Tuning The Optical, Charge Injection, and Charge Transport Properties of Organic Electronic Devices

Since the early 1900's, synthetic insulating polymers (plastics) have slowly taken over the role that traditional materials like wood or metal have had as basic components for construction, manufactured goods, and parts. Plastics allow for high throughput, low temperature processing, and control of bulk properties through molecular modifications. In the same way, pi-conjugated organic molecules are emerging as a possible substitute for inorganic materials due to their electronic properties. The semiconductive nature of pi-conjugated materials make them an attractive candidate to replace inorganic materials, primarily due to their promise for low cost and large-scale production of basic semiconducting devices such as light-emitting diodes, solar cells, and field-effect transistors.Before organic semiconductors can be realized as a commercial product, several hurdles must be cleared. The purpose of this dissertation is to address three distinct properties that dominate the functionality of devices harnessing these materials: (1) optical properties, (2) charge injection, and (3) charge transport. First, it is shown that the electron injection barrier in the emissive layer of polymer light-emitting diodes can be significantly reduced by processing of novel conjugated oligoelectrolytes or deoxyribonucleic acid atop the emissive layer. Next, the charge transport properties of several polymers could be modified by processing them from solvents containing small amounts of additives or by using regioregular and enantiopure chemical structures. It is then demonstrated that the optical and electronic properties of Lewis basic polymer structures can be readily modified by interactions with strongly electron-withdrawing Lewis acids. Through red-shifted absorption, photoluminescence, and electroluminescence, a single pi-conjugated backbone can be polychromatic. In addition, interaction with Lewis acids can remarkably p-dope the hole transport of the parent polymer, leading to a two-orders of magnitude increase in the hole mobility. Finally, the hole, electron, and double carrier transport in solar cell devices are studied in a bid to examine the correlations between bulk morphologies and free carrier recombination.The sum of these works help to create new pathways for the synthesis and design of new pi-conjugated materials and device architectures. All of this is in hopes of achieving higher performance and more stable devices to rival inorganic systems

A Janus Molecule for Screen-Printable Conductive Carbon Ink for Composites with Superior Stretchability

Inspired by decades of research in the compatibilization of fillers into elastomeric composites for high-performance materials, a novel polyurethane-based stretchable carbon ink is created by taking advantage of a Janus molecule, 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol (serinol pyrrole, SP). SP is used to functionalize the carbon and comonomer in the polymer phase. The use of SPs in both the organic and inorganic phases results in an improved interaction between the two phases. When printed, the functionalized material has a factor 1.5 lower resistance-strain dependence when compared to its unfunctionalized analogue. This behavior is superior to commercially available carbon inks. To demonstrate the suitability of ink in an industrial application, an all-printed, elastomer-based force sensor is fabricated. This “pyrrole methodology” is scalable and broadly applicable, laying the foundation for the realization of printed functionalities with improved electromechanical performance.</p

Optimization of energy levels by molecular design: evaluation of bis-diketopyrrolopyrrole molecular donor materials for bulk heterojunction solar cells

We report a series of solution-processable, small-molecule, donor materials based on an architecture consisting of two diketopyrrolopyrrole (DPP) cores with different aromatic pi-bridges between the DPP units and different end-capping groups. In general, this architecture leads to desirable light absorption and electronic levels for donor materials. Out of the compounds investigated, a material with a hydrolyzed dithieno(3,2-b;2',3'-d)silole (SDT) core and 2-benzofuran (BFu) end capping groups leads to the most favorable properties for solar cells, capable of generating photocurrent up to 800 nm while producing an open-circuit voltage of over 850 mV, indicating a small loss in electrical potential compared to other bulk heterojunction systems. Device properties can be greatly improved through the use of solvent additives such as 2-chloronaphthalene and initial attempts to optimize device fabrication have resulted in power conversion efficiencies upwards of 4%.close372

Porous PU/PEDOT:PSS electrodes for probing bioelectricity in Oscillatoria sp. Cohorts

Increasing frequency of poor water quality events associated with cyanobacteria strains capable of producing taste and odour (T&O) metabolites and toxins is a global concern for human health and the drinking water industry. This is mostly due to the inability of timely detecting and predicting cyanobacteria productivity associated with water quality risks. Here, we develop and characterize an ultra-sensitive electrophysiology system based on porous polyurethane (PU) foams coated with poly (3, 4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) exploiting large-area electrodes of 199 cm2, which maximizes the double-layer capacitance and concomitant detection sensitivity. The measured signal of the cyanobacteria model taxa Oscillatoria sp. results from the sum of all individual cell contributions and scales with electrode area, hence indicating correlation with productivity and biomass. Stochastic activity across the cohort is monitored as uncorrelated noise. Yet, when Oscillatoria sp. operate cooperatively, the signal appears as intercellular Ca2+ waves which are benchmarked with a conventional fluorescent probe and suppressed with the specific ion channel inhibitor gadolinium chloride. We suggest the existence of a paracrine signaling mechanism with Ca2+ acting as the chemical messenger across large cohorts that may prove to be linked with T&O metabolite 2-Methylisoborneol (2-MIB) production. The technology proposed here would enable in-situ real time monitoring of benthic cyanobacteria productivity and hence proxy data for their metabolite production. This paves the way for identifying sources of cyanobacteria metabolites including 2-MIB, geosmin and cyanotoxins, and hence identify intervention solutions and treatment optimization for removal of these detrimental metabolites

Tuning The Optical, Charge Injection, and Charge Transport Properties of Organic Electronic Devices

