University of Groningen
Structure-property and film formation mechanism in PEDOT:PSS based and perovskites systems
Dong, Jingjin
DOI:
10.33612/diss.166892884
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Publication date: 2021
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Dong, J. (2021). Structure-property and film formation mechanism in PEDOT:PSS based and perovskites systems. University of Groningen. https://doi.org/10.33612/diss.166892884
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Summary
With the global population continuously growing and industrialization on the rise in different developing countries, the energy requirement has increased to unprecedented levels. Thus there is a crucial need for clean energy sources, alternative to fossil fuel, to satisfy this massive energy need without continue harming the environment. Among the different clean energy sources, solar energy and energy generated by thermoelectric materials are two promising solutions. In both cases, the future use of these clean energy solutions relies on the stability and efficiency of the active materials composing the devices. As the efficiency of the devices is dictated in large part by the nanostructure of the active materials, fundamental studies are required to optimize the material structure at the nanoscale.
Poly(3,4-ethylenedioxy thiophene):poly(styrenesulfonate) (PEDOT:PSS) is a conducting polymer that holds great characteristics such as chemical stability, green-processing, flexibility, high electrical conductivity and ease of modulation of its conducting properties. These properties make PEDOT:PSS one of the most promising p-type organic conducting materials for flexible electronic and thermoelectric (TE) applications. After a brief introduction about conducting polymers and PEDOT:PSS, various strategies able to tune the structure and thus the properties of PEDOT:PSS are reviewed in Chapter 1. These strategies involve the use of polar solvents, acid-base solutions and the introduction of nanoparticles. In addition, a brief introduction on the critical role of synchrotron light, specifically in situ grazing incidence wide angle X-ray scattering (GIWAXS), in the field of organic thermoelectrics, organic photovoltaics and also perovskite materials is presented.
Despite the large amount of literature on PEDOT:PSS, detailed knowledge of the mechanisms involved in the structural rearrangements occurring at the nanoscale and induced by the different treatment agents is usually ignored, even for the most widely used methods such as polar solvent or acid-base treatment.
To fill this gap, a systematic and quantitative study of the effect of solvent polarity and solution processing on the film structure and conductivity of PEDOT:PSS is presented in
Chapter 2. By using GIWAXS together with atomic force microscopy (AFM), we highlight
the importance of the quality of the PEDOT crystal packing rather than the overall degree of crystallinity as a key factor to reach improved electrical conductivity. Moreover, the (re)structuring mechanisms occurring during the film formation and during post-treatment agent exposure is elucidated by in situ GIWAXS. Different intermediate precursor stages and different pathways to reach improved crystallinity are reported depending on the used solvents. The structural results are interpreted looking at the solvent nature and the PSS/solvent affinity.
The effect of base solution treatment is studied in Chapter 3. A comparative study on the post-treatment effect using three common and green alkali base solutions, namely LiOH, NaOH and KOH, is presented. The structural modification induced in the film by the base post-treatment are studied by techniques such as AFM, GIWAXS, UV-vis-NIR and
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attenuated total reflectance-Fourier-transform infrared (ATR-FTIR). A correlation between the thermoelectric properties and the mechanism of base solution post-treatment is revealed. The results presented in this part of the work shed light on the structural reorganization occurring in PEDOT:PSS when exposed to high pH solutions and are explained on the basis of the alkali cations’ different affinity to PSS-, putting emphasis on the effect of different ions.
The counter-intuitive conclusions drawn from this chapter and Chapter 2 deliver an idea that the usage of novel characterization techniques such as in situ GIWAXS can play a critical role in revealing mechanisms that have been widely ignored.
