Academic literature on the topic 'Pool hopping'

Pool hopping attack is the result of miners leaving the pool when it offers fewer financial rewards and joining back when the rewards of mining yield higher rewards in blockchain networks. This act of leaving and rejoining the pool only during the good times results in the miner receiving more rewards than the computational power they contribute. Miners exiting the pool deprive it of its collective hash power, which leaves the pool unable to mine the block successfully. This results in its competitors mining the block before they can finish mining. Existing research shows pool hopping resistant measures and detection strategies; however, they do not offer any robust preventive solution to discourage miners from leaving the mining pool. To prevent pool hopping attacks, a smart contract-based pool hopping attack prevention model is proposed. The main objective of our research is maintaining the symmetrical relationship between the miners by requiring them all to continually contribute their computational power to successfully mine a block. We implement a ledger containing records of all miners, in the form of a miner certificate, which tracks the history of the miner’s earlier behavior. The certificate enables a pool manager to better initiate terms of the smart contract, which safeguards the interests of existing mining pool members. The model prevents frequent mine hoppers from pool hopping as they submit coins in the form of an escrow and risk losing them if they abandon the pool before completing mining of the block. The key critical factors that every pool hopping attack prevention solution must address and a study of comparative analysis with existing solutions are presented in the paper.

This paper presents numerical simulation and compact modeling of 2,7-Dioctyl {1} benzothieno {3,2-b}{1} benzothiophene (C8-BTBT-C8) organic semiconductor-based TFT. It shows the entire modeling process flow of this organic semiconductor (OSC) and tests the device realization using a ring oscillator. The paper comprises OSC characterisation, band-gap modeling, electrostatic modeling, and capacitance modeling. The TCAD model consists of the Hopping and Pool Frenkel premise and characterizes the Density of State (DOS) for traps in deep and tail states. The findings from this research provide valuable information for improving OTFT models, enhancing their predictive accuracy, and advancing the understanding of organic semiconductor device behavior. The electrostatics demonstrate device structure dependency

In this study we report interface and carrier transport behaviour in Al/HfO2/SiO2/SiC MIS structure. The density of the interface states (Dit) and the oxide trapped charges (Not) are found to be ~7 x 1011 eV-1cm-2 @ Ec-Et = 0.2 eV, and ~ 4.8 x 1011 cm-2. The temperature dependencies on gate current density are explored to study the different charge transport mechanisms through the HfO2-based dielectric stack on 4H-SiC. In the low voltage region, the conduction mechanism is controlled by a space charge limited or electronic hopping conduction process. Beyond this region (1.25 MV/cm <E <2.45MV/cm), leakage current consists of combination of Pool-Frenkel (PF) and Schottky emission The trap energy level is found to be ~0.6 eV. In the higher field region (> 2.5 MV/cm), and at higher temperatures Schottky emission (SE) fits the data very well. The barrier height is found to be ~1.5 eV, which is higher than the value for just HfO2 on SiC

The constant innovation of devices in the semiconductor industry to improve performance to meet very specific demands has led to the study and exploration of a host of new materials. The use of ternary and quaternary materials, organic materials, amorphous silicon are a few examples of promising alternatives to traditional crystalline silicon. However, the use of novel materials presents a unique challenge for a theoretical analysis using device simulation. Traditional device simulation methods are sometimes not enough to capture the nuances of transport. In this paper we study transport through amorphous silicon to evaluate it's role in a-Si/c-Si HIT Cell and it's potential for other device operations by the use of Kinetic Monte Carlo (KMC) method. As an amorphous materials lack long range order, it is near impossible to create a bandstructure for it and conduct Ensemble Monte Carlo (EMC) simulations to study transport through the material. Also, the presence of many defects creates localized states below the conduction band which facilitates hopping transport. As hopping transport happens through a series of capture and emission processes, the time scales of these mechanisms render the use of a traditional EMC unfeasible. It is crucial to understand the nature of the defects/traps that are present in the amorphous material. Understanding defect assisted transport is the key to understanding how the amorphous silicon layer will affect overall device performance. Defect assisted transport (DAT) can be conducted in the amorphous material through various different mechanisms such as capture of carriers by a defect, tunneling emission, Pool-Frenkel emission, defect to defect transition etc. Using the Kinetic Monte Carlo approach we will be able to simulate individual charge carriers that interact with point like defects over a period of time. However, the transient nature of the KMC is not limited to short time scales. Also, the suggested method can be used to study the effect of many transition mechanisms. This method facilitates the simulation of the many individual steps in a Markovian chain that mimics carriers moving through various defects. We study hopping transport through a triangular barrier with use of phonon assisted mechanisms to analyze current and carrier transit times. The distribution function is also analyzed before and after defect assisted transport. One of our primary objectives is to study the role played by the amorphous silicon layer in determining overall device performance of a-Si/c-Si HIT Cell.