Since the early 1900's, synthetic insulating polymers (plastics) have slowly taken over the role that traditional materials like wood or metal have had as basic components for construction, manufactured goods, and parts. Plastics allow for high throughput, low temperature processing, and control of bulk properties through molecular modifications. In the same way, pi-conjugated organic molecules are emerging as a possible substitute for inorganic materials due to their electronic properties. The semiconductive nature of pi-conjugated materials make them an attractive candidate to replace inorganic materials, primarily due to their promise for low cost and large-scale production of basic semiconducting devices such as light-emitting diodes, solar cells, and field-effect transistors.Before organic semiconductors can be realized as a commercial product, several hurdles must be cleared. The purpose of this dissertation is to address three distinct properties that dominate the functionality of devices harnessing these materials: (1) optical properties, (2) charge injection, and (3) charge transport. First, it is shown that the electron injection barrier in the emissive layer of polymer light-emitting diodes can be significantly reduced by processing of novel conjugated oligoelectrolytes or deoxyribonucleic acid atop the emissive layer. Next, the charge transport properties of several polymers could be modified by processing them from solvents containing small amounts of additives or by using regioregular and enantiopure chemical structures. It is then demonstrated that the optical and electronic properties of Lewis basic polymer structures can be readily modified by interactions with strongly electron-withdrawing Lewis acids. Through red-shifted absorption, photoluminescence, and electroluminescence, a single pi-conjugated backbone can be polychromatic. In addition, interaction with Lewis acids can remarkably p-dope the hole transport of the parent polymer, leading to a two-orders of magnitude increase in the hole mobility. Finally, the hole, electron, and double carrier transport in solar cell devices are studied in a bid to examine the correlations between bulk morphologies and free carrier recombination.The sum of these works help to create new pathways for the synthesis and design of new pi-conjugated materials and device architectures. All of this is in hopes of achieving higher performance and more stable devices to rival inorganic systems

Proper local wireless network signal planning procedures for real coverage achievement

Diplomsko delo obravnava perečo problematiko pri načrtovanju nelicenčnega lokalnega brezžičnega omrežja s pomočjo programske podpore in neustreznost s poznejšim resničnim stanjem pokritosti. Pri tem se je potrebno zavedati, da v fazi načrtovanja marsikateri objekt še ne obstaja. Diplomsko delo je vsebinsko in strukturno razdeljeno na tri poglavja. V prvem poglavju so opisani trenutno uporabljani nelicenčni brezžični standardi. Opisani so načini pristopov za načrtovanje v dvorazsežnem (2D) in trirazsežnem (3D) prostoru. Naveden je cilj pričujočega diplomskega dela, ki ugotavlja neustreznost med načrtovanim in poznejšim resničnim stanjem pokritosti z brezžičnim signalom v trirazsežnem (3D) prostoru V drugem poglavju so opisane tehnične značilnosti programskega orodja in ustrezne značilnosti dostopovnih točk, ki omogočajo načrtovanje v trirazsežnem (3D) prostoru. Umeščanje tipskega slabljenja sten in stropov v programsko orodje posledično pomeni slab rezultat pokritosti v resnični stavbi V tretjem poglavju so predstavljeni pravilni pristopi k meritvam slabljenja sten in stropov, prav tako pa je predstavljen tudi pravilno načrtovan objekt z manjšim odstopanjem od resničnega stanja. Ugotovljeno je, da je namen diplomskega dela dosežen, ker omogoča že v postopku načrtovanja neobstoječega objekta z več kot 95% zanesljivostjo, da se predvidi resnična pokritost z brezžičnim signalom.Thesis deals with the delicate issue in the design of unlicensed wireless local network through software support and a concequently inappropriate result of real site survey coverage. Lots of buildings do not exist in the moment of planning stage. The thesis is divided into three sections: The first chapter describes the currently used unlicensed wireless standards. Methods of different approaches are described to design two dimesional (2D) and three dimesional (3D) spaces. Aim of thessis is summarized in conclusion of unadequate result between planned and real wireless signal coverage in three dimesional (3D) space. The second chapter describes the technical characteristics of the software and the relevant characteristics of the access points, enabling the design in three dimesional (3D) space. Positioning using software\u27s general attenuation of walls and ceilings tool consequently means a bad score coverage in a real building In the third chapter proper approach to measuring the attenuation of walls and ceilings is presented and properly designed facility with minor deviations from real site survey is shown. It is noted that the purpose of the thessis is completed, because it allows a confidence of more than 95% prediction of real coverage of the wireless signal in the process of planning a nonexistent building

Engineering the Comfort‐of‐Wear for Next Generation Wearables

Abstract Wearable technologies are becoming important for the fields of information technology and healthcare, driven mainly by societal issues such as the aging society and the current pandemic. Recently developed flexible/stretchable wearable devices have demonstrated their ability for long‐term healthcare monitoring with improved signal integrity and multimodality. However, the adherence of wearers to such wearable devices cannot be determined only by the function. Here “comfort‐of‐wear” is identified as one of the most critical parameters for future wearables, similar to how clothes are chosen based on how comfortable they are. “Comfort‐of‐wear” is defined as the device's ability to not to disturb the wearers’ daily life. Several engineering approaches are introduced to improve the comfort‐of‐wear of devices—via strategies that include improving flexibility by utilizing a combination of structures, materials, and systems. Finally, the future of wearables enabled by cutting‐edge advanced electronic technologies is proposed

Dual-gate organic phototransistor with high-gain and linear photoresponse

High-resolution imaging technologies call for photodetectors with high-gain and linear response over a large dynamic range. Chow et al. show a dual-gate structure that combines the operation of photodiodes and phototransistors to enable both amplified and linear response without external circuitry

Active-matrix IGZO array with printed thermistor for large-area thermal imaging

\u3cp\u3eThermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution.\u3c/p\u3

Active-matrix IGZO array with printed thermistor for large-area thermal imaging

Thermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution