The Stretchable OLED Display

Documenting the evolution of flexible and stretchable electronics, this thesis highlights the shift from traditional circuits to innovative designs that leverage materials like organic semiconductors and advanced substrates for enhanced mechanical, optical, and electrical properties.Recent advancements in flexible electronics, primarily due to effective management of bending strain, have unlocked diverse applications including wearable technology, flexible solar cells, bio-integrated devices, and notably, stretchable organic displays, with the latter being a focal point of this project. While bendable designs have successfully entered commercial production, the development of stretchable applications continues to pose significant challenges.The focus here is on optimizing each element of organic light-emitting diodes, from elastomeric substrates and electrodes to active organic layers, balancing performance with cost-effectiveness for potential mass production. In particular, this project leverages a novel surface design to enhance the stretchability of thin film devices. Through the utilization of microscopic surface waves molded on substrates, thin films applied are subjected to reduced stress, when the devices are stretched, as the designed waves convert tensile into bending strain.The effect is documented numerically and experimentally on substrate and thin film level. The deposition process for indium tin oxide was optimized to ensure homogeneous, defect-free thin films that seamlessly conform to the contours of the surface design. Experimentally, these high performance inorganic electrodes endure a three-fold increased stretch, when stretching devices with the incorporated surface design, relative to planar counterparts. The report focuses intensively on outcomes, emphasizing the experimental methodologies and essential processes uncovered in the pursuit of creating thin film devices that adapt seamlessly to the designed surface contour.The substrates are produced using doctor-blade coating, while the thin films are deposited through processes like magnetron sputtering and evaporation techniques. Each process is investigated and optimized utilizing an extensive collection of characterization tools. This includes sophisticated, conventional, and project-specifically developed equipment, encompassing techniques like atomic force microscopy, scanning electron microscopy, gallium focused ion beam helium ion microscopy, and grazing incidence x-ray diffraction, alongside optical, electrical, and custom-built in situ electro-mechanical characterization systems. Additionally, the project utilizes finite element models for the numerical quantification of mechanical properties and in assessing the efficiency of organic semiconductor devices.This project has successfully achieved the creation and characterization of functional light-emitting diodes on the stretchable substrates utilizing the intended surface wave design. These have been compared to their counterparts on rigid substrates, displaying comparable, though slightly lower, current efficiencies. However, the tensile characterization of these devices in operando has not been accomplished in this phase of the project.In conclusion, this thesis underscores advancements and challenges in the ongoing journey towards the realization of fully functional stretchable organic light-emitting diode displays. Examining each aspect of the devices, from substrates to active layers and interconnects, is a methodical approach for in-depth research going forward, and crucial for addressing specific challenges and fostering innovation, paving the way for promising breakthroughs in stretchable electronics.Documenting the evolution of flexible and stretchable electronics, this thesis highlights the shift from traditional circuits to innovative designs that leverage materials like organic semiconductors and advanced substrates for enhanced mechanical, optical, and electrical properties.Recent advancements in flexible electronics, primarily due to effective management of bending strain, have unlocked diverse applications including wearable technology, flexible solar cells, bio-integrated devices, and notably, stretchable organic displays, with the latter being a focal point of this project. While bendable designs have successfully entered commercial production, the development of stretchable applications continues to pose significant challenges.The focus here is on optimizing each element of organic light-emitting diodes, from elastomeric substrates and electrodes to active organic layers, balancing performance with cost-effectiveness for potential mass production. In particular, this project leverages a novel surface design to enhance the stretchability of thin film devices. Through the utilization of microscopic surface waves molded on substrates, thin films applied are subjected to reduced stress, when the devices are stretched, as the designed waves convert tensile into bending strain.The effect is documented numerically and experimentally on substrate and thin film level. The deposition process for indium tin oxide was optimized to ensure homogeneous, defect-free thin films that seamlessly conform to the contours of the surface design. Experimentally, these high performance inorganic electrodes endure a three-fold increased stretch, when stretching devices with the incorporated surface design, relative to planar counterparts. The report focuses intensively on outcomes, emphasizing the experimental methodologies and essential processes uncovered in the pursuit of creating thin film devices that adapt seamlessly to the designed surface contour.The substrates are produced using doctor-blade coating, while the thin films are deposited through processes like magnetron sputtering and evaporation techniques. Each process is investigated and optimized utilizing an extensive collection of characterization tools. This includes sophisticated, conventional, and project-specifically developed equipment, encompassing techniques like atomic force microscopy, scanning electron microscopy, gallium focused ion beam helium ion microscopy, and grazing incidence x-ray diffraction, alongside optical, electrical, and custom-built in situ electro-mechanical characterization systems. Additionally, the project utilizes finite element models for the numerical quantification of mechanical properties and in assessing the efficiency of organic semiconductor devices.This project has successfully achieved the creation and characterization of functional light-emitting diodes on the stretchable substrates utilizing the intended surface wave design. These have been compared to their counterparts on rigid substrates, displaying comparable, though slightly lower, current efficiencies. However, the tensile characterization of these devices in operando has not been accomplished in this phase of the project.In conclusion, this thesis underscores advancements and challenges in the ongoing journey towards the realization of fully functional stretchable organic light-emitting diode displays. Examining each aspect of the devices, from substrates to active layers and interconnects, is a methodical approach for in-depth research going forward, and crucial for addressing specific challenges and fostering innovation, paving the way for promising breakthroughs in stretchable electronics.<br/

