Thesis describes recent advances in the synthesis of donor-acceptor conjugated copolymers and their efficient doping via molecular p-dopants.

Thesis describes recent advances in the synthesis of donor-acceptor conjugated copolymers and their efficient doping via molecular p-dopants.:Chapter I Preface Motivation and Goals Outline 7 Chapter II 8 State of the Art & Characterization Techniques 8 2.1. General Introduction 8 2.1.1. Concept of Conjugated Polymers 9 2.1.2. Electronic Conduction and Necessity of Doping in Conjugated Polymers 11 2.1.3. Solubility and Processing. 14 2.2. Doping 17 2.2.1. Concept of Doping in Conjugated Polymers 17 2.2.2. Morphological Changes of the Material upon Doping. Conductivity. 20 2.2.3. State-of-the-art p-dopants. 23 2.3. Synthetic Strategies for the Design of (Semi)conducting Polymers 28 2.3.1. A Concise Review: from Polyacetylene till Modern DA Polymers 28 2.3.2. Synthetic Routes to Conjugated Polymers 31 2.3.3. Step-growth vs Chain-growth 34 2.3.4. Benchmark solution-processable Polymers 38 2.4. Characterization techniques 41 2.4.1. Conductivity Measurements 41 2.4.2. Electrochemical Voltammetry 42 2.4.3. Uv-vis-near-infrared 44 2.4.4. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. 44 2.4.5. Morphological studies. 45 2.4.6. Electron Spin Resonance Spectroscopy. 46 Chapter III 48 Results & Discussion 48 3.1. Diketopyrrolopyrrole-Based Copolymers 50 3.1.1. Motivation 50 3.1.2. Results and Discussion 51 3.1.4. Summary 89 3.2. Naphthalene Diimide-based Copolymer 90 3.2.1. Motivation 90 3.2.2. Results and Discussion 92 3.2.4. Summary 105 3.3. Isoindigo-Based Copolymers 107 3.3.1. Motivation 107 3.3.2. Results and Discussion 108 3.3.4. Summary 119 Summary & Conclusions 120 Outlook 123 Chapter IV 125 Experimental Part 125 4.1. General Methods and Instrumentation 125 4.2. Synthesis 129 4.2.1. Synthesis of diketopyrrolopyrrole copolymer. 129 4.2.2. Synthesis of electron-conducting polymer (PNDIT2) 132 4.2.3. Synthesis of polyisoIndigo 132 4.2.3. Synthesis of Dopants 135 4.3. Cyclic voltammetry measurements 136 4.4. GIWAX data. 143 4.5. Films preparation 145 References 147 Table of Abbreviations 159 List of Publications 161 Acknowledgements 162 Appendix 163

As the size of modern transistors is continuously scaled down, challenges rise in almost every component of a silicon device. Formation of ultra shallow junction (USJ) with high activation level is particularly important for suppressing short channel effects. However, the formation of low resistance USJ is made difficult by dopant Transient Enhanced Diffusion (TED) and clustering-induced deactivation. In this work, we proposed a novel point defect engineering solution to address the arsenic TED challenge. By overlapping arsenic doped region with silicon interstitials and vacancies, we observed enhanced and retarded arsenic diffusion upon anneal, respectively. We explain this phenomenon by arsenic interstitial diffusion mechanism. In addition, we implemented this interstitial-based mechanism into a kinetic Monte Carlo (kMC) simulator. The key role of interstitials in arsenic TED is confirmed. And we demonstrated that the simulator has an improved prediction capability for arsenic TED and deactivation. As a long time unsolved process challenge, arsenic segregation at SiO₂/Si interface was investigated using density functional theory (DFT) calculation. The segregation-induced arsenic dose loss not only increases resistance but also may induce interface states. We identified three arsenic complex configurations, [chemical formula] , [chemical formula] and [chemical formula], which are highly stabilized at SiO₂/Si interface due to the unique local bonding environments. Therefore, they could contribute to arsenic segregation as both initial stage precursors and dopant trapping sites. Our calculation indicates that arsenic atoms trapped in such interface complexes are electrically inactive. Finally, the formation and evolution dynamics of these interface arsenic-defect complexes are discussed and kMC models are constructed to describe the segregation effects. A potential problem for the p-type USJ formation is the recently found transient fast boron diffusion during solid phase epitaxial regrowth process. Using DFT calculations and molecular dynamics simulation, we identified an interstitial-based mechanism of fast boron diffusion in amorphous silicon. The activation energy for this diffusion mechanism is in good agreement with experimental results. In addition, this mechanism is consistent with the experimentally reported transient and concentration-dependent features of boron diffusion in amorphous silicon. / text