While the first two experimental chapters focus on the deep understanding of solution-based strategies, Chapter 4 presents a new approach to improve the TE properties of PEDOT:PSS based films. Blending with other inorganic counterparts is considered as a good strategy to further improve the PEDOT:PSS TE properties, however only few attempts have been successful so far, due to difficulty in creating an ideal contact between the organic and inorganic components or due to the difficulty in efficiently disperse the inorganic materials inside the polymer matrix. Here we include naked tin oxide nanoparticles (SnOx-NPs) inside PEDOT:PSS. The nanoparticles are generated by means of spark discharge generation and they are incorporated into the polymeric thin films using a low-energy deposition mode (diffusion mode). GIWAXS and X-ray photoelectron spectroscopy (XPS) suggest great interactions occurring in the topper most film layer between PSS and SnOx-NPs. The subsequent structural reorganization induces an improvement in the PEDOT chain packing and thus faster carrier mobility, so that the system electrical conductivity is practically retained. However, the phase boundaries introduced by Sn-NPs lead to dramatically enhancement of the Seebeck coefficient. In this way, an optimized power factor of about 116 μWm-1K-2 is obtained, among the highest reported for organic-inorganic hybrid systems. The
mechanism revealed may inspire future research in the TE and flexible electronic fields. This deposition strategy holds great potential in industrialized large-scale production of flexible TE devices. Comparing to all the other proven methods that have been reported, this one may be the easiest, avoiding any chemical synthesis, post-treatment or washing steps. Besides, the non-toxic tin electrode used makes it environmentally friendly.
In Chapter 5 we devoted our attention to the structure-property study in another important class of energy-related materials such as perovskite materials for photovoltaic applications. Here, the in situ GIWAXS approach is used to discover the mechanism of formation, orientation and location of phases inside thin perovskite films, which is essential to optimize their optoelectronic properties. Among the most promising, low toxicity, lead-free perovskites, the tin-based ones are receiving much attention but are not extensively studied as the lead ones. The chapter reports an extensive in situ and ex situ structural study allowing to understand the mechanism of crystallization from solution of 3D formamidinium tin iodide (FASnI3), 2D phenylethylammonium tin iodide (PEA2SnI4) and hybrid PEA2FAn-1SnnI3n+1
Ruddlesden-Popper (RDP) perovskites. Addition of small amounts of low-dimensional component promotes oriented 3D-like crystallite growth in the top part of the film, together with an aligned quasi-2D bottom-rich phase. While sporadic nucleation rapidly occurs in the bulk of the drying film concomitantly to surface crystallization in the pure 3D system, bulk
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nucleation is negligible in the pure 2D and in the hybrid RDP systems with sufficiently high PEA content. Moreover, tin-based perovskites form through direct conversion of a disordered precursor phase without forming ordered solvated intermediates and thus without the need of thermal annealing steps. Our findings shed light onto the mechanism of formation of one of the most promising Sn-based perovskites and will provide fundamental information on how to further improve the performances of these interesting lead-free materials.
In summary, this thesis aims to reveal the structure-property relationship of two materials promising for energy applications: PEDOT:PSS based organic films and lead-free perovskites. The results contained in this thesis highlight the importance of structural studies at the nanoscale and often in situ during processing to explain the alteration of the electrical and photovoltaic properties of the materials. In particular, it becomes clear that playing with the interactions and solubility between the different components of the active materials and the added components (organic solvents, acids, bases or even external nanoparticles) is a powerful tool to optimize the performances of renewable clean energy devices.
Samenvatting
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Samenvatting
Door de voortdurende groei van de wereldbevolking en de toenemende industrialisatie in verschillende ontwikkelingslanden is de energiebehoefte tot ongekende hoogten gestegen. Er is dus een cruciale behoefte aan schone energiebronnen, als alternatief voor fossiele brandstoffen, om aan deze enorme energiebehoefte te voldoen zonder het milieu verder schade te berokkenen. Van de verschillende schone energiebronnen zijn zonne-energie en energie opgewekt door thermo-elektrische materialen twee veelbelovende oplossingen. In beide gevallen is het toekomstige gebruik van deze schone energieoplossingen afhankelijk van de stabiliteit en de efficiëntie van de actieve materialen waaruit de apparaten zijn opgebouwd. Aangezien de efficiëntie van de apparaten voor een groot deel wordt bepaald door de nanostructuur van de actieve materialen, zijn fundamentele studies nodig om de materiaalstructuur op nanoschaal te optimaliseren.
