Luận án tiến sĩ: Design and synthesis of organic semiconductors for use in organic field effect transistors

Design and Synthesis of Organic Semiconductors for use in Organic Field Effect Transistors By Amanda Ruth Murphy B. (Western Washington University) 2001 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the GRADUATE DIVISION of the UNIVERSITY of CALIFORNIA at BERKELEY Committee in charge: Professor Jean M. Fréchet, Chair Professor Peidong Yang Professor Vivek Subramanian Spring 2006 UMI Number: 3228434 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction.

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This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P. Box 1346 Ann Arbor, MI 48106-1346 Design and Synthesis of Organic Semiconductors for Use in Organic Field Effect Transistors Copyright © 2006 By Amanda Ruth Murphy Abstract Design and Synthesis of Organic Semiconductors for Use in Organic Field Effect Transistors By Amanda Ruth Murphy Doctor of Philosophy in Chemistry University of California, Berkeley Professor Jean M. Fréchet, Chair In the past ten years, much progress has been made in producing organic semiconductors with properties that rival amorphous silicon.

Organic semiconductors are sought for low-cost or large-area electronic devices such as organic field-effect transistors (OFETs), light-emitting diodes (OLEDs), photovoltaic cells, sensors, and radio frequency identification (RFID) tags. Low temperature processing options and the ductility of organic materials also allow flexible plastics or fabrics to be used as substrates. However, the majority of the newly developed materials are insoluble requiring the use of thermal evaporation to obtain thin films. In order for these organic semiconductors to compete as ‘low cost’ alternatives to silicon, manufacturers must be able to use large-area, continuous, reel-to-reel methods for production, which would likely involve the solution-based deposition methods such as spin coating, stamping, or printing.

Therefore, our work has focused on methods for solubilizing and controlling the self-assembly of conjugated oligomers in order to maximize the semiconducting properties from solution-based processes. Chapter 1 gives a general overview of charge transfer in organic semiconductors, and describes how devices are fabricated and tested. An extensive review of the literature on solution processed p- and n-type oligomers is also given. Chapter 2 and 3 discuss our initial attempts to produce soluble oligothiophenes capable of self-assembly.

Chapter 2 focuses on B-functionalized heptathiophene oligomers, while Chapter 3 deals with a-a’-substituted oligothiophene derivatives. The morphology, mechanical, and electrical properties of thermally evaporated, drop-cast and Langmuir-Blodgett (LB) monolayer and multilayer films on silicon dioxide and mica are studied in detail. A synthetic method for incorporating thermally removable solubilizing groups into organic semiconductors is outlined in Chapter 4, and demonstrated using a sexithiophene oligomer. The synthesis, chemical characterization, as well as an in-depth characterization of solution-processed films of this oligomer using AFM and NEXAFS spectroscopy is given.

This theme is carried over to Chapter 5, where a series of oligomers functionalized with these solubilizing groups were prepared in order to deduce various structure-property relationships. Organic field-effect transistors (OFETs) made from spun-cast films of these oligomers gave values are comparable with the best thermally evaporated thiophene oligomers reported in the literature, demonstrating the utility of our solubilizing method. In Chapter 6, we report the first OFET devices fabricated from self-assembled monolayers of end-functionalized thiophene oligomers. Oligomers containing organosilane and thiol binding groups were prepared and characterized.

Monolayer films were made using solution or Langmuir-Blodgett deposition techniques, and characterized by AFM, ellipsometry and NEXAFS spectroscopy. The performance and stability of these monolayers were investigated in bottom contact field-effect transistors. Finally, Chapter 7 discusses the synthetic strategy we have developed to access both regiorandom and regioregular polythiophenes containing electron-withdrawing carboxylate substituents. Although these polymers have extended conjugation lengths, they provide better oxidative doping stability than conventional polythiophenes due to the lowering of the HOMO energy levels by approximately 0.