To ensure that photovoltaics contributes significantly to future world energy production, the cost per watt of producing solar cells needs to be drastically reduced. The use of n-type silicon wafers in conjunction with industrial print technology has the potential to lower the cost per watt of solar cells. The use of n-type silicon is expected to allow the use of cheaper Cz substrates, without a corresponding loss in device efficiency. Printed metallisation is well utilised by the PV industry due to its low cost, yet there are few examples of its application to n-type solar cells. This thesis explores the use of n-type Cz silicon with printed metallisation and diffusion from printed sources in creating industrially applicable solar cell structures. The thesis begins with an overview of existing n-type solar cell structures, previous printed thick film metallisation research and previous research into printed dopant sources. A study of printed thick-film metallisation for n-type solar cells is then presented, which details the fabrication of boron doped p-type emitters followed by a survey of thick film Ag, Al, and Ag/Al inks for making contact to a p-emitter layer. Drawbacks of the various inks include high contact resistance, low metal conductivity or both. A cofire regime for front and rear contacts is established and an optimal emitter selected. A study of printed dopant pastes is presented, with an objective to achieve selective, heavily doped regions under metal contacts without significantly compromising minority carrier lifetime in solar cells. It is found that heavily doped regions are achievable with both boron and phosphorus, but that only phosphorus paste was capable of post-processing lifetime compatible with good efficiencies. The effect of belt furnace processing on n-type silicon wafers is explored, with large losses in implied voltage observed due to contamination of Si wafers from transition metals present in the belt furnace. Due to exposure to chromium in the belt furnace, no significant advantage in using n-type wafers instead of p-type is observed during the belt furnace processing step. Finally, working solar cells with efficiencies up to 16.1% are fabricated utilising knowledge acquired in the earlier chapters. The solar cells are characterised using several new photoluminescence techniques, including photoluminescence with current extraction to measure the quality of metal contacts. The work in this thesis indicates that n-type printed silicon solar cell technology shows potential for good performance at low cost.

En raison de la miniaturisation des dispositifs pour semi-conducteurs, le caractère aléatoire de la distribution de dopants dans un dispositif devient un paramètre critique pour les performances de ce dernier. Le but de ce travail est de valider une stratégie de dopage du silicium par un positionnement contrôlé de molécules, alternatif aux implantations, afin de limiter la variabilité de la tension de seuil. Nous avons choisi de contrôler la densité des sites et le positionnement des dopants en combinant le contrôle de la densité des sites d'ancrage et l'utilisation de molécules à fort encombrement stérique. Ceci a été réalisé en étudiant dans un premier temps le greffage de bore sur les silanols de silice amorphe partiellement traitée en température, à partir de molécules porteuses présentant des ligands de différentes tailles et des symétries ; le modèle de greffage a pu être déterminé en utilisant différentes techniques analytiques (IR-DRIFT, multi-core SSRMN et analyses élémentaires). L'élimination des ligands par un traitement thermique a permis de réaliser la fixation du Bore sur la silice avec un rendement supérieur à 96%. Cette méthode a été transférée avec succès à des wafers de silicium recouverts de silice native. Le recuit à haute température permettant la redistribution du bore dans le silicium a été ensuite validée par l'analyse VPD-ICPMS de l'oxyde greffé couplées aux mesures de profil de dopant dans le silicium obtenues par TofSIMS. Ce traitement a conduit à définir un procédé optimal par greffage sur silice mince, donnant des concentrations de dopant dans le silicium équivalentes à celles rapportées par la littérature sur silicium désoxydé, et sans passivation additionnelle de silice pour éviter la volatilisation du Bore greffé. En effet, la taille des ligands permet de contrôler la volatilisation du bore pendant recuit. Les analyses électriques par spectroscopie à effet tunnel ont confirmé l'activation électrique du dopant apporté par greffage et diffusé dans le silicium

No description available.

To ensure that photovoltaics contributes significantly to future world energy production, the cost per watt of producing solar cells needs to be drastically reduced. The use of n-type silicon wafers in conjunction with industrial print technology has the potential to lower the cost per watt of solar cells. The use of n-type silicon is expected to allow the use of cheaper Cz substrates, without a corresponding loss in device efficiency. Printed metallisation is well utilised by the PV industry due to its low cost, yet there are few examples of its application to n-type solar cells. This thesis explores the use of n-type Cz silicon with printed metallisation and diffusion from printed sources in creating industrially applicable solar cell structures. The thesis begins with an overview of existing n-type solar cell structures, previous printed thick film metallisation research and previous research into printed dopant sources. A study of printed thick-film metallisation for n-type solar cells is then presented, which details the fabrication of boron doped p-type emitters followed by a survey of thick film Ag, Al, and Ag/Al inks for making contact to a p-emitter layer. Drawbacks of the various inks include high contact resistance, low metal conductivity or both. A cofire regime for front and rear contacts is established and an optimal emitter selected. A study of printed dopant pastes is presented, with an objective to achieve selective, heavily doped regions under metal contacts without significantly compromising minority carrier lifetime in solar cells. It is found that heavily doped regions are achievable with both boron and phosphorus, but that only phosphorus paste was capable of post-processing lifetime compatible with good efficiencies. The effect of belt furnace processing on n-type silicon wafers is explored, with large losses in implied voltage observed due to contamination of Si wafers from transition metals present in the belt furnace. Due to exposure to chromium in the belt furnace, no significant advantage in using n-type wafers instead of p-type is observed during the belt furnace processing step. Finally, working solar cells with efficiencies up to 16.1% are fabricated utilising knowledge acquired in the earlier chapters. The solar cells are characterised using several new photoluminescence techniques, including photoluminescence with current extraction to measure the quality of metal contacts. The work in this thesis indicates that n-type printed silicon solar cell technology shows potential for good performance at low cost.

abstract: In very small electronic devices the alternate capture and emission of carriers at an individual defect site located at the interface of Si:SiO2 of a MOSFET generates discrete switching in the device conductance referred to as a random telegraph signal (RTS) or random telegraph noise (RTN). In this research work, the integration of random defects positioned across the channel at the Si:SiO2 interface from source end to the drain end in the presence of different random dopant distributions are used to conduct Ensemble Monte-Carlo ( EMC ) based numerical simulation of key device performance metrics for 45 nm gate length MOSFET device. The two main performance parameters that affect RTS based reliability measurements are percentage change in threshold voltage and percentage change in drain current fluctuation in the saturation region. It has been observed as a result of the simulation that changes in both and values moderately decrease as the defect position is gradually moved from source end to the drain end of the channel. Precise analytical device physics based model needs to be developed to explain and assess the EMC simulation based higher VT fluctuations as experienced for trap positions at the source side. A new analytical model has been developed that simultaneously takes account of dopant number variations in the channel and depletion region underneath and carrier mobility fluctuations resulting from fluctuations in surface potential barriers. Comparisons of this new analytical model along with existing analytical models are shown to correlate with 3D EMC simulation based model for assessment of VT fluctuations percentage induced by a single interface trap. With scaling of devices beyond 32 nm node, halo doping at the source and drain are routinely incorporated to combat the threshold voltage roll-off that takes place with effective channel length reduction. As a final study on this regard, 3D EMC simulation method based computations of threshold voltage fluctuations have been performed for varying source and drain halo pocket length to illustrate the threshold voltage fluctuations related reliability problems that have been aggravated by trap positions near the source at the interface compared to conventional 45 nm MOSFET. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011

Submitted by Lucas Fabricio Gonçalves (trippa07@gmail.com) on 2018-09-21T20:19:52Z No. of bitstreams: 1 Tese Lucas Fabricio Gonçalves final.pdf: 5953100 bytes, checksum: 5575be8c51df4743f9dc5776305df382 (MD5) / Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2018-09-21T20:31:22Z (GMT) No. of bitstreams: 1 gonçalves_lf_dr_guara.pdf: 5953100 bytes, checksum: 5575be8c51df4743f9dc5776305df382 (MD5) / Made available in DSpace on 2018-09-21T20:31:22Z (GMT). No. of bitstreams: 1 gonçalves_lf_dr_guara.pdf: 5953100 bytes, checksum: 5575be8c51df4743f9dc5776305df382 (MD5) Previous issue date: 2018-07-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os elementos de memórias de múltiplos estados nos quais a informação pode ser armazenada tanto nos estados de polarização quanto no estado de magnetização espontânea do elemento, podem ser obtidos, através da fabricação de filmes finos texturizados de BiFeO3 (BFO) dopados com Cálcio, sobre eletrodo de (Pt/TiO2/SiO2/Si), visando otimizar as propriedades ferroeletromagnêticas. O método Pechini ou percursores poliméricos, depositados por “Spin-Coating”, é relativamente de fácil controle e baixo custo para a deposição de filmes finos texturizados. O cristal do BiFeO3 possui uma estrutura perovskita distorcida em um sistema romboédrica , mas em formato de filme fino encontramos uma fase pseudo tetragonal favorável as propriedades de memorias de múltiplos estados, como a diminuição da degradação, aumento da polarização espontânea e remanescente, diminuição na corrente de fuga, diminuição do tempo de resposta ao impulso, crescimento epitaxial, controle de vacâncias de oxigênio e diminuição de fases secundarias. Tudo isso é atingido, através de variações das resinas, controlando a volatização excessiva do Bismuto e de parâmetros no crescimento do filme, como, o tempo e temperatura de cristalização, da quantidade de dopante Ca, na variação de diferentes eletrodos óxidos de base para produção do filme fino. Apesar das excelentes propriedades dos filmes finos de BiFeO3 (BFO), dois sérios problemas são comumente encontrados para imediata aplicação deste material em memórias multiferróicas: alta densidade de corrente, resultado da flutuação de valência dos íons Fe (Fe3+ para Fe2+) com consequente criação de vacâncias de oxigênios, da existência de fases secundárias e elevado campo coercitivo causado pelo grande número de contornos de grãos, que restringe a reversão da polarização. Uma transição condutor-isolante foi observada pela dopagem do BFO com Ca devido ao completo preenchimento dos níveis de fermi levando a uma transição ferroelétrico-antiferromagnético. Além disso, o uso do cálcio como dopante (x = 0,30) melhora as propriedades ferroelétricas dos filmes de BFO pois: reduz a resistência a fadiga, a retenção de dados e o campo coercitivo do filme suprimindo a volatilização de óxido de bismuto e a presença de vacâncias de oxigênio. A cristalização de filmes em eletrodos condutores de LSCO, no forno de microondas conduziu a uma excelente resposta piezoelétrica, quando comparada aos eletrodos de LaNiO3 devido à restrição das cargas espaciais para interface filme-substrato. / The multi-state memory elements in which the information can be stored in both the polarization states and the spontaneous magnetization state of the element can be obtained by the production of calcium-doped thin films of BiFeO3 (BFO) on electrode (Pt / TiO2 / SiO2 / Si), in order to optimize ferroelectromagnetic properties. The Pechini method or polymer precursors, deposited by Spin-Coating, is relatively easy to control and low cost for the deposition of textured thin films. The crystal of the BiFeO3 has a perovskite structure distorted in a rhombohedral system, but in thin film format we find a pseudo tetragonal phase favorable to the properties of memories of multiple states, such as the decrease of the degradation, increase of the spontaneous and remaining polarization, decrease in the current reduction of impulse response time, epitaxial growth, control of oxygen vacancies and decrease of secondary phases. All of this is achieved through variations of the resins, controlling the excessive volatilization of Bismuth and parameters in the growth of the film, such as the time and temperature of crystallization, the amount of dopant Ca, in the variation of different base oxides electrodes for production of the thin film. Despite the excellent properties of the BiFeO3 (BFO) thin films, two serious problems are commonly encountered for the immediate application of this material in multiferroic memories: high current density, resulting in Fe (Fe3 + to Fe2 +) valence fluctuation with consequent oxygen vacancies, the existence of secondary phases and a high coercive field caused by the large number of grain contours, which restricts the reversal of polarization. A conductor-insulate transition was observed by the BFO doping with Ca due to the complete filling of the fermi levels leading to a ferroelectric-antiferromagnetic transition. In addition, the use of calcium as a dopant (x = 0.30) improves the ferroelectric properties of BFO films because: it reduces fatigue endurance, data retention and the coercive field of the film by suppressing bismuth oxide volatilization and the presence of oxygen vacancies. In contrast, leads to a low piezoelectric signal, by reducing the remaining polarization along the a-axis, in which the piezoelectric properties are quite pronounced. The crystallization of films on LSCO conductive electrodes in the microwave oven led to an excellent piezoelectric response image when compared to the LaNiO3 electrodes due the inhibition of space charges migration to the film-substrate interface

This thesis concentrates on the methodology of semiconductor samples preparation for low voltage scanning electron microscopy. In the first part a detailed theory of sample imaging using electron beam and difference between classical scanning electron microscopy (SEM) and low voltage scanning electron microscopy (LVSEM) is described. It is given a description of a contrast formation in SEM and LVSEM and theories describing a contrast formation of differently doped semiconductors. The second part contains experimental data. The advantages and disadvantages of cleavage and focused ion beam (FIB) milling as sample preparation techniques are discussed. FIB was found as the best method for sample preparation for the analysis of precisely defined location on the sample. It is necessary to use the lowest possible FIB accelerating voltage for final polishing, ideally 1 kV.