In recent years, districts have paid special attention to the common practice of “district hopping,” families bending geographic school assignment rules by sending a child to a school in a district where the child does not formally reside—usually to a district that is more desirable because of higher performing schools or greater educational resources. In several high-profile cases, mothers who engaged in district hopping were charged with “grand theft” of educational services. By situating these cases in the broader context of market-based reforms, we refocus attention on the responses of districts rather than the actions of parents. We argue that increased privatization of education and growing dominance of a “private-goods” model of schooling create the conditions necessary for framing these actions as “theft.”

The field dependences of the electrical conductivity of Pt/diamond-like carbon (DLC)/Pt structures based on thin layers of high-resistivity DLC are studied. It is shown that the nonohmic behavior of theconductance of structures is described by the Frenkel–Poole formula and is related to correlated distribution of charges under conditions of their percolation hopping transport between low-resistance DLC regions.

Thin films of In2Se3 were prepared by thermal evaporation. X-ray diffraction indicated that the as-grown films were amorphous in nature and became polycrystalline γ-In2Se3 films after annealing. The ac conductivity and dielectric properties of In2Se3 films have been investigated in the frequency range 100 Hz–100 kHz. The ac conductivity σ ac is found to be proportional to ωn where n < 1. The temperature dependence of both ac conductivity and the parameter n is reasonably well interpreted by the correlated barrier hopping (CBH) model. The values of dielectric constant ε and loss tangent tan δ were found to increase with frequency and temperature. The ac conductivity of the films was found to be hopping mechanism. In I–V characteristic for different field and temperature were studied and it has been found that the conduction process is Poole–Frenkel type.

A study of the electrical conduction mechanism in polyimide (Kapton) films has been made. The measurements were carried out on films of 12.5 and 25 µm thick in the voltage range of 100 to 3000 V and in the temperature range of 300 to 373 K. The conduction mechanism in the low field region is a hopping type process while the high field phenomenon is a Poole-Frenkel behavior. The activation energy is about 1.1 eV at 100 V and 0.8 eV at 3000 V.

