Microscopic Studies of the Fate of Charges in Organic Semiconductors
Microscopic Studies of the Fate of Charges in Organic Semiconductors

Author: Louisa Marion Smieska

Publisher:

Published: 2015

Total Pages: 230

ISBN-13:

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Organic semiconductors could have wide-ranging applications in lightweight, efficient electronic circuits. However, several fundamental questions regarding organic electronic device behavior have not yet been fully addressed, including the nature of chemical charge traps, and robust models for injection and transport. Many studies focus on engineering devices through bulk transport measurements, but it is not always possible to infer the microscopic behavior leading to the observed measurements. In this thesis, we present scanning-probe microscope studies of organic semiconductor devices in an effort to connect local properties with local device behavior. First, we study the chemistry of charge trapping in pentacene transistors. Working devices are doped with known pentacene impurities and the extent of charge trap formation is mapped across the transistor channel. Trap-clearing spectroscopy is employed to measure an excitation of the pentacene charge trap species, enabling identification of the degradationrelated chemical trap in pentacene. Second, we examine transport and trapping in peryelene diimide (PDI) transistors. Local mobilities are extracted from surface potential profiles across a transistor channel, and charge injection kinetics are found to be highly sensitive to electrode cleanliness. Trap-clearing spectra generally resemble PDI absorption spectra, but one derivative yields evidence indicating variation in trap-clearing mechanisms for different surface chemistries. Trap formation rates are measured and found to be independent of surface chemistry, contradicting a proposed silanol trapping mechanism. Finally, we develop a variation of scanning Kelvin probe microscopy that enables measurement of electric fields through a position modulation. This method avoids taking a numeric derivative of potential, which can introduce high-frequency noise into the electric field signal. Preliminary data is presented, and the theoretical basis for electric field noise in both methods is examined.

Energy and Charge Transfer in Organic Semiconductors
Energy and Charge Transfer in Organic Semiconductors

Author: Kohzoh Masuda

Publisher: Springer Science & Business Media

Published: 2012-12-06

Total Pages: 187

ISBN-13: 1468421093

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Great progress has been made in the field of ordinary semiconductor physics and associated technologies. For the time being, if we could use new materials such as organic semiconductors progress in electronics could be accelerated. Characteristics of organic semiconductors that are superior to others are: i) high photo-conductivity under irradiation along with low leakage current in the dark, ii) high sensitivity of the conductivity to various gases and to pressure. iii) possibility of using them in the amorphous state, iv) possibility of making devices of extremely small size, v) large variety of the materials, which makes suitable choice of material component easy. A possible future development is a highly conductive material which could be used for electric power transmission - and which might help solve some of the problems posed by transmission losses. The U.S.-Japan Seminar on Energy and Charge Transfer in Organic Semiconductors was held in Osaka Japan, 6-9 August, 1973. Completed results were summarized and the direction for the future was discussed. Information was exchanged quite freely and actively in a pleasant atmosphere. Many of the papers presented at the seminar are published here but unfortunately a few could not be included. It would give us great pleasure if this seminar could be one step in the further development of the research in this field.

Charge Dynamics in Organic Semiconductors
Charge Dynamics in Organic Semiconductors

Author: Pascal Kordt

Publisher: Walter de Gruyter GmbH & Co KG

Published: 2016-09-12

Total Pages: 202

ISBN-13: 3110473631

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In the field of organic semiconductors researchers and manufacturers are faced with a wide range of potential molecules. This work presents concepts for simulation-based predictions of material characteristics starting from chemical stuctures. The focus lies on charge transport – be it in microscopic models of amorphous morphologies, lattice models or large-scale device models. An extensive introductory review, which also includes experimental techniques, makes this work interesting for a broad readership. Contents: Organic Semiconductor Devices Experimental Techniques Charge Dynamics at Dierent Scales Computational Methods Energetics and Dispersive Transport Correlated Energetic Landscapes Microscopic, Stochastic and Device Simulations Parametrization of Lattice Models Drift–Diusion with Microscopic Link

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors
The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

