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Inkjet-Printed Light-Emitting Devices: Applying Inkjet Microfabrication to Multilayer Electronics

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Inkjet-Printed Light-Emitting Devices: Applying Inkjet Microfabrication to Multilayer Electronics Inkjet-Printed Light-Emitting Devices: Applying Inkjet Microfabrication to Multilayer Electronics by Peter D. Angelo A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Chemical Engineering & Applied Chemistry University of Toronto Copyright by Peter David Angelo 2013 Inkjet-Printed Light-Emitting Devices: Applying Inkjet Microfabrication to Multilayer Electronics Peter D. Angelo Doctor of Philosophy Department of Chemical Engineering & Applied Chemistry University of Toronto 2013 Abstract This work presents a novel means of producing thin-film light-emitting devices, functioning according to the principle of electroluminescence, using an inkjet printing technique. This study represents the first report of a light-emitting device deposited completely by inkjet printing. An electroluminescent species, doped zinc sulfide, was incorporated into a polymeric matrix and deposited by piezoelectric inkjet printing. The layer was printed over other printed layers including electrodes composed of the conductive polymer poly(3,4-ethylenedioxythiophene), doped with poly(styrenesulfonate) (PEDOT:PSS) and single-walled carbon nanotubes, and in certain device structures, an insulating species, barium titanate, in an insulating polymer binder. The materials used were all suitable for deposition and curing at low to moderate (<150°C) temperatures and atmospheric pressure, allowing for the use of polymers or paper as supportive substrates for the devices, and greatly facilitating the fabrication process. ii The deposition of a completely inkjet-printed light-emitting device has hitherto been unreported. When ZnS has been used as the emitter, solution-processed layers have been prepared by spin- coating, and never by inkjet printing. Furthermore, the utilization of the low-temperature- processed PEDOT:PSS/nanotube composite for both electrodes has not yet been reported. Device performance was compromised compared to conventionally prepared devices. This was partially due to the relatively high roughness of the printed films. It was also caused by energy level misalignment due to quantization (bandgap widening) of the small (<10 nm) nanoparticles, and the use of high work function cathode materials (Al and PEDOT:PSS). Regardless of their reduced performance, inkjet printing as a deposition technique for these devices presents unique advantages, the most notable of which are rapidity of fabrication and patterning, substrate flexibility, avoidance of material wastage by using drop-on-demand technology, and the need for only one main unit operation to produce an entire device. iii Acknowledgements The Pulp & Paper Centre in the Department of Chemical Engineering & Applied Chemistry at the University of Toronto has provided me with an environment in which I have been able to develop and refine both my project and my understanding of the fundamentals of chemical and materials engineering. The Department, the Estate of W.H Rapson, the School of Graduate Studies, the University of Toronto, the SENTINEL Bioactive Paper Network, and the Government of Ontario have all financially supported my continued perseverance in my doctoral studies, and I am deeply grateful to each. I would also like to acknowledge the generosity and companionship of all my colleagues within the Pulp & Paper laboratories and other laboratory groups within the Department. My understanding of several new aspects of chemical engineering was also deepened by my supervising committee members, Dr. Edgar Acosta and Dr. Timothy Bender. The laboratory of Dr. Ning Yan in the Faculty of Forestry was particularly welcoming, and always willing to provide access to both analytical equipment and technical expertise. The encouragement of my supervisor, Dr. Ramin Farnood, has been instrumental in keeping me focused on my work. His continued forward drive and enthusiasm, as well as all of the knowledge he has readily imparted to me, have led me to the successful conclusion of this long process. I feel very fortunate to have worked with such a helpful and driven person. My family’s perpetual support has buoyed me from the first day of my degree and throughout. I cannot express my thanks sufficiently to them for their love and help. My father’s ready willingness to discuss my work and give advice taken from his long-time familiarity with electrical engineering has given me insight and inspiration on many occasions. Finally, my wife Emily has kept me level, confident, and determined throughout my studies, while bringing me joy each and every day. Her love has made persevering to the end worth every moment spent, and taught me to look