Bitcoin est une crypto-monnaie pionnière qui enregistre les transactions dans un registre public et distribué appelé blockchain. Il est utilisé comme support pour les paiements, les investissements et plus largement la gestion d’un portefeuille numérique qui n’est pas administré par un gouvernement ou une institution financière. Au cours de ces dix dernières années, l’activité transactionnelle de Bitcoin a rapidement et largement augmenté. La volumétrie ainsi que la nature évolutive de ces données posent des défis pour l’analyse et l'exploration des usages ainsi que des activités sur la blockchain. Le domaine de l’analyse visuelle travaille sur la conception de systèmes analytiques qui permettent aux humains d'interagir et d'obtenir des informations à partir de données complexes. Dans cette thèse, j'apporte plusieurs contributions à l'analyse des activités de minage sur la blockchain Bitcoin. Tout d'abord, je propose une caractérisation des travaux passés et des défis de recherche liés à l’analyse visuelle pour les blockchains. À partir de cette étude, j'ai proposé un outil d’analyse visuelle pour comprendre les activités de minage qui sont essentielles pour maintenir l'intégrité et la sécurité des données sur la blockchain Bitcoin. Je propose une méthode pour extraire l’activité des mineurs à partir des données de transaction et tracer leur comportement de bascule d’un pool de minage à un autre. L'analyse empirique de ces données a notamment révélé que les nouveaux pools de minage offraient une meilleure incitation et attiraient davantage de mineurs. Cette analyse a également montré que les mineurs choisissaient stratégiquement leur pool de minage dans le but de maximiser leur profit. Pour explorer l'évolution et la dynamique de cette activité sur le long terme, j'ai développé un outil d’analyse visuelle, appelé MiningVis, qui intègre des données liées au comportement des mineurs avec des informations contextuelles issues des statistiques et de l’actualité de Bitcoin. L'étude avec des utilisateurs démontre que les participants au minage de Bitcoin cherchent à utiliser l'outil pour analyser l'activité globale plutôt que pour étudier les détails d’un pool de minage. Les commentaires des participants prouvent que l'outil les a aidés à mettre en relation plusieurs informations et à découvrir les tendances dans l’activité de minage de Bitcoin
Bitcoin is a pioneer cryptocurrency that records transactions in a public distributed ledger called the blockchain. It has been used as a medium for payments, investments, and digital wallets that are not controlled by any government or financial institution. Over the past ten years, transaction activities in Bitcoin have increased rapidly. The volume and evolving nature of its data pose analysis challenges to explore diverse groups of users and different activities on the network. The field of Visual Analytics (VA) has been working on the development of analytical systems that allow humans to interact and gain insights from complex data. In this thesis, I make several contributions to the analysis of Bitcoin mining activity. First, I provide a characterization of the past work and research challenges related to VA for blockchains. From this assessment, I proposed a VA tool to understand mining activities that ensure data integrity and security on the Bitcoin blockchain. I propose a method to extract miners from the transaction data and trace pool hopping behavior. The empirical analysis of this data revealed that emerging mining pools provided a better incentive to attract miners. Simultaneously, miners strategically chose mining pools to maximize their profit. To explore the evolution and dynamics of this activity over the long term, I developed a VA tool called MiningVis that integrates mining behavior data with contextual information from Bitcoin statistics and news. The user study demonstrates that Bitcoin miner participants use the tool to analyze higher-level mining activity rather than mining pool details. The evaluation of the tool proves that it helped participants to relate multiple information and discover historical trends of Bitcoin mining

Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devices
Organische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile

Die Bestrahlung von tetraedrisch amorphen Kohlenstoff (ta-C) mit schnellen schweren Ionen führt zur Bildung von mikroskopischen elektrisch leitfähigen Ionenspuren mit Durchmessern um 10 nm. Dieses Phänomen ist auf das sp² zu sp³ Hybridisierungsverhältnis des amorphen Kohlenstoffes zurückzuführen. Das einschlagende Ion deponiert eine große Menge Energie innerhalb des Spurvolumens, so dass eine Materialtransformation hin zu höheren sp² Hybridisierung stattfindet. Hierdurch wird die elektrische Leitfähigkeit der Ionenspur stark erhöht. Dieser Effekt kann durch die Zugabe von Verunreinigungen wie Kupfer verstärkt werden. Das Ziel dieser Arbeit ist die umfassende Analyse des elektrischen Verhaltens von ta-C mit besonderen Augenmerk auf die Auswirkungen von Kupferverunreinigungen und Ionenspuren. Der Effekt von Kupferverunreinigungen auf das wichtige Hybridisierungsverhältnis vom amorphen Kohlenstoff wird vermessen. Darüber hinaus wurden alle Proben elektrisch mit makroskopischen Kontakten im Temperaturbeireich von 20 K bis 380 K analysiert. Mikroskopisch wurden einzelne leitfähige Ionenspuren mit Hilfe von atomarer Kraftmikroskopie betrachtet. Die statistische Verteilung der Spureigenschaften in Kohlenstofffilmen mit verschiedenen Kupferkonzentrationen werden verglichen, um die Spurbildung besser zu verstehen. Die normalisierten durchschnittlichen Spurleitfähigkeiten aus mikroskopischen und makroskopischen Messungen werden verglichen. Hierbei kann die Zuverlässigkeit der beiden experimentellen Methoden bewertet werden und mögliche Fehlerquellen ausfindig gemacht werden. Schließlich wird ein Konzept für eine Anwendung unterbrochener Ionenspuren gezeigt.

Organic semiconductors are a new key technology for large-area and flexible thin-film electronics. They are deposited as thin films (sub-nanometer to micrometer) on large-area substrates. The technologically most advanced applications are organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). For the improvement of performance and efficiency, correct modeling of the electronic processes in the devices is essential. Reliable characterization and validation of the electronic properties of the materials is simultaneously required for the successful optimization of devices. Furthermore, understanding the relations between material structures and their key characteristics opens the path for innovative material and device design. In this thesis, two material characterization methods are developed, respectively refined and applied: a novel technique for measuring the charge carrier mobility μ and a way to determine the ionization energy IE or the electron affinity EA of an organic semiconductor. For the mobility measurements, a new evaluation approach for space-charge limited current (SCLC) measurements in single carrier devices is developed. It is based on a layer thickness variation of the material under investigation. In the \"potential mapping\" (POEM) approach, the voltage as a function of the device thickness V(d) at a given current density is shown to coincide with the spatial distribution of the electric potential V(x) in the thickest device. On this basis, the mobility is directly obtained as function of the electric field F and the charge carrier density n. The evaluation is model-free, i.e. a model for μ(F, n) to fit the measurement data is not required, and the measurement is independent of a possible injection barrier or potential drop at non-optimal contacts. The obtained μ(F, n) function describes the effective average mobility of free and trapped charge carriers. This approach realistically describes charge transport in energetically disordered materials, where a clear differentiation between trapped and free charges is impossible or arbitrary. The measurement of IE and EA is performed by characterizing solar cells at varying temperature T. In suitably designed devices based on a bulk heterojunction (BHJ), the open-circuit voltage Voc is a linear function of T with negative slope in the whole measured range down to 180K. The extrapolation to temperature zero V0 = Voc(T → 0K) is confirmed to equal the effective gap Egeff, i.e. the difference between the EA of the acceptor and the IE of the donor. The successive variation of different components of the devices and testing their influence on V0 verifies the relation V0 = Egeff. On this basis, the IE or EA of a material can be determined in a BHJ with a material where the complementary value is known. The measurement is applied to a number of material combinations, confirming, refining, and complementing previously reported values from ultraviolet photo electron spectroscopy (UPS) and inverse photo electron spectroscopy (IPES). These measurements are applied to small molecule organic semiconductors, including mixed layers. In blends of zinc-phthalocyanine (ZnPc) and C60, the hole mobility is found to be thermally and field activated, as well as increasing with charge density. Varying the mixing ratio, the hole mobility is found to increase with increasing ZnPc content, while the effective gap stays unchanged. A number of further materials and material blends are characterized with respect to hole and electron mobility and the effective gap, including highly diluted donor blends, which have been little investigated before. In all materials, a pronounced field activation of the mobility is observed. The results enable an improved detailed