High charge mobilities and on/off ratios are observed in OFETs fabricated entirely in air and remain stable over a period of months demonstrating the low propensity of these materials towards p- doping by molecular oxygen. Chair Date Table of Contents AcknowledgmeriS. ch HH KT KH Ki Ki SOLE KĐT iv Chapter 1: Introduction to Organic SemiconducfOrS. cuc nen nhe nén khe 1 0052.

eae enn EEE Anne aes 2 2. Conduction in Organic SemiconducforS.1 3D Structure and Charge Transport. cu nen nhe khe 4 2.2 Field Effect TransisfOFS. nn nn nh nh hờ 5 3.

Literature Review of Solution-Processed P-Type Oligomers. Literature Review of Solution-Processed N-Type Oligomers. EEG EEE SHES EEA ESHER EES23 Chapter 2: Synthesis of B-Functionalized Oligothiophenes and the Thin Film Morphology, Mechanical, and Electrical Propertfi@s. cuc nn nen nành he nhe 31 1.

cuc nh nH HH ng kế KT ĐC TK EERE EES 32 2. Results and DiscusSion. cuc non HH» by nh» nh hen KH tà tàn 32 2.1 Design and Synthesis.2 Evaporated and Solution Processed Film Morphology.3 Langmuir-Blodgett Monolayers of 'T7-COOH.4 OFET Device Construction and Performance. ng TH KH HH ch bà g3 kệ 49 4.

Materials and Methods. chen eee cent eae eeee eee es 50 5. nhàn bì ng nh nh eae 58 Chapter 3: Synthesis and AFM Studies of Carboxylic-Acid Functionalized Pentathio- phenes on Mica SuIÍaCc@S. LH nen nề nh» nh Đà kh rà 60 1.

In†fOdUCÍOP.- HH TH TT KH hà nà KT TT nh tà hy 61 2. Results and DiscUsSÌOn. cu HT nen nh bà ng nà Hà kh nh re 62 2. nen» nh nh nh nh tà62 2.2 Monolayer Film Formafion.

nh nén nh bà kén dao 64 2.3 Mechanical Properties of the Films.4 Dielectric and Electrical Dipole Properties of C10-5TBA Films. ác nành Hà HT HT HH KHE LH 80 4. Materials and Methods. cuc nn nhe nhe ĐH kh kết 81 5.

nhàn Hành HH HH KH KH HH ĐH C0 senses 89 Chapter 4: Film Morphology and Transistor Performance of Soluble Oligothiophene Derivatives Containing Thermally Removable Solubilizing Groups. HH HH HH TH KH KH kh ĐT ch BI 9 kg ha 93 2. Results and Discussion.-- HH HT ng vn nh khe 94 2.1 Oligomer Design and SyntheSis. che nhe nh nhe 94 2.3 Thin Film Morphology.4 Soft X-Ray Characterization of Thin Films.5 OFET Device Performance.

nen HH nhe 109 3.-- cá nén Hàn Hà HH HH KH Thi gi ĐH 114 4. Materials and Methods. con nh ng ng nhe 115 5. nành nhúnnà HH HH HH KH HH HH KH cà ền 128 Chapter 5: Molecular Ordering and Charge Mobility Trends In a Series of Solution- Processed Oligothiophene Ultrathin Films.

ch nh nàn Hà HH rà kế tà hi Là LHY 131 2. Results and Discussion.- ch nn «TH kh kh nhe 132 2.1 Oligomer Synthesis and Characterizafion.2 Thin Film Morphology. cc- nh nhe oe, 141 2.3 Molecular Orientation Evaluation by NEXAFS.4 Film Quality Analysis By NEXAFS. neers tetera ners 150 2.5 Film Morphology Discussion.

cu nhe nhe nhe Ha 152 2.6 OTFT Device Characterizafion.c nen nen nnn nhe hie 152 khe. Materials and Methods. ch nn kn kh nh nhà bến 156 "2. 182 Chapter 6: Self-Assembled Monolayer TransisfOFS.

nen nén nen hen 166 1. cu nh Hs HT» HT ĐK nh Ki EEE ch 167 2. Results and Discussion. cuc nen» nh nén he nhà ke 189 2.1 Oligomer Synth@SiS.- nen nh» Hs nh biet 169 2.2 Bulk Film Properties.3 Self-Assembled Monolayer Films.4 Langmuir-Blodgett Films.

