war es, ein Schichtsystem auf Basis des Sol-Gel-Prozesses zu entwickeln, um Lighttrapping in Si-Dünnschichtsolarzellen zu erzeugen. Die Grundlage dieses Schichtsystems bilden SiO2-Partikel, die über den Stöber-Prozess hergestellt werden. Es zeigte sich, dass sich die Rauheit und der Haze der Schichten über die Partikelgröße und Schichtdicke einstellen lassen.
Um die mechanische Stabilität der reinen Stöber-Schichten zu verbessern, kamen verschiedene Binder zum Einsatz. Beste Ergebnisse zeigten Binder basierend auf löslichen Vorstufenpulvern, da diese dem Stöber-Sol beigemischt werden konnten und so Binder und Partikel gleichzeitig aufgebracht werden konnten.
Auf diese Weise entstehen mechanisch stabile, lichtstreuende Schichten. Zum Einsatz kam zunächst ein TiO2-Binder. Durch eine anschließende Glättung der Stöber-TiO2-Streuschichten mit SiO2 entsteht eine defektfreie, aber dennoch raue Oberfläche. Zusätzlich wird ein beträchtlicher Teil des Lichts in große Winkel gestreut.
Es konnte gezeigt werden, dass sich auf den SiO2-geglätteten Stöber-TiO2-Streuschichten ZnO:Al deponieren lässt, wobei die elektrischen Eigenschaften von der Dicke der Glättung abhängen. Auch die elektrischen Eigenschaften der Si-Dünnschichtsolarzellen hängen von der Glättung bzw. der Dicke der Glättung ab. Dies gilt insbesondere für die von der Materialqualität abhängigen Parameter Füllfaktor FF und offen Klemmenspannung VOC. Insgesamt fallen die Parameter jedoch noch gegenüber Referenzzellen auf geätztem Frontkontakt zurück. Vor allem aber wurde die hohe Zellreflexion aufgrund der Glas-TiO2-Grenzfläche als primäres Problem identifiziert. Dennoch konnte bei einer Glättungsdicke von 200 nm sehr gutes Lighttrapping beobachtet werden. Verantwortlich hierfür ist sehr wahrscheinlich die Großwinkelstreuung der Stöber-TiO2-Streuschichten.
Um die Zellreflexion zu verringern, wurde der Brechungsindex des Binders und der Glättungsschichten an den Stack aus Substrat, Streuschicht und ZnO:Al-Schicht angepasst. Idee war es, durch Einbringen eines Al2O3-Vorstufenpulvers eine niedrigbrechende Komponente bereitzustellen, um durch Mischung von Al2O3- und TiO2-Vorstufenpulver freie Hand über den Brechungsindex des Binders und der Glättung zu erhalten.
Da sich das Volumenverhältnis von SiO2-Partikeln zu Binder bei verschiedenen Al2O3-TiO2-Verhältnissen nur schwer bestimmen lässt, wurde lediglich ein reiner Al2O3-Binder in den Streuschichten eingesetzt. Die Einstellung des Brechungsindex beschränkte sich allein auf die Glättungsschichten. Um Stöber-Al2O3-Streuschichten mit hoher Rauigkeit und geringen Defekten zu erzielen, muss das Binder-zu-Partikel-Verhältnis angepasst werden. Beste Ergebnisse ergaben sich bei einem Al2O3-Gehalt von 2% im Sol. Aufgrund der hohen Rauigkeit besitzen die Streuschichten einen hohen Haze und wegen des geringen Brechungsunterschied zwischen Glas und Binder eine hohe Transmission. Die Glättung der Streuschichten im Al2O3-TiO2-System ist nur mit Hilfe einer zusätzlichen SiO2-Glättungsschicht und einer reduzierten Dicke auf 50 nm möglich. Auf den reinen defektreichen Streuschichten tendieren die Al2O3-TiO2-Schichten selbst zu Rissbildung.
Zur Untersuchung der ZnO:Al-Deposition wurde eine Glättungsdicke von 200 nm gewählt. Die erwies sich als zu gering. Die aufgebrachten ZnO:Al-Schichten wiesen größere Poren und kleinere Oberflächendefekte auf. Die Anpassung des Brechungsindex der Glättungsschichten an die ZnO:Al-Schicht erwies sich nicht als vorteilhaft. Die reine Al2O3-Glättung zeigt auch nach der ZnO:Al-Deposition die höchste Transmission. Die Winkelverteilung des Streulichts der Stöber-Al2O3-Streuschichten ist gegenüber den Stöber-TiO2-Streuschichten zu kleineren Winkeln verschoben. Dennoch wird ein größerer Anteil des Lichts in große Winkel gestreut, als es bei der geätzten ZnO:Al-Referenz der Fall ist.
