The goal of this research was to utilize the morphological control inherently imparted by the electrospinning process to improve the active layer performance in energy conversion devices as well as to better understand the relationship between morphology and performance in energy storage devices. Discrete control of the active layer morphology can promote exciton dissociation in organic photovoltaic cells (OPVs), whereas developing efficient ion diffusion pathways and beneficial polymer-ion interaction in polymer-gel electrolytes is demonstrated to result in enhanced battery performance. We demonstrate the ability to develop unique morphologies in Poly(3-hexafluoro propylene) (P3HT) films with energy storage applications using various electrospinning techniques. Electrospinning in a solvent-saturated atmosphere allows for the design of ribbon architectures with polymer domains on the order of 5-10 um. These ribbon structures form what appear to be bi-continuous films, which could then be filled with an acceptor / fullerene type material to create a bulk heterojucton for OPV devices. Dropping chloroform onto the electrospinning needle during the spinning process results in P3HT fibers with porous surfaces. These fibers have diameters of ~ 2 um. Using a coaxial needle to electrospin a P3HT solution in the core, and a CHCl3 sheath solution created hybrid ribbon-fiber structures. These structures have even smaller domain sizes than the ribbons created using a solvent saturated atmosphere. Cospinning P3HT with sacrificial polymers results in P3HT fiber morphologies upon removal of the sacrificial template polymer. Additionally, introducing P3HT into an established fiber matrix results in fibrous P3HT architectures after the template fibers are removed. Developing hybrid polymer-gel electrolytes using crosslinked PEO electrospun fibers results in membranes with high affinity for liquid electrolyte components. These electrospun PEO fiber mats exhibit excellent ionic conductivities at room temperature (12 mS/cm) exceeding an electrospun PVDF control. Furthermore, the PEO fiber mats can absorb nearly three times as much liquid electrolyte as the PVDF control. PEO has been show to interact with lithium salts to aid in dissociation and diffusion during battery cycling. Although the ionic conductivity data suggest PEO to be a superior electrolyte, pulsed-field-gradient NMR shows that lithium diffusion is faster in PVDF samples. From coin cell discharge experiments, PEO is believed to interact strongly with Li+ ions, inhibiting them from diffusing rapidly during fast charge/discharge rates. However, PEO/PETA fiber electrolytes show nearly 100% theoretical capacity discharge at C/100 and a capacity retention of ~ 35% at a C/5 discharge rate in contrast to a glass fiber separator which shows only a capacity that is approximately 85% of the theoretical value. The unique mechanical properties of PEO/PETA electrospun mats could lead to interesting artificial skin and wound healing applications. Upon crosslinking at elevated temperatures (~40 degrees C), the fiber mats exhibit improved tensile strength and much higher ultimate stress at break. The porous nature of the materials lend to easy oxygen diffusion for wound healing, and the hydrophilicity promotes continued adhesion to existing tissue making these mats possible adhesive-less bandages. / Ph. D.

The proposed research is for a novel SiGe-based Ion-Sensitive Dual Hetero-junction Bipolar Transistor (IS-HBT) to be used in both trans-dermal biological sensing as well as Lab-on-Chip (LOC) applications. The end goals for the device designed are two: For one, the research done for this work will be used to substantiate the claims made by Zafar et al. [1] that an HBT-style structure is better suited for biosensing application rather than a conventional Field Effect Transistor (FET) based geometries. Secondly, it provides the final element to be integrated along with a selectivity membrane, as well as with a reverse-iontophoresis system to enact trans-dermal sensing of potassium ions in a wearer’s body. The novelty of the device stems from the proposed modified wedding-cake structure lending itself to be easily implemented in a wearable package, the fact that it will act as both a transduction device as well as provide preamplification of signals. If successful, future researchers and/or corporations will have at their disposal a label-free advanced biosensor design that is integration-ready with currently available standard SiGe-BiCMOS processes.

In this work, we have explored 2D semiconducting transition metal dichalcogenides (TMDs), black phosphorus (BP), and graphene for various applications using liquid and mechanical exfoliation routes. The topical areas of interest that motivate our work include considering factors such as device integration, stability, doping, and the effect of gasses to modulate the electronic transport characteristics of the underlying 2D materials. In the first area, we have integrated solution-processed transparent conducting oxides (TCOs), specifically indium-doped tin oxide (ITO) with BP, which is a commonly used TCO for solar cell devices. Here we have found surface treatment of glass substrates with a plasma before spin-coating the solution-processed ITO, to be effective in improving coverage and uniformity of the ITO film by promoting wettability and film adhesion. The maximum transmittance obtained was measured to be ~75% in the visible region, while electrical measurements made on BP/ITO heterostructures showed improved transport characteristics compared to the bare ITO film. Within the integration realm, inkjet-printing of BP and MoS2 p-n hetero-junctions on standard ITO glass substrates in a vertical architecture was also demonstrated. To address the issue of stability which some 2D materials such as BP face, we experimented with ionic liquids (ILs) to passivation the hydrophilic surface of BP to minimize its oxidative degradation. The enhanced stability of BP was inferred through Raman spectroscopy and scanning probe microscopy techniques, where no observable changes in the A1g and A2g Raman vibrational modes were observed for the BP films passivated with ILs over time under ambient conditions. On the other hand, a blue-shift in these Raman modes was evident for unpassivated samples. Atomic force microscopy measurements on the unpassivated samples clearly revealed the difference in surface characteristics through localized regions of degradation that intensified with time which was absent in IL passivated BP samples. The electronic device measurements for IL coated BP devices showed a more stabilized Ids−Vds characteristic in the 5.4 K to 335 K temperature range. Prototypical demonstrations of stabilized ILs/BP devices at ambient printed on flexible polyimide substrates were also successfully made. At the same time, doping is one of the essential steps required for the modulation of carrier density and electronic transport in electronic and optoelectronic devices, which is the third topical area we have addressed in this work with semiconducting TMDs. Of the conventional approaches used to dope 3D semiconductors, ion-implantation is commonly adopted but given the ultra-thin nature of 2D materials, this approach is not feasible as it causes severe damage to the delicate crystalline lattice of ultra-thin 2D membranes. Instead, we have used plasma-based doping routes with UV-ozone treatement and solution processing using 1,2 dichloroethane, to characterize the temperature-dependent two-terminal and three-terminal electronic and optoelectronic transport of mechanically exfoliated 2D MoS2 and WSe2. A significant difference was seen in the optoelectronic properties between the two dopants, owing to differences in their respective doping mechanisms and the intrinsic structural attributes of the exfoliated flakes. A significant reduction in barrier height was evident after doping using both techniques in MoS2, while an increase in barrier height after soaking in 1,2 dichloroethane was seen in WSe2. Lastly, in the fourth topical area for sensing devices, we have studied the effect of gas-flow in inkjet-printed and spin-coated graphene and MoS2 to modulate the electronic transport for the 2D materials since their increased surface area is an ideal platform to observe interactions with external stimuli, in this case, in-coming gas species. Here, the chamber pressure and change in current with flow of gas was measured in the steady-state, as well as time-dependent dynamic transport toward nitrogen and carbon dioxide. We observed significant differences in the electrical response of mono-elemental graphene and binary MoS2, owing to differences in microstructure and joule heating response to the ambient gas. In conclusion, the findings obtained from our work will provide an important framework to help guide strategies in further improving integration schemes, stability, doping and sensing behavior driven by the unique structural attributes inherent to 2D materials for high-performance devices in the future.

This thesis investigates novel hole extraction interfaces and series interconnects for applications in organic photovoltaics, specifically in single junction solid-state dye-sensitized solar cells (DSSCs) and tandem DSSC/polymer bulk heterojunction solar cells. Improvements in hole extraction and device performance by using materials compatible with scalable deposition methods are presented, including tungsten- and molybdenum-disulphide (WS₂ and MoS₂), and p-type doped spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) nanoparticle dispersions. WS₂ and MoS₂ hole extraction layers increase averaged short circuit currents by 20% and 16% respectively, and power conversion efficiencies by 19% and 14% respectively when compared with control devices. Similarly, doped spiro-OMeTAD nano-particle layers improved short circuit current densities by 32% and efficiencies by 9%. Tandem device interconnects using these novel hole extraction formats have been fabricated, but although devices did exhibit rectification, overall performance was poor. Possible reasons for their limited success have been analysed. Dye-sensitized solar mini-modules are also reported. In order to assure the scalability of DSSC technology, these larger area devices were constructed using doctor blade coating to deposit the hole transporter material. As well as achieving a respectable maximum power conversion efficiency of 2.6%, it has also been shown that the extent to which hole transporter infiltrates the mesoporous photoanode of these devices may be tuned by altering substrate temperature during deposition. It was found that an optimal coating temperature of 70 degrees C produced the best efficiency, with a corresponding pore-filling fraction of 41%.