Poly(3,4-ethyleendioxythiofeen):poly(styrenesulfonaat) (PEDOT:PSS) is een geleidend polymeer met grote eigenschappen zoals chemische stabiliteit, groene verwerking, flexibiliteit, hoog elektrisch geleidingsvermogen en gemakkelijke modulatie van zijn geleidende eigenschappen. Deze eigenschappen maken PEDOT:PSS tot één van de meest veelbelovende p-type organische geleidende materialen voor flexibele elektronische en thermo-elektrische (TE) toepassingen. Na een korte inleiding over geleidende polymeren en PEDOT:PSS, worden in Hoofdstuk 1 verschillende strategieën besproken om de structuur en dus de eigenschappen van PEDOT:PSS aan te passen. Deze strategieën omvatten het gebruik van polaire oplosmiddelen, zuur-base oplossingen en de introductie van nanodeeltjes. Daarnaast wordt een korte inleiding gegeven over de cruciale rol van synchrotronlicht, met name in situ grazing incidence wide angle X-ray scattering (GIWAXS), op het gebied van organische thermo-elektrische materialen, organische fotovoltaïsche materialen en ook perovskietmaterialen.
Ondanks de grote hoeveelheid literatuur over PEDOT:PSS is gedetailleerde kennis van de mechanismen die betrokken zijn bij de structurele herschikkingen op nanoschaal en geïnduceerd door de verschillende behandelingsmiddelen meestal onbestaande, zelfs voor de meest gebruikte methoden zoals behandeling met polaire oplosmiddelen of zuur-base. Om deze leemte op te vullen wordt in Hoofdstuk 2 een systematische en kwantitatieve studie gepresenteerd van het effect van de polariteit van het oplosmiddel en de behandeling van de oplossing op de filmstructuur en geleidbaarheid van PEDOT:PSS. Door gebruik te maken van GIWAXS in combinatie met atoomkrachtmicroscopie (AFM), benadrukken we het belang van de kwaliteit van de PEDOT-kristalpakkingen in plaats van de totale kristalliniteitsgraad als sleutelfactor om een verbeterde elektrische geleiding te bereiken. Bovendien worden de (her)structureringsmechanismen die optreden tijdens de filmvorming en tijdens de blootstelling aan nabehandelingsagentia opgehelderd door in situ GIWAXS. Verschillende tussenstadia van precursoren en verschillende routes om een verbeterde kristalliniteit te bereiken worden gerapporteerd, afhankelijk van de gebruikte solventen. De structurele resultaten worden geïnterpreteerd aan de hand van de aard van het oplosmiddel
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en de affiniteit tussen PSS en oplosmiddel.
Het effect van de behandeling van de basisoplossing wordt bestudeerd in Hoofdstuk 3. Er wordt een vergelijkende studie gepresenteerd van het effect van de nabehandeling met drie gangbare en groene alkali baseoplossingen, namelijk LiOH, NaOH en KOH. De structurele veranderingen in de film door de nabehandeling met base worden bestudeerd met technieken zoals AFM, GIWAXS, UV-vis-NIR en verzwakt totaal reflectie-Fourier-transform infrarood (ATR-FTIR). Een correlatie tussen de thermo-elektrische eigenschappen en het mechanisme van de nabehandeling van de basisoplossing wordt onthuld. De in dit deel van het werk gepresenteerde resultaten werpen licht op de structurele reorganisatie die optreedt in PEDOT:PSS bij blootstelling aan oplossingen met een hoge pH-waarde en worden verklaard op basis van de verschillende affiniteit van de alkali-kationen voor PSS-, waarbij de nadruk wordt gelegd op het effect van verschillende ionen. De contra-intuïtieve conclusies uit dit hoofdstuk en Hoofdstuk 2 geven aan dat het gebruik van nieuwe karakteriseringstechnieken zoals in situ GIWAXS een cruciale rol kan spelen bij het blootleggen van mechanismen die op grote schaal werden genegeerd.
Terwijl de eerste twee experimentele hoofdstukken zich richten op het diepgaand begrip van oplossingsgerichte strategieën, presenteert Hoofdstuk 4 een nieuwe benadering om de TE-eigenschappen van op PEDOT:PSS gebaseerde films te verbeteren. Het mengen met andere anorganische tegenhangers wordt beschouwd als een goede strategie om de TE-eigenschappen van PEDOT:PSS verder te verbeteren, maar tot nu toe zijn slechts enkele pogingen succesvol geweest, vanwege de moeilijkheid om een ideaal contact te creëren tussen de organische en anorganische componenten of vanwege de moeilijkheid om de anorganische materialen efficiënt te dispergeren binnen de polymeermatrix. Hier nemen we naakte tinoxide nanodeeltjes (SnOx-NPs) op in PEDOT:PSS. De nanodeeltjes worden gegenereerd door middel van vonkontlading en ze worden opgenomen in de polymere dunne films met behulp van een lage-energie depositie mode (diffusie-modus). GIWAXS en X-straal foto-elektron spectroscopie (XPS) suggereren dat er grote interacties optreden in de bovenste laag van de film tussen PSS en SnOx-NPs. De daaropvolgende structurele reorganisatie leidt tot een verbetering van de PEDOT-ketenpakking en dus tot een snellere dragermobiliteit, zodat het elektrische geleidingsvermogen van het systeem praktisch behouden blijft. De door de Sn-NP's geïntroduceerde fasegrenzen leiden echter tot een sterke verhoging van de Seebeck-coëfficiënt. Op die manier wordt een geoptimaliseerde vermogensfactor van ongeveer 116 μWm-1K-2 verkregen, één van de hoogste die voor organisch-anorganische hybride systemen werden gerapporteerd. Het onthulde mechanisme kan een inspiratiebron zijn voor toekomstig onderzoek op het gebied van TE en flexibele elektronica. Deze afzettingsstrategie biedt grote mogelijkheden voor de geïndustrialiseerde grootschalige productie van flexibele TE-apparaten. In vergelijking met alle andere bewezen methodes die zijn gerapporteerd, is deze misschien wel de gemakkelijkste, omdat er geen chemische synthese, nabehandeling of wasstappen nodig zijn. Bovendien maakt de gebruikte niet-toxische tinelektrode deze methode milieuvriendelijk.
In Hoofdstuk 5 hebben we onze aandacht gewijd aan de structuur-eigenschap studie in een andere belangrijke klasse van energie-gerelateerde materialen, zoals perovskiet materialen or
Samenvatting
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fotovoltaïsche toepassingen. Hier wordt de in situ GIWAXS benadering gebruikt om het mechanisme van vorming, oriëntatie en locatie van fasen binnen dunne perovskiet films te ontdekken, wat essentieel is om hun opto-elektronische eigenschappen te optimaliseren. Onder de meest veelbelovende, loodvrije perovskieten met lage toxiciteit, krijgen de tin-gebaseerde perovskieten veel aandacht, maar ze zijn niet zo uitgebreid bestudeerd als de lood-gebaseerde perovskieten. Dit hoofdstuk rapporteert een uitgebreide in situ en ex situ structuurstudie die het mogelijk maakt om het mechanisme van kristallisatie vanuit oplossing van 3D formamidinium tinjodide (FASnI3), 2D fenylethylammonium tinjodide (PEA2SnI4)
en hybride PEA2FAn-1SnnI3n+1 Ruddlesden-Popper (RDP) perovskieten te begrijpen.
Toevoeging van kleine hoeveelheden laagdimensionale component bevordert georiënteerde 3D-achtige kristallietgroei in het bovenste deel van de film, samen met een uitgelijnde quasi-2D bodem-rijke fase. Terwijl sporadische nucleatie snel optreedt in de bulk van de drogende film gelijktijdig met oppervlakte kristallisatie in het pure 3D systeem, is bulk nucleatie verwaarloosbaar in de pure 2D en in de hybride RDP systemen met voldoende hoog PEA gehalte. Bovendien vormen tin-gebaseerde perovskieten zich door directe conversie van een ongeordende precursorfase zonder de vorming van geordende opgeloste tussenproducten en dus zonder de noodzaak van thermische gloeistappen. Onze bevindingen werpen licht op het vormingsmechanisme van een van de meest veelbelovende Sn-gebaseerde perovskieten en zullen fundamentele informatie opleveren over hoe de prestaties van deze interessante loodvrije materialen verder kunnen worden verbeterd.
Samenvattend beoogt dit proefschrift de structuur-eigenschapsrelatie te onthullen van twee materialen die veelbelovend zijn voor energietoepassingen: PEDOT:PSS gebaseerde organische films en loodvrije perovskieten. De resultaten in dit proefschrift benadrukken het belang van structuurstudies op nanoschaal en vaak in situ tijdens de verwerking om de verandering van de elektrische en fotovoltaïsche eigenschappen van de materialen te verklaren. In het bijzonder wordt duidelijk dat het spelen met de interacties en oplosbaarheid tussen de verschillende componenten van de actieve materialen en de toegevoegde componenten (organische oplosmiddelen, zuren, basen of zelfs externe nanodeeltjes) een krachtig hulpmiddel is om de prestaties van hernieuwbare schone-energieapparaten te optimaliseren.
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Publications
As the first author:
1. J. Dong#, S. Shao#, S. Kahmann, A. J. Rommens, D. Hermida-Merino, G. H. ten Brink, M. A. Loi, G. Portale, Mechanism of Crystal Formation in Ruddlesden-Popper Sn-Based Perovskites. Advanced Functional Materials, 2001294 (2020).
2. J. Dong, G. Portale, Role of the Processing Solvent on the Electrical Conductivity of PEDOT:PSS. Advanced Materials Interfaces, 2000641 (2020).
3. C. Ma#, J. Dong#, M. Viviani#, I. Tulini, N. Pontillo, S. Maity, Y. Zhou, W. H. Roos, K. Liu, A. Herrmann, G. Portale, De Novo Rational Design of A Freestanding, Supercharged Polypeptide, Proton-Conducting Membrane. Science Advances, 6, eabc0810 (2020).
4. J. Dong, Jian Liu, Xinkai Qiu, Ryan Chiechi, L. Jan Anton Koster, Giuseppe Portale. Engineering the Thermoelectrical Properties of PEDOT:PSS by Alkali Metal Ion Effect.
Engineering, accepted (2021).
5. J. Dong, Dominic Gerlach, Panagiotis Koutsogiannis, Petra Rudolf, Giuseppe Portale. Boosting the thermoelectric properties of PEDOT:PSS via low-impact deposition of tin oxide nanoparticles. Advanced Electronic Materials, accepted (2021).
As a co-author:
1. G. Fleury, D. Hermida-Merino, J. Dong, K. Aissou, A. Bytchkov, G. Portale, Micellar-Mediated Block Copolymer Ordering Dynamics Revealed by In Situ Grazing Incidence Small-Angle X-Ray Scattering during Spin Coating. Adv. Funct. Mater. 29, 1806741 (2019). 2. J. Liu, Y. Shi, J. Dong, M. I. Nugraha, X. Qiu, M. Su, R. C. Chiechi, D. Baran, G. Portale, X. Guo, L. J. A. Koster, Overcoming Coulomb Interaction Improves Free-Charge Generation and Thermoelectric Properties for n-Doped Conjugated Polymers. ACS Energy Lett. 4, 1556– 1564 (2019).
3. J. Liu, L. Qiu, R. Alessandri, X. Qiu, G. Portale, J. Dong, W. Talsma, G. Ye, A. A. Sengrian, P. C. T. Souza, M. A. Loi, R. C. Chiechi, S. J. Marrink, J. C. Hummelen, L. J. A. Koster, Enhancing Molecular n-Type Doping of Donor-Acceptor Copolymers by Tailoring Side Chains. Adv. Mater. 30, 1704630 (2018).
