Synthesis of Cyanine Polyelectrolytes and Anions for Organic Electronic Devices THÈSE NO 7478 (2017) PRÉSENTÉE LE 9 FÉVRIER 2017 À LA FACULTÉ DES SCIENCES ET TECHNIQUES DE L'INGÉNIEUR UNITÉ DE RATTACHEMENT POUR SCIENTIFIQUES IMX PROGRAMME DOCTORAL EN CHIMIE ET GÉNIE CHIMIQUE ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE POUR L'OBTENTION DU GRADE DE DOCTEUR ÈS SCIENCES PAR Lei WANG acceptée sur proposition du jury: Prof. J.-E. Moser, président du jury Prof. F. Nüesch, Prof. C. R. Hinderling, directeurs de thèse Prof. E. Constable, rapporteur Dr F. Castro, rapporteur Prof. K. Sivula, rapporteur Suisse 2017 Zusammenfassung Zusammenfassung In den letzten Jahrzehnten wurden zahlreiche praktische Anwendungen von organischen elektronischen Bauelementen gezeigt. Aufgrund des Potenzials einer kostengünstigen Herstellung, ausgezeichneter Leistung und vielseitiger Funktionalitäten wie Flexibilität, Portabilität und Transparenz, werden sie als vielversprechende Alternativen zu anorganischen Halbleitertechnologien angesehen. In dieser Arbeit konzentrierte ich mich vor allem auf die Untersuchung einer speziellen Klasse organischer Halbleiter, Cyanin-Farbstoffen. Beginnend mit der Synthese von Cyaninpolyelektrolyten (Cy-Poly) und neuen Anionen wurden neue Funktionalitäten wie orthogonale Löslichkeit, Vernetzungsfähigkeit und Photosensibilisierungsfähigkeit eingeführt und die entsprechenden Materialien als aktive Komponenten in organischen elektronischen Bauelementen untersucht. Die Verwendung von Cyaninsalzen ermöglicht ein gemischtes ionisches/elektronisches Leitvermögen in festen organischen halbleitenden Dünnfilmen. Aufgrund der Anwesenheit von mobilen Anionen und ihrer Beförderung zu den jeweiligen Metallelektroden wird ein Ionenübergang erzeugt. Dies führt zu einer elektrochemischen Oxidation und Reduktion innerhalb des organischen Dünnfilms und zum Aufbau eines eingebauten elektrischen Feldes im intrinsischen Bereich mit Veränderung der potentiellen Energie. Die elektronische Leitfähigkeit wird in den dotierten Zonen erheblich verbessert, was die Ladungsinjektion an den Elektroden erleichtert. Der bemerkenswerte Potentialabfall im Übergangsbereich ermöglicht die Lichtemission der elektrolumineszenten Materialien sowie einen photovoltaischen Effekt bei der Beleuchtung mit weißem Licht. Ein besonderes Interesse galt der Stabilisierung ionischer Verbindungen in organischen elektronischen Bauelementen aus Cyanin-Farbstoffen, durch chemische Fixierung der ionischen Träger in der gewünschten Position. In den Bauteilen, welche die immobilisierbaren Phenylazid-Anionen enthalten, wurde ein unerwartetes Exiton-Quenching- Verhalten beobachtet, das der Triplett Sensibilisierung von Trimethincyaninen auf die Photodekomposition von 4-Azidobenzoat-Ionen zugeschrieben wurde. Stichwörter: organische Photovoltaik, lichtemittierende elektrochemische Zelle, Photoleitfähigkeit, Triplett Photosensibilisator, Cyanin-Farbstoff, Phenylazid i Abstract Abstract Many practical applications among organic electronic devices have been demonstrated over the last decades. They are considered as promising alternatives to inorganic semiconductor technologies due to the potential of cost-effective fabrication, excellent performance and versatile functionalities such as flexibility, portability and transparency. In this work, I mainly focused on the investigation of a special class of organic semiconductors, cyanine dyes. Starting with the synthesis of cyanine polyelectrolytes (Cy-Poly) and novel anions, new functionalities such as orthogonal solubility, crosslinking capability and photosensitizing ability were introduced and the corresponding materials as active components in organic electronic devices were explored. The utilization of cyanines allows for the mixed ionic/electronic conduction in solid organic semiconducting thin films. Due to the presence of mobile anions, an ionic junction is created as a result of the ionic motion towards respective metal electrodes. This leads to electrochemical oxidation and reduction within the organic thin film and the establishment of a built-in electric field across the intrinsic region with potential energy shifts. The electronic conductivity is considerably enhanced in the doped zones, which facilitates charge injection from the electrodes. The remarkable potential drop in the intrinsic region enables light emission of the electroluminescent materials as well as a photovoltaic response upon white light illumination. A special interest was given to the stabilization of ionic junctions in cyanine dye organic electronic devices by chemically fixing the ionic carriers in the desired position. Unexpected exciton quenching behavior was observed in the devices containing the immobilizable phenyl azide anions, which was attributed to the triplet sensitization effect of