Les hétérojonctions formées de deux matériaux, un donneur et un accepteur (D/A), sont la base de la majorité des mélanges photovoltaïques organiques. Les mécanismes de séparation des charges dans ces systèmes représentent aujourd'hui l'un des sujets les plus chauds et les plus débattus dans ce domaine. Nous entrons au coeur de ce débat en choisissant un système D/A à base de phtalocyanine de cuivre (CuPc) et de fullerène (C60). Pour sonder les états excités de nos molécules et obtenir de l'information sur les phénomènes à l'interface D/A, nous réalisons une expérience pompe-sonde, appelée absorption photoinduite (PIA). Nous y mesurons le changement fractionnaire de transmission au travers de l'échantillon. Les mesures de PIA sont réalisées à l'état de quasi équilibre, à T=10K. Nous observons une modulation prononcée dans la région du photoblanchiment de l'état fondamental qui nous indique que la pompe induit un décalage du spectre d'absorption de l'état fondamental. Ce décalage peut être expliqué par deux processus : soit l'échantillon est chauffé par la pompe (effet thermique) ou bien des charges sont créées à l'interface entre les deux matériaux (effet Stark). La dépendance en température du spectre d'absorption entre 10K et 290K montre une signature thermique pour un changement de température de 80K. Grâce au ratio des raies Raman anti-Stokes et Stokes, nous démontrons que la pompe chauffe l'échantillon de 34 K, température insuffisante pour attribuer notre signal à un effet thermique. Nous évaporons ensuite la bicouche CuPc/C60 sur de l'ITO et du saphir, substrats qui possèdent des conductivités thermiques différentes et nous observons le même signal de PIA, excluant par le fait même l'hypothèse de l'effet thermique. Puisque notre étude est comparable à la spectroscopie à effet Stark, nous procédons à une analyse similaire en comparant notre signal de PIA au spectre de la transmittance et à ses dérivés première et seconde. Nous observons alors que notre signal reproduit presque parfaitement la dérivée seconde de la transmittance. Ces résultats sont conformes à une signature optique d'effet Stark due à la création de charges à l'interface D/A. / Nowadays, the donor/acceptor (D/A) structure is one of the most popular configuration for organic solar cells. The charge separation mechanisms in this type of systems is now a hot topic of debate in this field of research. To adress this debate, we choose a D/A system made of copper phthalocyanine (CuPc) and fullerene (C60). In this work, we perform quasi-steady-state photoinduced absorption (PIA) measurements which consist of a pump-probe experiment where we measure the fractional change in transmission through the sample. This experiment probes the excited states of our molecules and gives us informations about the photophysics near the interface between the two materials. The measurements were mainly done at T=10K. We observe a strong modulation of the ground state photobleaching that indicates that the laser excitation induces a shift of the ground state absorption spectrum. This shift can be ascribed to two processes: either the pump is heating the sample (heat transfer) or charge are being created at the interface between the two materials (Stark effect). The temperature dependence of the absorption spectrum between T=10K and T=290K shows a thermal signature for a change in temperature of 80K. By calculating the ratio of the Raman Stokes and anti-Stokes peaks, we establish that the pump heat up the sample of 34K, an insufficient temperature to assign the change of transmittance to a thermal effect. We then evaporate our CuPc/C60 bilayer on ITO and sapphire, two substrates with different thermal conductivities and we observe the same signal thereby excluding the assumption of the thermal effect. Since our study bears a resemblance to Stark spectroscopy, we justify the use of a similar analysis by comparing our PIA signal to the transmittance spectrum of our molecules and its first and second derivative. We find that the signal reproduces almost perfectly the second derivative. Thus, we attribute the aforementioned results to an optical signature of Stark effect due to the creation of charges at the heterojunction.

Graphene base transistors (GBTs) have been, recently, proposed to overcome the intrinsic limitations of the graphene field effect transistors (GFETs) and exploit the graphene unique properties in high frequency (HF) applications. These devices utilize single layer graphene as the base material in the vertical hot-electron transistors. In an optimized GBT, the ultimate thinness of the graphene-base and its high conductivity, potentially, enable HF performance up to the THz region.  This thesis presents an experimental investigation on the GBTs as well as integration process developments for the fabrication of graphene-based devices. In this work, a full device fabrication and graphene integration process were designed with high CMOS compatibility considerations. To this aim, basic process modules, such as graphene transfer, deposition of materials on graphene, and formation of tunnel barriers, were developed and optimized. A PDMS-supporting graphene transfer process were introduced to facilitate the wet/dry wafer-scale transfer from metal substrate onto an arbitrarily substrate. In addition, dielectric deposition on graphene using atomic layer deposition (ALD) was investigated. These dielectric layers, mainly, served as the base-collector insulators in the fabricated GBTs. Moreover, the integration of silicon (Si) on the graphene surface was studied. Using the developed fabrication process, the first proof of concept devices were demonstrated. These devices utilized 5 nm-thick silicon oxide (SiO2) and about 20 nm-thick aluminum oxide (Al2O3) as the emitter-base insulator (EBI) and base-collector insulator (BCI). The direct current (DC) functionality of these devices exhibited &gt;104 on/off current ratios and a current transfer ratio of about 6%. The performance of these devices was limited by the non-optimized barrier parameters and device manufacturing technology. The possibility to improve and optimize the GBT performance was demonstrated by applying different barrier optimization approaches. Comparing to the proof of concept devices, several orders of magnitude higher injection current density was achieved using a bilayer dielectric tunnel barrier. Utilizing the novel TmSiO/TiO2 (1 nm/6 nm) dielectric stack, this tunnel barrier prevents defect mediated tunneling and, simultaneously, promotes the Fowler-Nordheim tunneling (FNT) and step tunneling (ST). Furthermore, it was shown that Si/graphene Schottky junction can significantly improve the current gain by reducing the electron backscattering at the base-collector barrier. In this thesis, a maximum current transfer ratio of about 35% has been achieved. / <p>QC 20160503</p>

As aplicações dos dispositivos conversores de energia luminosa, principalmente da luz solar, em energia elétrica são muito variadas e com freqüência surge a possibilidade de uma nova aplicação. Muito tem sido discutido sobre aplicações de células solares em vestimentas, mochilas, tetos de estacionamentos e em embalagens eletrônicas. Esses tipos de aplicações não exigem dispositivos de alto desempenho, porém exigem que seja de baixo custo de processamento e, principalmente, que sejam flexíveis. Dispositivos fotovoltaicos flexíveis devem então ser fabricados por técnicas simples de processamento para permitir sua eventual produção em massa. Esse trabalho pretende dar uma contribuição na escolha dos materiais a serem usados em dispositivos fotovoltaicos flexíveis, focando seu desenvolvimento em células solares orgânicas de heterojunção de volume (BHJ), que são comumente processadas por solução. A estrutura escolhida foi a convencional de multicamadas onde o anodo transparente é o ITO (óxido de índio-estanho), seguida de uma camada transportadora de buracos (PEDOT:PSS), da camada ativa, e do cátodo, que em nosso caso foi formado por cálcio e alumínio, ambos depositados a vácuo. Como camada ativa, principal elemento de estudo nesse trabalho, foram estudados o P3HT:PC61BM, e o PTB7-Th:PC71BM, como elementos doador de elétrons (polímero) e aceitador de elétrons (derivado de fulereno). Em especial com o dispositivo fabricado com o PTB7-Th:PC71BM foi possível elaborar mudanças de processamento e assim melhorar consideravelmente a sua eficiência de conversão de potência. Em seguida, através de medidas de corrente-tensão (J-V) no escuro e sob iluminação, pudemos analisar a evolução dos parâmetros das células, como as resistências série (Rs) e paralelo (Rp), e também aqueles que definem a qualidade da célula solar: a corrente de curto-circuito (Jsc), a tensão de circuito aberto (Voc), o fator de preenchimento (FF), e a eficiência (&#951;). Através dos ajustes das curvas J-V, no escuro e sob iluminação, usando expressões de J(V) extraídas de circuitos equivalentes, respectivamente, dos diodos e das células solares, pudemos realizar uma análise mais efetiva de como as resistências série e paralelo mudam com os elementos da camada ativa e também com diferentes processamentos. O fator de preenchimento (FF) é outro parâmetro importante que determina a eficiência de conversão de energia de uma célula solar orgânica, e existem vários fatores que podem influenciar significativamente o seu valor. Essa é uma das razões do porquê é difícil identificar a real origem desse parâmetro. Essa tese também deu elementos que correlacionam a estrutura química e morfológica da camada ativa com o fator de preenchimento. / The applications of light energy converters, especially the sunlight, in electrical energy are very varied and there is often the possibility of the appearance of new applications. Much has been discussed about solar cell applications in clothing, backpacks, parking ceilings and in electronic packaging. These types of applications do not require high-performance devices, but they do require low-cost processing and, above all, that they are flexible. Flexible photovoltaic devices must then be manufactured by simple processing techniques to allow their eventual mass production. This work intends to contribute to the choice of materials to be used in flexible photovoltaic devices, focusing their development on organic bulk heterojunction solar cells (BHJ), which are commonly processed via solution. The structure chosen for the device was the multilayer one, where the transparent anode is the ITO (indium- tin oxide), followed by a hole transport layer (PEDOT:PSS), the active layer, and the cathode, which in our case was formed by calcium and aluminum, both deposited under vacuum. As active layer, the main element of study in this work, we studied the P3HT: PC61BM and the PTB7-Th: PC71BM, as electron donor (polymer) and electron acceptor elements (derived from fullerene). In particular with the device made with the PTB7-Th:PC71BM it was possible to changes processing parameters and thus enhancing its power conversion efficiency. Then, through current-voltage measurements (J-V), in the dark and under illumination, we were able to analyze the evolution of the cell parameters, such as the series (Rs) and shunt (Rp) resistances, as well as those that define the solar cell quality: short-circuit current (Jsc), open-circuit voltage (Voc), fill factor (FF), and efficiency (&#951;). Through the adjustments of the J-V curves, in the dark and under illumination, using J(V) expressions, for equivalent circuits of the diodes and solar cells respectively, we were able to perform a more effective analysis of how the series and shunt resistances change with the elements of the active layer and also with its processing. Fill factor (FF) is another important parameter that determines the energy conversion efficiency of an organic solar cell, and there are several factors that can significantly influence its value. This is one of the reasons why it is difficult to identify the true source of this parameter. This thesis also gave elements that correlate the chemical and morphological structure of the active layer with the fill factor.

Parmi les technologies photovoltaïques à base de silicium, les cellules solaires à hétérojonction a-Si:H/c-Si (HJ) ont montré une attention croissante en ce qui concerne leur fort potentiel d’amélioration du rendement et de la réduction de coûts. Dans cette thèse, des investigations sur les cellules solaires à hétérojonction a-Si:H/c-Si de type (n) développées à l'Institut National de l'Énergie Solaire sont présentées. Les aspects technologiques et physiques du dispositif à HJ ont été revus, en mettant l'accent sur la compréhension du rôle joué par la face arrière. À travers le développement et la mise en œuvre des films de a-Si:H intrinsèques et dopés (n) de haute qualité des cellules solaires à HJ, les conditions requises en face arrière des dispositifs ont été établies. Une comparaison entre plusieurs types de champ surface arrière, avec et sans l’introduction d’une couche buffer, est présentée et les caractéristiques des cellules solaires résultants sont discutées. Une discussion autour du contact arrière de cellules solaires à HJ est aussi présentée. Une nouvelle approche d’oxyde transparent conducteur en face arrière basé sur les couches d’oxyde de zinc dopé au bore (ZnO:B) est étudié. Dans le but de développer des couches de ZnO:B de haute qualité bien adaptées à leur utilisation dans des dispositifs à HJ, différents paramètres de dépôt ainsi que des traitements après dépôt comme le post plasma d’hydrogène ou le recuit laser sont étudiés et leur influence sur des cellules solaires est évaluée. Au cours de ce travail il est montré que la face arrière des cellules solaires à HJ joue un rôle important sur l’accomplissement de hauts rendements. Cependant, l'augmentation de la performance globale du dispositif dû à l’optimisation