4. S. Shao, J. Dong, H. Duim, G. H. ten Brink, G. R. Blake, G. Portale, M. A. Loi, Enhancing the Crystallinity and Perfecting the Orientation of Formamidinium Tin Iodide for Highly Efficient Sn-Based Perovskite Solar Cells. Nano Energy. 60, 810–816 (2019). 5. J. Liu, B. van der Zee, R. Alessandri, S. Sami, J. Dong, M. I. Nugraha, A. J. Barker, S. Rousseva, L. Qiu, X. Qiu, N. Klasen, R. C. Chiechi, D. Baran, M. Caironi, T. D. Anthopoulos, G. Portale, R. W. A. Havenith, S. J. Marrink, J. C. Hummelen, L. J. A. Koster, N-type Organic Thermoelectrics: Demonstration of ZT > 0.3. Nat. Commun. 11, 5694 (2020).
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6. X. Qiu, V. Ivasyshyn, L. Qiu, M. Enache, J. Dong, S. Rousseva, G. Portale, M. Stöhr, J. C. Hummelen, R. C. Chiechi, Thiol-Free Self-Assembled Oligoethylene Glycols Enable Robust Air-Stable Molecular Electronics. Nat. Mater. 19, 330–337 (2020).
7. S. Shao, Y. Cui, H. Duim, X. Qiu, J. Dong, G. H. ten Brink, G. Portale, R. C. Chiechi, S. Zhang, J. Hou, M. A. Loi, Enhancing the Performance of the Half Tin and Half Lead Perovskite Solar Cells by Suppression of the Bulk and Interfacial Charge Recombination.
Adv. Mater. 30, 1803703 (2018).
8. N. Y. Doumon, F. V. Houard, J. Dong, P. Christodoulis, M. V. Dryzhov, G. Portale, L. J. A. Koster, Improved photostability in ternary blend organic solar cells: The role of [70]PCBM. J. Mater. Chem. C. 7, 5104–5111 (2019).
9. N. Y. Doumon, F. V. Houard, J. Dong, H. Yao, G. Portale, J. Hou, L. J. A. Koster, Energy level modulation of ITIC derivatives: Effects on the photodegradation of conventional and inverted organic solar cells. Org. Electron. 69, 255–262 (2019).
10. D. J. Mulder, L. M. W. Scheres, J. Dong, G. Portale, D. J. Broer, A. P. H. J. Schenning, Fabrication and Postmodification of Nanoporous Liquid Crystalline Networks via Dynamic Covalent Chemistry. Chem. Mater. 29, 6601–6605 (2017).
11. M. Golkaram, L. Boetje, J. Dong, L. E. A. Suarez, C. Fodor, D. Maniar, E. Van Ruymbeke, S. Faraji, G. Portale, K. Loos, Supramolecular Mimic for Bottlebrush Polymers in Bulk. ACS Omega. 4, 16481–16492 (2019).
12. M. Abdu‐Aguye, N. Y. Doumon, I. Terzic, J. Dong, G. Portale, K. Loos, L. J. A. Koster, M. A. Loi, Can Ferroelectricity Improve Organic Solar Cells? Macromol. Rapid Commun. 41, 2000124 (2020).
13. Q. Wang, S. Shao, B. Xu, H. Duim, J. Dong, S. Adjokatse, G. Portale, J. Hou, M. Saba, M. A. Loi, Impact of the Hole Transport Layer on the Charge Extraction of Ruddlesden-Popper Perovskite Solar Cells. ACS Appl. Mater. Interfaces. 12, 29505–29512 (2020). 14. S. Shao, W. Talsma, M. Pitaro, J. Dong, S. Kahmann, A. J. Rommens, G. Portale, M. A. Loi, Field‐Effect Transistors Based on Formamidinium Tin Triiodide Perovskite. Adv.
Funct. Mater. 31, 2008478 (2021).
15. J. Liu, G. Ye, H. G. O. Potgieser, M. Koopmans, S. Sami, M. I. Nugraha, D. R. Villalva, H. Sun, J. Dong, X. Yang, X. Qiu, C. Yao, G. Portale, S. Fabiano, T. D. Anthopoulos, D. Baran, R. W. A. Havenith, R. C. Chiechi, L. J. A. Koster, Amphipathic Side Chain of a Conjugated Polymer Optimizes Dopant Location toward Efficient N‐Type Organic Thermoelectrics. Adv. Mater. 33, 2006694 (2021).
16. M. Koopmans, M. A. T. Leiviskä, J. Liu, J. Dong, L. Qiu, J. C. Hummelen, G. Portale, M. C. Heiber, L. J. A. Koster, Electrical Conductivity of Doped Organic Semiconductors Limited by Carrier-Carrier Interactions. ACS Appl. Mater. Interfaces. 12, 56222–56230 (2020)
Acknowledgement
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Acknowledgement
Dear friends and readers, finally we are at this page. Before the special feelings fill my heart, it is a perfect moment now to express my gratitude to people who support my research and make my life happier during the past four years. Without your continued support and encouragement, it would be impossible to finish my PhD.
First and foremost, my sincerest and deepest appreciation goes to my supervisor Prof. Giuseppe Portale. Dear Giuseppe, I have said so many thanks to you during my PhD because you kept sorting me out. It was not too long since the start of my PhD when I realize how precious to have a supervisor who is always available and open for discussion. You are always full of energy and full of great ideas. Every one more talk we had makes me more confident because you always gave me positive and creative feedbacks. Your passion on the scientific research will always encourage me in my career. You have shown me how a scientist should work and what amazing output we can achieve if we work hard and smart. You guide me not only by in-depth academic knowledge, but more importantly by the power of critical reasoning, which is the greatest achievement during my research. Yes, you are a great leader. I believe the temperament of a group is most determined by its leader and you are such a tough and interesting guy that makes our Polymer Physics group a really cool team. I’m proud of being a member in it and I will never forget the time in our lab, in the synchrotron facilities and in the conferences. You have also shown me how to be a good husband and good father. I’m not sure if I can have a work-life balance like you, but I will try my best. In a word, it is so lucky to be a PhD candidate in your group. I hope you and your family stay healthy and happy all the time.
Next, I would like to thank my promotor Prof. Katja Loos. Dear Katja, thank you for being my promotor and holding me in the Polymer Chemistry group. Your sincere attitude towards scientific research and devotion to the work will always inspires me.
I would like to thank the assessment committee Prof. René Janssen, Prof. Georges Hadziioannou, and Prof. Moniek Tromp for proofreading the thesis and valuable comments. Prof. Maria A. Loi, thank you for the discussion and precious suggestions. Your contribution in Chapter 5 is very important to me. Besides, I would also thank you for being willing to be the reference contact for me. Prof. Jan Anton Koster, thank you too.
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department who gave such a lot of professional training and helps during my project. A distinctive acknowledge is owed to Jin who introduced me to Giuseppe’s group, and above that for your helpful, constructive discussion during our meetings. Also, I would like to express my gratitude to Ivan, Dina, Masyitha, Anton, Antonis, Milad and all the other group members for all kinds of help in the lab and discussions in the group meetings which were always inspiring to me. Ivan, thanks for being a helpful ‘neighbor’, especially when I was fresh in Groningen. Chongnan, Qi, Xiaohong and Tonghua, thanks for your support and help in the past years. I enjoyed the daily talk and the scientific discussions we had.
Special thanks goes to our Polymer Physics group members. Marco, you are one of the most hard working people I’ve met. I’m happy to work with you in the past four years. I’m sure you will have great success in the future career. Federico, my mate, thanks for the support, especially the help in ESRF. I wish you all the best during your PhD journey. Apostolos, we had a great time in this lovely group and you were definitely an important part for the great environment. You are always willing to help, and sometimes it is even too much. But I really appreciate your contribution. Gabor, Gianni, and Eleonora, we didn’t spend too much time together due to the Covid-19. You are so talented fresh blood and I’m very happy to have you in the group.