Lee nh nh nh nh ve 177 3, Conclusions and Future Work. cece nh nh Hư bay 182 4. Materials and Methods.- nén nh nh KH ho bà rà 183 ban ¡ <=. 190 Chapter 7: Synthesis, Characterization, and Field-Effect Transistor Performance of Ester Functionalized Polythiophenes.

chen nh nh nh Ha 192 hoc n7 Add. Results and DiscUsSSiOn. ben» nhe Hàn He nà nha 194 2.1 Polymer Synthe@SiS. iu nen nen nh nh nề nh hà nen ens 194 2.-- Ác ĐH n HT Hà nhe Hà 203 2.

LG He HH ke nh nhe oa 205 KNe. Materials and Methods. cuc» nen nen ko hờn 210 ni ae. 216 Appendix A: Near-Edge X-ray Absorption Fine Structure Spectroscopy.-- LH HH rene eens esate Hs khi 220 A3.

HH HH TH KH KH HT kh Ki EU 224 11 Acknowledgements First, | would not be where | am today without several people who have encouraged me throughout my academic career. As far back as high school, Mr. Booth’s Advanced Chemistry/Physics class incited my love for science, and motivated me to pursue a science-oriented major in college. At Western, my advisor Steve Dillman was a constant source of encouragement throughout my five years in the engineering department.

My summer internship at IBM, working under the supervision of Robert Miller and Victor Lee, changed the course of my studies from engineering to chemistry. While at IBM, | was introduced to Professor Fréchet and without his help | would have never come to Berkeley. Professor Fréchet has been an outstanding mentor and an inspiration, and | am grateful that he gave me the chance to work in his laboratories. There are several people | have met here in Berkeley that have made the hardships of graduate school bearable and made my time here worthwhile.

My fellow classmates in the Fréchet group: Cameron Lee who tutored me through our first year of classes, Scott Baker for always having an inappropriate joke to make me laugh, and Stephany Standley. Cathy Liang and Brett Helms were the best lab-mates ever- they made me enjoy coming to work (even though Brett almost succeeded in setting me on fire!). The ‘Francis’ boys, especially Amish Patel, Neel Joshi, Jacob Hooker, and David Tilley, as well as Josh Goldberger were non-stop entertainment throughout the years. Lastly, | have to thank the ‘GNO’ club, Jen Prescher, Jenn Barbarow, Dorothea Fiedler and Stephany Standley, for many nights in the seedy clubs of SF! My family and friends back in Washington have also been a vital source of love and support.

My parents, Bill and Connie Murphy, are the most compassionate, generous, and devoted parents that anyone could ask for. My sister and brother, Michelle and Andre, have been great friends over the years, and | know they will always be there when | need them. 1V Lastly, my best girls, Suvantha Dickerson, Margen Carlson and Meghan Weston, have been an indispensable source of comfort and support, and are always good for a fantastic night out on the town! Finally- to my one and only John Matthew Antos- if for no other reason, | was meant to come to Berkeley to find you. | love you and | can’t wait to begin the next stage of our lives together in Boston.

Chapter 1 Introduction to Organic Semiconductors Abstract In the past ten years, there has been a flood of new research aimed at the development of organic semiconductors with properties that rival amorphous silicon. This chapter gives an overview of the basic charge transport mechanisms, device fabrication and electrical measurement, as well as a review of the literature on solution-processed oligomeric organic semiconductors. Introduction The solubility of organic semiconducting materials is a particularly important consideration when evaluating candidates for use in low cost electronic devices such as organic field-effect transistors (OFETs),'Š light-emitting diodes (OLEDs),** photovoltaic cells,"” 6-8 sensors,”"° and 11-13 radio frequency identification (RFID) tags, since the most economic processing methods for 3,14 15,16 these materials include solution-based methods such as spin coating," ˆ stamping, or ink-jet printing."”"® Suitably modified organic materials are compatible with solution processing techniques thereby eliminating the need for expensive lithography and vacuum deposition steps mandatory for most other solid-state materials such as silicon.