Trotz der Defekte in den ZnO:Al-Schichten konnten auf den Stöber-Al2O3-Streuschichten funktionierende Tandemzellen hergestellt werden. Der Füllfaktor und die offene Klemmenspannung fallen nur geringfügig hinter die der Referenzzelle zurück. In der Kurzschlussstromdichte machen sich die verringerte Zellreflexion und das sehr gute Lighttrapping bemerkbar, so dass das Niveau der Referenz erreicht werden konnte. Zu beachten ist allerdings, dass gerade im langwelligen Lighttrapping-Spektralbereich die gleiche EQE erreicht wurde, trotz immer noch leicht erhöhter Zellreflexion.
Die letzte Versuchsreihe konnte zeigen, dass die entwickelten Schichten sich sehr gut zur Erzeugung von Lighttrapping in Si-Dünnschichtsolarzellen eignen. / The aim of this thesis was to develop a coating system based on the sol-gel process to generate light trapping in Si thin film solar cells. The foundation of this coating system are SiO2 particles which are produced by the Stöber process. The roughness and the haze of the layers can be adjusted by means of the particle size and layer thickness.
To improve the mechanical stability of the pure Stöber layers different binders were used. The best results were found in binders based on soluble precursor powders, as they could be mixed with the Stöber sol so that binders and particles could be applied simultaneously.
This results in mechanically stable, light-scattering layers. Initially, a TiO2 binder was used. A subsequent smoothing of the Stöber-TiO2 scattering layers with SiO2 results in a defect-free but nevertheless rough surface. In addition, a considerable part of the light is scattered in large angles.
It was shown that ZnO: Al can be deposited on the SiO2 -smoothed Stöber-TiO2 scattering layers, the electrical properties depending on the thickness of the smoothing. The electrical properties of the Si thin-film solar cells also depend on the smoothing or the thickness of the smoothing. This is especially true for the material quality dependent parameters fillfactor FF and open circuit voltage Voc. Overall, however, the parameters still fall short of reference cells on etched front contact. Most importantly, the high cell reflectance was identified as the primary problem due to the glass-TiO2 interface. Nevertheless, very good light trapping could be observed with a smoothing thickness of 200 nm. This is most likely due to the large-angle scattering of the Stöber-TiO2 scattering layers.
In order to reduce the cell reflection, attempts have been made to adapt the refractive index of the binder and the smoothing layers to the stack of substrate, scattering layer and ZnO:Al. The idea was to provide a low refractive component by adding an Al2O3 precursor powder in order to obtain full control on the refractive index of the binder and the smoothing by mixing Al2O3 and TiO2 precursor powders. Since the volume ratio of SiO2 particles to binders is difficult to determine at different Al2O3-TiO2 ratios , only a pure Al2O3 binder was used in the scattering layers. The adjustment of the refractive index was limited solely to the smoothing layers. To achieve Stöber-Al2O3 scattering layers with high roughness and low defects, the binder-to-particle ratio must be adjusted. The best results were obtained with an Al2O3 content of 2% in the sol. Due to the high roughness, the scattering layers have a high Haze and a high transmission because of the small difference in refraction index between glass and binder. The smoothing of the scattering layers in the Al2O3-TiO2 system is only possible with the aid of an additional SiO2 smoothing layer and a reduced thickness to 50 nm . On the pure defect-rich scatttering layers, the Al2O3 -TiO2 layers themselves tend to crack.
To investigate the ZnO:Al deposition, a smoothing thickness of 200 nm was chosen. That turned out to be too low . The applied ZnO:Al layers had larger pores and smaller surface defects. The adjustment of the refractive index of the smoothing layers to the ZnO:Al layer did not prove to be advantageous. The pure Al2O3 smoothing shows the highest transmission even after the ZnO:Al deposition. The angular distribution of the scattered light of the Stöber-Al2O3 scattering layers is shifted towards smaller angles than the Stöber-TiO2 scattering layers. Nevertheless, a larger fraction of the light is scattered into large angles than is the case with the etched ZnO:Al reference.
Despite the defects in the ZnO:Al layers , functional tandem cells could be prepared on the Stöber- Al2O3 scattering layers. The fill factor and the open circuit voltage fall only slightly behind those of the reference cell. The short-circuit current density, the reduced cell reflection and the very good light trapping are noticeable, so that the level of the reference could be reached. It should be noted, however, that the same EQE was achieved in the long-wavelength light trapping spectral range, despite the still slightly increased cell reflection.
The last series of experiments showed that the developed layers are very well suited for the generation of light trapping in Si thin-film solar cells.
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