Karin, thanks for the paper work you did for me. All these conference registrations, form filling, and financial reimbursement make my research life easier. Jur, Albert and Peter, thanks for your technical support in the lab. It is very nice to have you in the group.
I am also deeply obliged to Dr. Jian Liu for the technical support in thermoelectric measurement and the professional suggestions. You are so productive and creative and I have learnt a lot from you. It is a great experience to collaborate with you. The same gratitude goes to Dr. Shuyan Shao. I wish you all the best for your future career.
Dear Dr. Dominic Gerlach and Prof. Petra Rudolf, thanks for the great measurement and analysis of XPS. Without your excellent contribution it is impossible to have the work presented in Chapter 4. I wish you and your family stay healthy and happy all the time. Dr. Gang Ye and Dr. Xinkai Qiu, thanks for providing the synthesized materials. Your contributes means a lot to me. Dr. Yanxi Zhang, thank you for the metal deposition training. The talk with you is always inspiring.
Xuwen, thanks for helping measuring the UV spectra. We come from the same institute in Suchow, and if not the pandemic, we could have had a drink together.
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lot.
Heng, thank you for being a great collaborator. I’m sure our work has its value and will be published in a good journal.
My USTC friends, Jin, Qihong, Xu, Yanxi, Chengyong and of course Yingfen, it is so lucky to meet you in Groningen. We had so much great time together, we drank, we sung and we played games. I hope we will meet each other in China mainland in the future.
The lovely friends from BME group, Linyan, Huaiying, Damla, Yong and Yuanfeng, Qihui and Yingruo, Valentina, JP, Hongping, Zhiwei, Bingran and Feifei, Kecheng, Ruifang, Linzhu, thank you for all the support.
Bingran, thank you for the Corona virus test and the drive to the airport. Linyan, thank you for helping holding Rapper when we came back to China.
Qihui, JP, thank you for arranging so many great parties.
Lu and Xueping, thank you for being wonderful neighbors since 2020. It is really special experience to quarantine inside the house when the weather is so good in Netherlands, but it is easier to have you during the Corona time.
Lei, thank you for the wonderful food you shared with us. Let’s plan to have a restaurant in the future.
Lin, thanks for the accompany when we flew to the Netherlands. I feel grateful to Bin for the train ticket booking when I first arrived. I wish you two enjoy the life in the USA.
Zhao and Yujia, thank you for the strong support and your treatment with great food. It is so nice that Yujia successfully got the CSC funding and came to Groningen. It is pity that we cannot be there together with you. Now I’m looking forward to your wedding.
As a sports man, I would like to thank all my basketball friends in Groningen. 周科，朱哥， 郭昊，威尔，王老师，丙全，欧文，大羊，大哥，道政，敏鹏，东子，王元泽，Jarvis， 贺行，还有所有一起战斗过的兄弟，thanks for your accompany every week. It is really fun to play with you. 有请下一队的队友们，尽管我们连冠失败，但是老兵不死，只是 凋零，哈哈哈哈。
Last but not least, at the most important spot, I would like to thank my family. 妈妈，感谢 您一直以来的培养与支持，您无私的奉献、无条件的信任成就了今天的我；继父，感 谢您支撑起这个家，我一路求学，您付出良多，您辛苦了；弟弟，不几年你已经要长 大了，很遗憾错过了你成长的过程，但是也很高兴我们可以一起打球了，希望你能好
146 好学习，天天向上。外婆，奶奶，孙儿不孝，没能送您们最后一程，希望您们在天堂 一切安好。Jojo, 你还在妈妈肚子里呢，希望你健康平安地来到这个世界，爸妈等你哟。 最后，亲爱的小月，你说我是你硕士最大的收获，但我想说你才是我这辈子最大的收 获。感谢你一路的追随与相伴，我会继续努力，做你最可靠的人生队友。 董京金 2021 年 3 月