to the future with excitement and hope. iv Nomenclature Abbreviations 2D two-dimensional 3D three-dimensional AC alternating current AFM atomic force microscopy ALD atomic layer deposition ASTM American Society for Testing & Materials BSE backscattered electron CRT cathode ray tube CVD chemical vapour deposition DC direct current DLS dynamic light scattering DOD drop-on-demand DPI dots per square inch EL electroluminescence ELD electroluminescent display FPD flat-panel display HOMO highest occupied molecular orbital IR infrared LED light-emitting device/diode LUMO lowest unoccupied molecular orbital OLED organic light-emitting diode/device PDP plasma display panel PEL powder electroluminescent device PL photoluminescence PLE photoluminescent excitation PVD physical vapour deposition QD quantum dot R2R roll-to-roll SEM scanning electron microscope TAPPI Technical Association of the Pulp & Paper Industry TEM transmission electron microscope TFEL thin-film electroluminescent device TFT thin-film transistor ToF-SIMS time-of-flight secondary ion mass spectrometry UV ultraviolet XRD X-ray diffraction v Terminology dynamic viscosity (cP) surface tension/energy (mN/m) zeta-potential (mV) dp particle diameter (nm) dielectric constant (unitless) resistivity ( m) R resistance () conductivity (S/cm) wavelength (nm) c contact angle (°) Oh Ohnesorge number (unitless) Z-1 inverse Ohnesorge number (unitless) En Energy number (unitless) V voltage (V) I current (A) C capacitance (F) Eg energy band gap (eV) work function (eV) L luminance (cd/m2) luminous efficiency (lm/W) M molarity (mol/L) Mw polymer molecular weight (g/mol) h Planck’s constant (4.13566733 × 10−15 eV·s) ħ reduced Planck’s constant (6.58211899 × 10−16 eV·s) −12 0 vacuum permittivity (8.854187817620 × 10 F/m) 8 c speed of light (2.99792458 × 10 m/s) vi Materials 3-MPA 3-mercaptopropionic acid AA acrylic acid - Ac acetate ion (CH3COO ) AKD alkylketene dimer ATO antimony tin oxide C60 fullerene CdS cadmium sulfide CdSe cadmium selenide DMSO dimethyl sulfoxide HW hardwood ITO indium tin oxide MMA methyl methacrylate MWCNT multi-walled carbon nanotube PAA polyacrylic acid PAc polyacetylene PAni polyaniline PDADMAC poly(diallyldimethylammonium chloride) PEDOT poly(3,4-ethylenedioxythiophene) PEDOT:PSS poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) PEG polyethylene glycol PEI poly(ethyleneimine) PET polyethylene PMMA poly(methyl methacrylate) PPV poly(p-phenylene vinylene) PPy polypyrrole PT polythiophene PTFE polytetrafluoroethylene (Teflon) PVDF polyvinylidene fluoride PVK poly(N-vinylcarbazole) PVP polyvinylpyrrolidone SHMP sodium hexametaphosphate SLS sodium lauryl sulfate SW softwood SWCNT single-walled carbon nanotube TGA thioglycolic acid S-SWCNT ultra-short single-walled carbon nanotube ZnS:X doped zinc sulfide, X being dopant atom vii Units a.u. arbitrary units at. % atomic percentage wt. % weight percentage, weight basis vol. % volume percentage, volume basis mol. % molar percentage, molar basis VAC alternating current voltage VDC direct current voltage RPM revolutions per minute / ohm/square, sheet resistance for a square sample viii Table of Contents Acknowledgements ........................................................................................................................ iv Nomenclature .................................................................................................................................. v Table of Contents ........................................................................................................................... ix List of Figures .............................................................................................................................. xiv List of Tables ................................................................................................................................ xx List of Appendices ....................................................................................................................... xxi List of Original Papers ................................................................................................................ xxii Chapter 1 ......................................................................................................................................... 1 1 Introduction ................................................................................................................................ 1 1.1 Motivation ........................................................................................................................... 4 1.2 Related work on printed LEDs ........................................................................................... 6 1.3 Approach ............................................................................................................................. 9 1.4 Thesis
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