Stretchable substrates with 3D wave patterned surface for enhanced mechanical stability of indium tin oxide electrodes

Flexible electronic devices have promising applications in many future technologies such as wearables, implantables, robotics, and displays. Among the distinct types of mechanical flexibility, stretchability stands as a significant challenge. A particularly demanding objective is the realization of a high-performance transparent electrode that endures stretching and can be mass produced, all while avoiding additional restrictions on device density. In this work, it is demonstrated that a 3D wave patterned surface provides a threefold improved strain performance of deposited indium tin oxide electrodes, in a statistical comparison of 3D wave patterned and planar surfaces, where indium tin oxide electrodes are stretched to electrical failure. Moreover, this platform alleviates residual thin film stress, allowing for easier handling of the substrates. This study demonstrates the feasibility of attaining stretchability for upcoming electronic devices using a scalable platform that incorporates high-performance transparent electrode materials using only conventional materials and fabrication steps.</p

Interference in edge-scattering from monocrystalline gold flakes

We observe strongly dissimilar scattering from two types of edges in hexagonal quasi-monocrystalline gold flakes with thicknesses around 1 micron. We identify as the origin the interference between a direct, quasi-specular scattering and an indirect scattering process involving an intermediate surface-plasmon state. The dissimilarity between the two types of edges is a direct consequence of the three-fold symmetry around the [111]-axis and the intrinsic chirality of a face-centered cubic lattice. We propose that this effect can be used to estimate flake thickness, crystal morphology, and surface contamination

Structural Evaluation of 5,5′-Bis(naphth-2-yl)-2,2′-bithiophene in Organic Field-Effect Transistors with n-Octadecyltrichlorosilane Coated SiO₂ Gate Dielectric

We report on the structure and morphology of 5,5′-bis(naphth-2-yl)-2,2′-bithiophene (NaT2) films in bottom-contact organic field-effect transistors (OFETs) with octadecyltrichlorosilane (OTS) coated SiO 2 gate dielectric, characterized by atomic force microscopy (AFM), grazing-incidence X-ray diffraction (GIXRD), and electrical transport measurements. Three types of devices were investigated with the NaT2 thin-film deposited either on (1) pristine SiO 2 (corresponding to higher surface energy, 47 mJ/m 2) or on OTS deposited on SiO 2 under (2) anhydrous or (3) humid conditions (corresponding to lower surface energies, 20-25 mJ/m 2). NaT2 films grown on pristine SiO 2 form nearly featureless three-dimensional islands. NaT2 films grown on OTS/SiO 2 deposited under anhydrous conditions form staggered pyramid islands where the interlayer spacing corresponds to the size of the NaT2 unit cell. At the same time, the grain size measured by AFM increases from hundreds of nanometers to micrometers and the crystal size measured by GIXRD from 30 nm to more than 100 nm. NaT2 on OTS/SiO 2 deposited under humid conditions also promotes staggered pyramids but with smaller crystals 30-80 nm. The NaT2 unit cell parameters in OFETs differ 1-2% from those in bulk. Carrier mobilities tend to be higher for NaT2 layers on SiO 2 (2-3 × 10 -4 cm 2/(V s)) compared to NaT2 on OTS (2 × 10 -5-1 × 10 -4 cm 2/(V s)). An applied voltage does not influence the unit cell parameters when probed by GIXRD in operando. </p