de la face arrière de la cellule est toujours dépendante des phénomènes ayant lieu en face avant des dispositifs. L'utilisation des films optimisés pour la face arrière des HJs développées dans cette thèse, associée à des couches améliorées pour la face avant et une nouvelle approche de métallisation nous a permis d’atteindre un rendement de conversion record de plus de 22%, démontrant ainsi le grand potentiel de cette technologie à HJ de a-Si:H/c-Si. / Amongst available silicon-based photovoltaic technologies, a-Si:H/c-Si heterojunctions (HJ) have raised growing attention because of their potential for further efficiency improvement and cost reduction. In this thesis, research on n-type a-Si:H/c-Si heterojunction solar cells developed at the Institute National de l’Énergie Solaire is presented. Technological and physical aspects of HJ devices are reviewed, with the focus on the comprehension of the back side role. Then, an extensive work to optimise amorphous layers used at the rear side of our devices as well as back contact films is addressed. Through the development and implementation of high-quality intrinsic and n-doped a-Si:H films on HJ solar cells, the needed requirements at the back side of devices are established. A comparison between different back surface fields (BSF) with and without the inclusion of a buffer layer is presented and resulting solar cell output characteristics are discussed. A discussion on the back contact of HJ solar cells is also presented. A new back TCO approach based on boron-doped zinc oxide (ZnO:B) layers is studied. With the aim of developing high-quality ZnO:B layers well-adapted to their use in HJ devices, different deposition parameters as well as post-deposition treatments such as post-hydrogen plasma or excimer laser annealing are studied, and their influence on solar cells is assessed. Throughout this work it is evidenced that the back side of HJ solar cells plays an important role on the achievement of high efficiencies. However, the enhancement of the overall device performance due to the back side optimisation is always dependent on phenomena taking place at the front side of devices. The use of the optimised back side layers developed in this thesis, together with improved front side layers and a novel metallisation approach have permitted a record conversion efficiency over 22%, thus demonstrating the great potential of this technology.

Le travail porte sur le développement et l’optimisation de transistors bipolaires à hétérojonction (TBH) SiGe et SiGeC par conception technologique assistée par ordinateur (TCAD). L'objectif est d'aboutir à un dispositif performant réalisable technologiquement, en tenant compte de tous les paramètres : étapes de fabrication technologiques, topologie du transistor, modèles physiques. Les études menées permettent d’atteindre les meilleures performances, en particulier une amélioration importante de la fréquence maximale d’oscillation (fMAX). Ce travail est la première approche développée pour la simulation des TBH SiGeC qui prend en compte l'impact de la contrainte et de la teneur en germanium et en carbone dans la base; conjointement pour les simulations des procédés de fabrication et les simulations électriques.Pour ce travail, nous avons développé et implémenté dans le simulateur TCAD des méthodes d'extraction de fMAX prenant en compte les éléments parasites intrinsèques et extrinsèques. Nous avons développé et implémenté un modèle pour la densité effective d’états fonction de la teneur en germanium et en carbone dans la base. Les modèles pour la bande interdite, la mobilité et le temps de relaxation de l'énergie sont calibrés sur la base de simulations Monte-Carlo.Les différentes analyses présentées dans cette thèse portent sur six variantes technologiques de TBH. Trois nouvelles architectures de TBH SiGeC avancés ont été élaborées et proposées pour des besoins basse et haute performance. Grace aux résultats obtenus, le meilleur compromis entre les différents paramètres technologiques et dimensionnels permettent de fabriquer un TBH SiGeC avec une valeur de fMAX de 500 GHz, réalisant ainsi l’objectif principal de la thèse. / The present work investigates the technology development of state-of-the-art SiGe and SiGeC Heterojunction Bipolar Transistors (HBT) by means of technology computer aided design (TCAD). The objective of this work is to obtain an advanced HBT very close to the real device not only in its process fabrication steps, but also in its physical behavior, geometric architecture, and electrical results. This investigation may lead to achieve the best electrical performances for the devices studied, in particular a maximum operating frequency of 500 GHz. The results of this work should help to obtain more physical and realistic simulations, a better understanding of charge transport, and to facilitate the development and optimization of SiGe and SiGeC HBT devices.The TCAD simulation kits for SiGe/SiGeC HBTs developed during our work have been carried out in the framework of the STMicroelectronics bipolar technology evolution. In order to achieve accurate simulations we have used, developed, calibrated and implemented adequate process models, physical models and extraction methodologies. To our knowledge, this work is the first approach developed for SiGe/SiGeC HBTs which takes into account the impact of the strain, and of the germanium and carbon content in the base, for both: process and electrical simulations.In this work we will work with the successive evolutions of B3T, B4T and B5T technologies. For each new device fMAX improves of 100 GHz, thus the technology B3T matches to 300 GHz, B4T and B5T to 400 and 500 GHz, respectively.Chapter one introduces the SiGe SiGeC heterojunction bipolar technologies and their operating principles. This chapter deals also with the high frequency AC transistor operation, the extraction methods for fMAX and the carrier transport in extremely scaled HBTs.Chapter two analyzes the physical models adapted to SiGeC strained alloys used in this work and the electrical simulation of HBT devices. This is also an important work of synthesis leading to the selection, implementation and development of dedicated models for SiGeC HBT simulation.Chapter three describes the B3T TCAD simulation platform developed to obtain an advanced HBT very close to the real device. In this chapter the process fabrication of the B3T technology is described together with the methodology developed to simulate advanced HBT SiGeC devices by means of realistic TCAD simulations.Chapter four describes the HBT architectures developed during this work. We will propose low-cost structures with less demanding performance requirements and highly performing structures but with a higher cost of production. The B4T architecture which has been manufactured in clean-room is deeply studied in this chapter. The impact of the main fabrication steps is analyzed in order to find the keys process parameters to increase fMAX without degrading other important electrical characteristics. At the end of this chapter the results obtained is used to elaborate a TCAD simulation platform taking into account the best trade-off of the different key process parameters to obtain a SiGeC HBT working at 500 GHz of fMAX.

In this dissertation, we investigate two emerging strategies for enhancing the performance of organic photovoltaics. The first takes advantage of a process called singlet exciton fission, and the second embodies an exodus from the fullerene electron acceptors prominent in organic solar cells. Indeed, this versatile class of tunable small molecules are aptly termed nonfullerene acceptors. However, both strategies would benefit from a greater understanding of underlying principles. Singlet exciton fission is a photon-multiplying process in which a singlet exciton from a high-energy absorbed photon splits into two triplet excitons. The process could significantly reduce energy lost to heat in photovoltaic devices, but its mechanisms are still misunderstood. One model involves direct coupling between the singlet and triplet states, and another model involves an intermediate charge transfer state. Transient absorption spectroscopy allowed us to examine singlet fission in films of pentacene, fluorinated pentacene, and coevaporated blends of various mixing ratios. We directly observe an intermolecular charge transfer state during singlet fission in solid films of coevaporated pentacene and peruoropentacene, which supports the model of charge transfer state-mediated singlet fission. Furthermore, we successfully induced singlet fission in one blend by directly exciting the charge transfer state below the bandgap. We use various types of steady state and time-resolved spectroscopy to characterize two types of nonfullerene electron acceptors. The first type is a group of tetraazabenzodiuoranthene diimide (BFI) dimers and a BFI monomer. The BFI dimers were designed to have twisted, nonplanar 3-dimensional structures and have helped achieve power conversion efficiencies of over 8% in organic solar cells. The other type of nonfullerene acceptor is a calamitic small molecule, and we consider the BAF-4CN electron acceptor, which has also been used in a solar cell whose efficiency exceeded 8%. Spectroscopic studies give insight into the performances of these nonfullerene devices in relation to fullerene-derivative counterparts. We find that the nonfullerene blends suffer from more geminate charge recombination. However, despite this drawback, in some cases, slower rates of nongeminate recombination may lead to successful power conversion efficiencies in nonfullerene solar cells.