description of the working principle of organic solar cells and support the future design of highly efficient and optimized devices.:1. Introduction 2. Organic semiconductors and devices 2.1. Organic semiconductors 2.1.1. Conjugated π system 2.1.2. Small molecules and polymers 2.1.3. Disorder in amorphous materials 2.1.4. Polarons 2.1.5. Polaron hopping 2.1.6. Fermi-Dirac distribution and Fermi level 2.1.7. Quasi-Fermi levels 2.1.8. Trap states 2.1.9. Doping 2.1.10. Excitons 2.2. Interfaces and blend layers 2.2.1. Interface dipoles 2.2.2. Energy level bending 2.2.3. Injection from metal into semiconductor, and extraction 2.2.4. Excitons at interfaces 2.3. Charge transport and recombination in organic semiconductors 2.3.1. Drift transport 2.3.2. Charge carrier mobility 2.3.3. Thermally activated transport 2.3.4. Diffusion transport 2.3.5. Drift-diffusion transport 2.3.6. Space-charge limited current 2.3.7. Recombination 2.4. Mobility measurement 2.4.1. SCLC and TCLC 2.4.2. Time of flight 2.4.3. Organic field effect transistors 2.4.4. CELIV 2.5. Organic solar cells 2.5.1. Exciton diffusion towards the interface 2.5.2. Dissociation of CT states 2.5.3. CT recombination 2.5.4. Flat and bulk heterojunction 2.5.5. Transport layers 2.5.6. Thin film optics 2.5.7. Current-voltage characteristics and equivalent circuit 2.5.8. Solar cell efficiency 2.5.9. Limits of efficiency 2.5.10. Correct solar cell characterization 2.5.11. The \"O-Factor\" 3. Materials and experimental methods 3.1. Materials 3.2. Device fabrication and layout 3.2.1. Layer deposition 3.2.2. Encapsulation 3.2.3. Homogeneity of layer thickness on a wafer 3.2.4. Device layout 3.3. Characterization 3.3.1. Electrical characterization 3.3.2. Sample illumination 3.3.3. Temperature dependent characterization 3.3.4. UPS 4. Simulations 5.1. Design of single carrier devices 5.1.1. General design requirements 5.1.2. Single carrier devices for space-charge limited current 5.1.3. Ohmic regime 5.1.4. Design of injection and extraction layers 5.2. Advanced evaluation of SCLC – potential mapping 5.2.1. Potential mapping by thickness variation 5.2.2. Further evaluation of the transport profile 5.2.3. Injection into and extraction from single carrier devices 5.2.4. Majority carrier approximation 5.3. Proof of principle: POEM on simulated data 5.3.1. Constant mobility 5.3.2. Field dependent mobility 5.3.3. Field and charge density activated mobility 5.3.4. Conclusion 5.4. Application: Transport characterization in organic semiconductors 5.4.1. Hole transport in ZnPc:C60 5.4.2. Hole transport in ZnPc:C60 – temperature variation 5.4.3. Hole transport in ZnPc:C60 – blend ratio variation 5.4.4. Hole transport in ZnPc:C70 5.4.5. Hole transport in neat ZnPc 5.4.6. Hole transport in F4-ZnPc:C60 5.4.7. Hole transport in DCV-5T-Me33:C60 5.4.8. Electron transport in ZnPc:C60 5.4.9. Electron transport in neat Bis-HFl-NTCDI 5.5. Summary and discussion of the results 5.5.1. Phthalocyanine:C60 blends 5.5.2. DCV-5T-Me33:C60 5.5.3. Conclusion 6. Organic solar cell characteristics: the influence of temperature 6.1. ZnPc:C60 solar cells 6.1.1. Temperature variation 6.1.2. Illumination intensity variation 6.2. Voc in flat and bulk heterojunction organic solar cells 6.2.1. Qualitative difference in Voc(I, T) 6.2.2. Interpretation of Voc(I, T) 6.3. BHJ stoichiometry variation 6.3.1. Voc upon variation of stoichiometry and contact layer 6.3.2. V0 upon stoichiometry variation 6.3.3. Low donor content stoichiometry 6.3.4. Conclusion from stoichiometry variation 6.4. Transport material variation 6.4.1. HTM variation 6.4.2. ETM variation 6.5. Donor:acceptor material variation 6.5.1. Donor variation 6.5.2. Acceptor variation 6.6. Conclusion 7. Summary and outlook 7.1. Summary 7.2. Outlook A. Appendix A.1. Energy pay-back of this thesis A.2. Tables and registers
Organische Halbleiter sind eine neue Schlüsseltechnologie für großflächige und flexible Dünnschichtelektronik. Sie werden als dünne Materialschichten (Sub-Nanometer bis Mikrometer) auf großflächige Substrate aufgebracht. Die technologisch am weitesten fortgeschrittenen Anwendungen sind organische Leuchtdioden (OLEDs) und organische Photovoltaik (OPV). Zur weiteren Steigerung von Leistungsfähigkeit und Effizienz ist die genaue Modellierung elektronischer Prozesse in den Bauteilen von grundlegender Bedeutung. Für die erfolgreiche Optimierung von Bauteilen ist eine zuverlässige Charakterisierung und Validierung der elektronischen Materialeigenschaften gleichermaßen erforderlich. Außerdem eröffnet das Verständnis der Zusammenhänge zwischen Materialstruktur und -eigenschaften einen Weg für innovative Material- und Bauteilentwicklung. Im Rahmen dieser Dissertation werden zwei Methoden für die Materialcharakterisierung entwickelt, verfeinert und angewandt: eine neuartige Methode zur Messung der Ladungsträgerbeweglichkeit μ und eine Möglichkeit zur Bestimmung der Ionisierungsenergie IE oder der Elektronenaffinität EA eines organischen Halbleiters. Für die Beweglichkeitsmessungen wird eine neue Auswertungsmethode für raumladungsbegrenzte Ströme (SCLC) in unipolaren Bauteilen entwickelt. Sie basiert auf einer Schichtdickenvariation des zu charakterisierenden Materials. In einem Ansatz zur räumlichen Abbildung des elektrischen Potentials (\"potential mapping\", POEM) wird gezeigt, dass das elektrische Potential als Funktion der Schichtdicke V(d) bei einer gegebenen Stromdichte dem räumlichen Verlauf des elektrischen Potentials V(x) im dicksten Bauteil entspricht. Daraus kann die Beweglichkeit als Funktion des elektrischen Felds F und der Ladungsträgerdichte n berechnet werden. Die Auswertung ist modellfrei, d.h. ein Modell zum Angleichen der Messdaten ist für die Berechnung von μ(F, n) nicht erforderlich. Die Messung ist außerdem unabhängig von einer möglichen Injektionsbarriere oder einer Potentialstufe an nicht-idealen Kontakten. Die gemessene Funktion μ(F, n) beschreibt die effektive durchschnittliche Beweglichkeit aller freien und in Fallenzuständen gefangenen Ladungsträger. Dieser Zugang beschreibt den Ladungstransport in energetisch ungeordneten Materialien realistisch, wo eine klare Unterscheidung zwischen freien und Fallenzuständen nicht möglich oder willkürlich ist. Die Messung von IE und EA wird mithilfe temperaturabhängiger Messungen an Solarzellen durchgeführt. In geeigneten Bauteilen mit einem Mischschicht-Heteroübergang (\"bulk heterojunction\" BHJ) ist die Leerlaufspannung Voc im gesamten Messbereich oberhalb 180K eine linear fallende Funktion der Temperatur T. Es kann bestätigt werden, dass die Extrapolation zum Temperaturnullpunkt V0 = Voc(T → 0K) mit der effektiven Energielücke Egeff , d.h. der Differenz zwischen EA des Akzeptor-Materials und IE des Donator-Materials, übereinstimmt. Die systematische schrittweise Variation einzelner Bestandteile der Solarzellen und die Überprüfung des Einflusses auf V0 bestätigen die Beziehung V0 = Egeff. Damit kann die IE oder EA eines Materials bestimmt werden, indem man es in einem BHJ mit einem Material kombiniert, dessen komplementärer Wert bekannt ist. Messungen per Ultraviolett-Photoelektronenspektroskopie (UPS) und inverser Photoelektronenspektroskopie (IPES) werden damit bestätigt, präzisiert und ergänzt. Die beiden entwickelten Messmethoden werden auf organische Halbleiter aus kleinen Molekülen einschließlich Mischschichten angewandt. In Mischschichten aus Zink-Phthalocyanin (ZnPc) und C60 wird eine Löcherbeweglichkeit gemessen, die sowohl thermisch als auch feld- und ladungsträgerdichteaktiviert ist. Wenn das Mischverhältnis variiert wird, steigt die Löcherbeweglichkeit mit zunehmendem ZnPc-Anteil, während die effektive Energielücke unverändert bleibt. Verschiedene weitere Materialien und Materialmischungen werden hinsichtlich Löcher- und Elektronenbeweglichkeit sowie ihrer Energielücke charakterisiert, einschließlich bisher wenig untersuchter hochverdünnter Donator-Systeme. In allen Materialien wird eine deutliche Feldaktivierung der Beweglichkeit beobachtet. Die Ergebnisse ermöglichen eine verbesserte Beschreibung der detaillierten Funktionsweise organischer Solarzellen und unterstützen die künftige Entwicklung hocheffizienter und optimierter Bauteile.:1. Introduction 2. Organic semiconductors and devices 2.1. Organic semiconductors 2.1.1. Conjugated π system 2.1.2. Small molecules and polymers 2.1.3. Disorder in amorphous materials 2.1.4. Polarons 2.1.5. Polaron hopping 2.1.6. Fermi-Dirac distribution and Fermi level 2.1.7. Quasi-Fermi levels 2.1.8. Trap states 2.1.9. Doping 2.1.10. Excitons 2.2. Interfaces and blend layers 2.2.1. Interface dipoles 2.2.2. Energy level bending 2.2.3. Injection from metal into semiconductor, and extraction 2.2.4. Excitons at interfaces 2.3. Charge transport and recombination in organic semiconductors 2.3.1. Drift transport 2.3.2. Charge carrier mobility 2.3.3. Thermally activated transport 2.3.4. Diffusion transport 2.3.5. Drift-diffusion transport 2.3.6. Space-charge limited current 2.3.7. Recombination 2.4. Mobility measurement 2.4.1. SCLC and TCLC 2.4.2. Time of flight 2.4.3. Organic field effect transistors 2.4.4. CELIV 2.5. Organic solar cells 2.5.1. Exciton diffusion towards the interface 2.5.2. Dissociation of CT states 2.5.3. CT recombination 2.5.4. Flat and bulk heterojunction 2.5.5. Transport layers 2.5.6. Thin film optics 2.5.7. Current-voltage characteristics and equivalent circuit 2.5.8. Solar cell efficiency 2.5.9. Limits of efficiency 2.5.10. Correct solar cell characterization 2.5.11. The \"O-Factor\" 3. Materials and experimental methods 3.1. Materials 3.2. Device fabrication and layout 3.2.1. Layer deposition 3.2.2. Encapsulation 3.2.3. Homogeneity of layer thickness on a wafer 3.2.4. Device layout 3.3. Characterization 3.3.1. Electrical characterization 3.3.2. Sample illumination 3.3.3. Temperature dependent characterization 3.3.4. UPS 4. Simulations 5.1. Design of single carrier devices 5.1.1. General design requirements 5.1.2. Single carrier devices for space-charge limited current 5.1.3. Ohmic regime 5.1.4. Design of injection and extraction layers 5.2. Advanced evaluation of SCLC – potential mapping 5.2.1. Potential mapping by thickness variation 5.2.2. Further evaluation of the transport profile 5.2.3. Injection into and extraction from single carrier devices 5.2.4. Majority carrier approximation 5.3. Proof of principle: POEM on simulated data 5.3.1. Constant mobility 5.3.2. Field dependent mobility 5.3.3. Field and charge density activated mobility 5.3.4. Conclusion 5.4. Application: Transport characterization in organic semiconductors 5.4.1. Hole transport in ZnPc:C60 5.4.2. Hole transport in ZnPc:C60 – temperature variation 5.4.3. Hole transport in ZnPc:C60 – blend ratio variation 5.4.4. Hole transport in ZnPc:C70 5.4.5. Hole transport in neat ZnPc 5.4.6. Hole transport in F4-ZnPc:C60 5.4.7. Hole transport in DCV-5T-Me33:C60 5.4.8. Electron transport in ZnPc:C60 5.4.9. Electron transport in neat Bis-HFl-NTCDI 5.5. Summary and discussion of the results 5.5.1. Phthalocyanine:C60 blends 5.5.2. DCV-5T-Me33:C60 5.5.3. Conclusion 6. Organic solar cell characteristics: the influence of temperature 6.1. ZnPc:C60 solar cells 6.1.1. Temperature variation 6.1.2. Illumination intensity variation 6.2. Voc in flat and bulk