Falcarindiol purified from carrots leads to elevated levels of lipid droplets and upregulation of peroxisome proliferator-activated receptor-γ gene expression in cellular models

Falcarindiol (FaDOH) is a cytotoxic and anti-inflammatory polyacetylenic oxylipin found in food plants of the carrot family (Apiaceae). FaDOH has been shown to activate PPARγ and to increase the expression of the cholesterol transporter ABCA1 in cells, both of which play an important role in lipid metabolism. Thus, a common mechanism of action of the anticancer and antidiabetic properties of FaDOH may be due to a possible effect on lipid metabolism. In this study, the effect of sub-toxic concentration (5 μM) of FaDOH inside human mesenchymal stem cells (hMSCs) was studied using white light microscopy and Raman imaging. Our results show that FaDOH increases lipid content in the hMSCs cells as well as the number of lipid droplets (LDs) and that this can be explained by increased expression of PPARγ2 as shown in human colon adenocarcinoma cells. Activation of PPARγ can lead to increased expression of ABCA1. We demonstrate that ABCA1 is upregulated in colorectal neoplastic rat tissue, which indicates a possible role of this transporter in the redistribution of lipids and increased formation of LDs in cancer cells that may lead to endoplasmic reticulum stress and cancer cell death

The Stretchable OLED Display

Documenting the evolution of flexible and stretchable electronics, this thesishighlights the shift from traditional circuits to innovative designs that leveragematerials like organic semiconductors and advanced substrates for enhancedmechanical, optical, and electrical properties.Recent advancements in flexible electronics, primarily due to effective management of bending strain, have unlocked diverse applications including wearabletechnology, flexible solar cells, bio-integrated devices, and notably, stretchableorganic displays, with the latter being a focal point of this project. While bendabledesigns have successfully entered commercial production, the development ofstretchable applications continues to pose significant challenges.The focus here is on optimizing each element of organic light-emitting diodes,from elastomeric substrates and electrodes to active organic layers, balancingperformance with cost-effectiveness for potential mass production. In particular,this project leverages a novel surface design to enhance the stretchability of thinfilm devices. Through the utilization of microscopic surface waves molded onsubstrates, thin films applied are subjected to reduced stress, when the devicesare stretched, as the designed waves convert tensile into bending strain.The effect is documented numerically and experimentally on substrate andthin film level. The deposition process for indium tin oxide was optimizedto ensure homogeneous, defect-free thin films that seamlessly conform to thecontours of the surface design. Experimentally, these high performance inorganicelectrodes endure a three-fold increased stretch, when stretching devices withthe incorporated surface design, relative to planar counterparts. The reportfocuses intensively on outcomes, emphasizing the experimental methodologiesand essential processes uncovered in the pursuit of creating thin film devicesthat adapt seamlessly to the designed surface contour.The substrates are produced using doctor-blade coating, while the thin filmsare deposited through processes like magnetron sputtering and evaporationtechniques. Each process is investigated and optimized utilizing an extensivecollection of characterization tools. This includes sophisticated, conventional,and project-specifically developed equipment, encompassing techniques likeatomic force microscopy, scanning electron microscopy, gallium focused ionbeam helium ion microscopy, and grazing incidence x-ray diffraction, alongsideoptical, electrical, and custom-built in situ electro-mechanical characterizationsystems. Additionally, the project utilizes finite element models for the numericalquantification of mechanical properties and in assessing the efficiency of organicsemiconductor devices.This project has successfully achieved the creation and characterization offunctional light-emitting diodes on the stretchable substrates utilizing the intended surface wave design. These have been compared to their counterparts onrigid substrates, displaying comparable, though slightly lower, current efficiencies. However, the tensile characterization of these devices in operando has notbeen accomplished in this phase of the project.In conclusion, this thesis underscores advancements and challenges in theongoing journey towards the realization of fully functional stretchable organiclight-emitting diode displays. Examining each aspect of the devices, from substrates to active layers and interconnects, is a methodical approach for in-depthresearch going forward, and crucial for addressing specific challenges and fostering innovation, paving the way for promising breakthroughs in stretchableelectronics

