- AutorIn
- Cecilia Teixeira da Rocha
- Titel
- Improved Organic Semiconductor Thin-Film Formation through the Addition of Vibrations to the Solution Shearing Method
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-718281
- Datum der Einreichung
- 13.09.2019
- Datum der Verteidigung
- 23.06.2020
- Abstract (EN)
- In this thesis, methods for improving charge carrier mobility and deposition conditions for the solution shearing of organic semiconductors for organic field-effect transistors (OFETs) are investigated. Electrical performance for OFETs is currently still limited by the charge carrier mobility, especially when high fabrication speeds are required. In this work, adaptations are made to the solution shearing method to enhance charge carrier mobility values and to increase the deposition speed and film uniformity of semiconductor films. The solution shearing method can be easily adapted to large-scale roll-to-roll fabrication, a low-cost and high throughput fabrication process. In this work, the fabrication of OFETs with both crystalline small-molecule and donor-acceptor polymer semiconductors as the active layer is performed, and significant improvements in charge carrier mobility and film formation are achieved. Specifically, the crystalline small-molecule semiconductor TIPS-pentacene is blended with the inert dielectric polystyrene, and solution shearing parameters are optimized to obtain highly-aligned crystalline films. The thin film with optimized morphology is deposited on a very thin polymer dielectric film, demonstrating the feasibility of high-performance OFETs (effective mobility of ~1.2 cm2 V-1s-1) and an ultra-low operating voltage (~1 V) – at the time a record value. To improve crystal growth, the solution shearing method is modified to add vibrations to the liquid during the coating process. The new coating method, named “piezoshearing”, allows the application of vibrations to the liquid during deposition through the attachment of a piezo actuator to the shearing blade. The piezoshearing is implemented to enhance crystal growth during the solution shearing of crystalline materials, and tests of piezoshearing for the material 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) demonstrate that substrate coverage can be increased due to induced stick-and-slip caused by the piezoshearing. Due to the unfavorable wetting conditions of semiconducting donor-acceptor polymer solutions on the commonly used low surface energy OFET substrates, conventional solution shearing is problematic. With piezoshearing, film deposition can be significantly improved. In particular, through piezoshearing the so-called stick-and-slip instabilities are mitigated, allowing the doubling of the shearing speed, and the deposition of smooth and ultrathin films (~7 nm). In addition to enabling higher coating speeds, piezoshearing also lowers the polymer material consumption by up to ~ 70% in comparison to the conventional solution shearing method. For some materials, piezoshearing is also found to increase the charge carrier mobility in OFET devices by up to two orders of magnitude. The piezoshearing is utilized for viscous polymer solutions, which are challenging to coat, and usually, result in non-uniform films. Three donor-acceptor polymer systems were tested, and morphology changes are observed for all materials when piezoshearing is applied. For one of the polymeric solutions, an increase in crystallinity is achieved, possibly accompanied by a change in the degree of alignment of the polymer chains. For two other polymer solutions with higher molecular weight chains, very smooth films were obtained with the piezoshearing – saving 30% of material. Without the application of vibrations, such materials yield very non-uniform films, with significant thickness variations, which is unsuitable for OFET devices. In summary, this work leads to significant improvements in the solution shearing of organic semiconductor materials by adding vibrations in the kHz range to the deposition process. The effects and benefits of utilizing the piezoshearing are demonstrated, and suggestions for further improvement and studies are made.
- Verweis
- Mitigating Meniscus Instabilities in Solution-Sheared Polymer Films for Organic Field-Effect Transistors
DOI: 10.1021/acsami.9b07832 - Solution Coating of Small Molecule/Polymer Blends Enabling Ultralow Voltage and High-Mobility Organic Transistors
DOI: 10.1002/aelm.201800141 - High-Mobility, Solution-Processed Organic Field-Effect Transistors from C8-BTBT:Polystyrene Blends
DOI: 10.1002/aelm.201800076 - Freie Schlagwörter (EN)
- Organic Field-Effect Transistor, Solution shearing, Organic semiconductors, Thin film uniformity, Shearing with vibration
- Klassifikation (DDC)
- 621.3
- Klassifikation (RVK)
- ZN 4870
- GutachterIn
- Prof. Dr. Stefan C. B. Mannsfeld
- Prof. Dr. Francisco Molina-Lopez
- Prof. Dr. sc. techn. habil. Frank Ellinger
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-718281
- Veröffentlichungsdatum Qucosa
- 02.09.2020
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
- CC BY 4.0
- Inhaltsverzeichnis
Contents 7 1.Introduction 11 Motivation 11 Outline 12 2.Theoretical Principles of Organic Electronic Materials and Devices 13 Organic Electronics 13 Organic Semiconductors 14 Charge Transport Mechanisms in Organic Semiconductors 16 Organic Field-effect Transistors 19 Operation 19 The Metal-Semiconductor Interface 22 The Dielectric 25 Film Morphology and Charge Transport in OFETs 27 Small Molecules 27 Semicrystalline Polymers 29 3.Solution Shearing and Control of Film Morphology 33 The Solution Shearing Method 34 Capillary Flow and the Pinned Contact Line. 36 Marangoni Flow 36 Shear Flow 37 Film Formation in Solution Shearing 38 Small Molecules 38 Polymers 43 Stick-and-slip Instabilities 50 Contact Angle Hysteresis and Stick-and-slip 52 Vibration-assisted Thin-film Solution Fabrication Methods 53 Effects on a Liquid stemming from Vibration 53 Relevant Characteristics 57 Vibrations and Thin-film Formation 58 Combining the Solution Shearing and Vibrations 61 4.Experimental Methods 63 Device Fabrication 63 Substrate Preparation 63 Electrode Evaporation . 65 Piezoshearing Setup 65 Thin-film Characterization 68 Cross-Polarized Optical Microscopy 68 Grazing Incidence Wide-Angle X-ray Scattering 71 Electrical characterization 77 Characterization 77 Mobility estimation and overestimation discussion 77 5.Alignment Improvement from Blending the Small molecule TIPS- pentacene with an inert Polymer 81 Introduction 81 Optimization of film morphology for TIPS-pentacene . 82 Device Fabrication 82 Electrical Characterization .. 83 Film morphology characterization 86 Fabrication of Ultra-low-voltage Operation Devices 96 Figure of Merit of this Study 97 6.Piezoshearing of Crystalline Materials 101 Introduction 101 Piezoshearing of Pristine TIPS-pentacene 102 Film Fabrication 102 Thin-film Characterization 102 TIPS-pentacene blended with PS in Toluene: Better Performing Devices 104 Piezoshearing of C8-BTBT 105 7.Addressing Stick-and-Slip Instabilities in solution-sheared films for Introduction 109 Device Fabrication 110 The Effect of Piezoshearing on Stick-and-Slip Instabilities 111 Increasing Shearing Speed 111 Thin-film Characterization 114 Electrical Characterization 116 Energy Barriers and Overcoming them with Vibration 119 Acceleration Threshold for Mitigating Stick-and-slip 122 8.Piezoshearing of Viscous Polymer Solutions 127 Introduction 127 Device Fabrication 128 DPP4DE-TT and Film Morphology 129 DPP6DO-TT, DPP6DO-T, and Faraday Instabilities 137 Thin-film Characterization 141 Piezoshearing as a Parametric Oscillator System 145 Solid Friction 146 Viscosity 146 Transition Between Regimes 147 9.Conclusion and Outlook 149 Conclusion 149 Outlook 150