heterojunction organic solar cells 6.2.1. Qualitative difference in Voc(I, T) 6.2.2. Interpretation of Voc(I, T) 6.3. BHJ stoichiometry variation 6.3.1. Voc upon variation of stoichiometry and contact layer 6.3.2. V0 upon stoichiometry variation 6.3.3. Low donor content stoichiometry 6.3.4. Conclusion from stoichiometry variation 6.4. Transport material variation 6.4.1. HTM variation 6.4.2. ETM variation 6.5. Donor:acceptor material variation 6.5.1. Donor variation 6.5.2. Acceptor variation 6.6. Conclusion 7. Summary and outlook 7.1. Summary 7.2. Outlook A. Appendix A.1. Energy pay-back of this thesis A.2. Tables and registers

In 5G NR systems, users with restricted signal bandwidth may suffer from poor positioning and range performance. In this paper, we present a detailed performance analysis of the frequency hopping method, allowing such users to cover significantly more frequency bandwidth while having a relatively small signal bandwidth in a given time interval. The performance is investigated in a non-stationary frequency selective channel in the absence of phase continuity between hops using coherent or non-coherent joint full frequency bandwidth signal processing algorithms. It was shown that the correct operation of the coherent algorithm requires the phase errors compensation between each pair of signal frequency hops. The proposed non-coherent signal processing algorithm does not require correction of the signal phases and demonstrates its advantages for high mobility users in comparison with the coherent algorithm.

Rachel is eight years old. She was slow to crawl and walk. She still cannot pedal a tricycle, fasten small buttons, or tie her laces. She is very poor at sports and is often teased by the other children for her awkward running style. She is a messy eater and washes herself and brushes her teeth with great difficulty. Her mother says that she has a poor sense of direction and still confuses right with left. Rachel’s school work is satisfactory. Her writing is untidy, but if she prints slowly it is legible. Rachel has been tested by a psychologist and found to have some visual perception difficulties, but to be of normal intelligence. Her reading, spelling, and arithmetic are in the average range. A paediatrician has examined Rachel and detected no abnormalities that can account for her clumsiness. The term ‘clumsiness’ will be used in this chapter to refer to unexplained, significant difficulties in the coordination of movement in a child of average, or above average, intelligence. This sort of clumsiness is commonly associated with other forms of specific learning difficulty, such as reading difficulty. This does not mean, however, that most children with specific learning difficulty are clumsy. Many are, in fact, well coordinated. But clumsiness is far more common in children with specific learning difficulty than in other children. Clumsiness is more common in boys and quite often runs in families. The word ‘motor’ is used for movement. Gross motor skills involve large groups of muscles responsible for activities such as walking, running, jumping, hopping, and bicycle riding. Fine motor skills involve the hands and fingers, and are concerned with activities such as writing, drawing, using scissors, and tying knots. There are a number of standardized tests of both gross and fine motor proficiency. These may be performed by a physiotherapist, an occupational therapist, or a doctor. Activities must be carefully observed to detect the presence of tremors and other unusual movements. Balance, strength, tone, reflexes, and ability to interpret certain sensations are all assessed. It is essential that rare, serious conditions associated with poor coordination are excluded by a doctor.