Stress-distributing layer for improved stretchability of thin-films on soft substrates with corrugated surfaces

A flexible thin-film device (10) comprising - a flexible polymer substrate (5) comprising a corrugated surface structure (8) comprising a pattern of waves, the waves following one or more curved lines and/or one or more straight lines; - one or more functional layers (7) on the corrugated surface structure (8), the one or more functional layers (7) defining an upper surface (9) opposite to the corrugated surface structure (8); and - a stress-distribution layer (6) comprising a flexible polymer layer on the upper surface (9).</p

Transparent and conductive electrodes by large-scale nanostructuring of noble metal thin-films

The widespread use of transparent conductive films in modern display and solar technologies calls for engineering solutions with tunable light transmission and electrical characteristics. Currently, considerable effort is put into the optimization of indium tin oxide, carbon nanotube-based, metal grid, and nano-wire thin-films [1]. The indium and carbon films do not match the chemical stability nor the electrical performance of the noble metals, and many metal films are not uniform in material distribution leading to significant surface roughness and randomized transmission haze. We demonstrate solution-processed masks for physical vapor-deposited metal electrodes consisting of hexagonally ordered aperture arrays with scalable aperture-size and spacing in an otherwise homogeneous noble metal thin-film. The fabricated electrodes are characterized optically and electrically by measuring transmittance and sheet resistance. The presented methods yield large-scale reproducible results. Experimentally realized thin-films show good agreement with finite-element method simulations and an analytical model of sheet resistance in thin-films with ordered apertures support the experimental results and serve to aid the design of highly transparent conductive films. A maximum Haacke number for these 33 nm thin-films, ΦH = 10.7×10−3Ω−1, equivalent to T≃80 % and Rsh≃10 Ω/sq, is extrapolated from the theoretical results. This corresponds to better electrical performance than carbon nanotube-based thin-films for equivalent optical transparency. Increased transparency may be realizable using thinner metal films trading off conductivity. Nevertheless, the findings of this article indicate that colloidal lithographic patterned transparent conductive films can serve as vital components in technologies with a demand for transparent electrodes with low sheet resistance

Gap‐Surface Plasmon Metasurfaces for Broadband Circular‐to‐Linear Polarization Conversion and Vector Vortex Beam Generation

The ability to control and manipulate the polarization state of light is of crucial importance in many modern optical applications ranging from quantum technologies to biomedical sciences. Here, an ultrathin quarter‐wave plate (QWP) with a gap‐surface plasmon metasurface is designed, fabricated, and experimentally demonstrated, allowing for broadband and efficient conversion between circular and linear polarizations with ≈85% average reflectance across a 200 nm wide bandwidth in the near‐infrared range (750–950 nm). Based on the QWP design, a general method is further derived to generate vector vortex beams (VVBs) that possess spatially varied distributions of the polarization vector and carry specified orbital angular momentums by using space‐variant QWP unit cells. The fabricated metasurface exhibits highly efficient VVB generation over a wavelength range from 750 to 950 nm, with average efficiencies of ≈72% and ≈68% for the right circularly polarized and left circularly polarized incident light, respectively. The developed approach allows compact, cost‐effective, and high‐performance polarization converters to be realized, paving the way for the ultimate miniaturization of optical devices with arbitrary control of light fields

Structural basis for a naphthyl end-capped oligothiophene with embedded metallic nanoparticles for organic field-effect transistors

We report on the apparent structure of 5,5″-bis(naphth-2-yl)-2,2′:5′,2″-terthiophene (NaT3) in organic field-effect transistors (OFETs) with and without embedded silver nanoparticles. Using regular- and microbeam grazing incidence wide- and small-angle X-ray scattering, the device structure is characterized locally in the area with the embedded particles. The NaT3 thin film order is reduced and the found unit cell (a = 25.7 Å, b = 5.87 Å, c = 8.03 Å, and β = 98.9°) differs significantly from the one reported in the bulk, but shows no significant change, when the particles corresponding to the crystal size are incorporated into the device structure. At the same time, the apparent thin film crystal sizes in OFETs are found to be similar with and without the embedded particles. In both cases, the carrier mobilities are of the order of 10$^{−4}$ cm$^2$/(V s)