Author: Carl. R Poelking

Publisher: Springer

Published: 2017-10-24

Total Pages: 142

ISBN-13: 3319695991

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This book focuses on the microscopic understanding of the function of organic semiconductors. By tracing the link between their morphological structure and electronic properties across multiple scales, it represents an important advance in this direction. Organic semiconductors are materials at the interface between hard and soft matter: they combine structural variability, processibility and mechanical flexibility with the ability to efficiently transport charge and energy. This unique set of properties makes them a promising class of materials for electronic devices, including organic solar cells and light-emitting diodes. Understanding their function at the microscopic scale – the goal of this work – is a prerequisite for the rational design and optimization of the underlying materials. Based on new multiscale simulation protocols, the book studies the complex interplay between molecular architecture, supramolecular organization and electronic structure in order to reveal why some materials perform well – and why others do not. In particular, by examining the long-range effects that interrelate microscopic states and mesoscopic structure in these materials, the book provides qualitative and quantitative insights into e.g. the charge-generation process, which also serve as a basis for new optimization strategies.

Effect of Encapsulation and Light-soak on Charge Transport Properties in Organic Semiconductor -based Diodes
Effect of Encapsulation and Light-soak on Charge Transport Properties in Organic Semiconductor -based Diodes

Author: Sanyasi Bobbara

Publisher:

Published: 2017

Total Pages: 0

ISBN-13:

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Organic semiconductors (OSs) have garnered a great attention in the recent years due to their ease of processibility, optical and electrical property-tunability, and to their cost-effectiveness. They form the class of materials most suitable for flexible electronics and bioelectronics, especially in association with solutionprocessable inorganic/hybrid materials. However, the charge mobility in these materials is strongly affected by their structural and energetic disorder introduced by the defects that 'trap' the charge carriers. Depending upon the physical location of the traps and their distribution in energy, they could significantly affect the charge transport in a device. The present work strives to probe the interface and bulk defect states in polymer-based diodes. In lieu of that, a part of the study involved characterizing the device with and without encapsulation, using techniques to record steady-state current-voltage (IV)behaviour, transients of charge extraction by linearly increasing voltage (CELIV) and dark-injection transient currents (DiTC), as well as photoluminescence (PL) and electroluminescence (EL) off the devices. The same characteristics have been carried out to observe the effect of ultra-violet (UV) lightsoak on the devices. All the tests were performed on three different polymers, namely P3HT, MDMO:PPV and PCDTBT. The comparison of the encapsulated versus unencapsulated devices gives an insight into characteristic differences in the measurables upon exposure to air and moisture. The light-soak tests indicate the modification of the cathode work function after a UV-assisted oxygen desorption off the polymer/cathode interface. A simultaneous effort went into an in-situ investigation of charge transport dynamics in organic semiconductors over wide time range at a microscopic scale.

Organic Field-Effect Transistors
Organic Field-Effect Transistors

Author: Zhenan Bao

Publisher: CRC Press

Published: 2018-10-03

Total Pages: 578

ISBN-13: 1351837575

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The remarkable development of organic thin film transistors (OTFTs) has led to their emerging use in active matrix flat-panel displays, radio frequency identification cards, and sensors. Exploring one class of OTFTs, Organic Field-Effect Transistors provides a comprehensive, multidisciplinary survey of the present theory, charge transport studies, synthetic methodology, materials characterization, and current applications of organic field-effect transistors (OFETs). Covering various aspects of OFETs, the book begins with a theoretical description of charge transport in organic semiconductors at the molecular level. It then discusses the current understanding of charge transport in single-crystal devices, small molecules and oligomers, conjugated polymer devices, and charge injection issues in organic transistors. After describing the design rationales and synthetic methodologies used for organic semiconductors and dielectric materials, the book provides an overview of a variety of characterization techniques used to probe interfacial ordering, microstructure, molecular packing, and orientation crucial to device performance. It also describes the different processing techniques for molecules deposited by vacuum and solution, followed by current technological examples that employ OTFTs in their operation. Featuring respected contributors from around the world, this thorough, up-to-date volume presents both the theory behind OFETs and the latest applications of this promising technology.