trimethine cyanines on the photodecomposition of 4-azido benzoate ions. Keywords: organic photovoltaics, light-emitting electrochemical cells, photoconductivity, triplet photosensitizer, cyanine dye, phenyl azides ii Acknowledgements Acknowledgements I had a great honor to spend four years, which took one seventh of my life up to now, to pursue a PhD degree in this fantastic country Switzerland. (Un)fortunately this is going to come to an end. Before saying goodbye to everything here, I take this excellent opportunity to acknowledge all the people that have been involved in my life within this period. To start with, I would like to acknowledge my supervisor, Prof. Frank Nüesch, for accepting me as his PhD student, which initiated the whole story. He is always very kind and nice, and with a bit sense of humor. He regularly gives important scientific inputs during the group meetings and tries to offer key advice on my PhD project. Although he is quite busy, he is able to balance his efforts and offer opportunities to each student. It is a great pleasure for me to accomplish my study under his supervision. I would like to extend my deep gratitude to my co-supervisor, Prof. Christian Hinderling. He looks very energetic all the time and always smiles to everybody. He provides me with a spacious laboratory and a nice office, and he contributes to my PhD project significantly with precious ideas and fruitful discussions. Also, many thanks are given to him again for offering me the opportunities to undertake responsibilities for AFM and some scientific tasks in addition to the PhD project. Furthermore, I am very grateful to my group leader, Dr. Roland Hany. He is very patient and has an easy-going personal character. He predominantly guides my project with his solid knowledge and rich experience and constantly modifies the direction of my work with brilliant ideas to achieve our mutual goals. I would also like to thank my mentor, Prof. Kevin Sivula, for several helpful scientific discussions and nice conversations in his office or during the workshops in the Swiss mountains. Special thanks go to Prof. Andreas Lendlein (HZG, Germany), Prof. Manfred Wagner (TU Berlin, Germany) and Prof. Jin Xu (Xiamen University, China) for generously offering me recommendation letters, which were crucial for the successful enrollment at EPFL. I heartfelt thank all my colleagues at Empa and ZHAW who helped me with their time and expertise, which considerably contributed to the success of my work. Particularly Dr. Jakob Heier for fluorescence, profilometry and AFM measurements, Dr. Hui Zhang for initially iii Acknowledgements teaching me the fabrication and characterization of devices, Sandra Jenatsch for sharing the same SNF project and exploring the potential application of my dyes, Dr. Daniel Rentsch for NMR measurements, Dr. Mohammed Makha for lamination experiments and frequently transporting nitrogen tanks together with vital information exchange, Claudia Konrad and Fabian Deuber for their numerous little helps at the initial stage of my PhD, Beatrice Fischer for TGA, DSC, IR and GPC measurements, Dr. Peter Lienemann, Samuel Menzi and Jasmin Keist for XRF measurements, Dr. Sebastian Opitz for ESI-MS measurements, Dr. Dalin Wu, Dr. Manolis Tzirakis and Yongzen Tan for various chats about work, career and life during lunches and coffee breaks, Thibaud Fleurieau-Lintz for being the other chemist working with PFB anions besides me, Yeesong Ko, Simon Dünki, Anna Véron, Jean-Nicolas Tisserant, Jose Enrico Quinsaat, Chuyao Peng, Nicolas Leclaire, Donatas Gesevicius, Surendra Babu Anantharaman, Philip Caspari, Roland Steim and Anand Verma for many good moments together during everyday work and group events. I also thank the numerous friends that I have met and worked with in ACSSZ and that I have played with during badminton, skiing and swimming. All these people and activities significantly enriched my experience, brought much joy to me and made my life in Switzerland truly colorful. Last but not least, I must thank my wife, Yuting Zhang, for accompanying me in a foreign country. She understands me and believes in me. She spares no effort to take care of our little daughter, Ziyan Wang, without bothering me as far as possible. However, I feel quite sorry for them since I am very often not able to be with them during the evenings or over the weekends. Moreover, I feel shame that the first illness of my daughter in her life was because of me. So, be stronger, overcome various difficulties, WEILAIWOMENHUINIUBIDEBUDELIAO (translation: we have a bright future). Yes, the end is here. Lei Wang Oct. 2016 in Dübendorf iv Table of Contents Table of Contents Zusammenfassung ....................................................................................................................................................