Linköping Studies in Science and Technology Dissertations No. 1942 Screen Printing Technology for Energy Devices Andreas Willfahrt 2019 Norrköping © Andreas Willfahrt, 2019 Printed in Sweden by LiU Press ISSN 0345-7524 ISBN 978-91-7685-274-3 Screen Printing Technology for Energy Devices by Andreas Willfahrt February 2019 ISBN 978-91-7685-274-3 Linköping Studies in Science and Technology Dissertation No. 1942 ISSN 0345-7524 Dedicated to my family, my three gorgeous girls. Abstract The technical application of screen and stencil printing has been state of the art for decades. As part of the subtractive production process of printed circuit boards, for instance, screen and stencil printing play an important role. With the end of the 20th century, another field has opened up with organic electronics. Since then, more and more functional layers have been produced using prin- ting methods. Printed electronics devices offer properties that give almost every freedom to the creativity of product development. Flexibility, low weight, use of non-toxic materials, simple disposal and an enormous number of units due to the production process are some of the prominent keywords associated with this field. Screen printing is a widely-used process in printed electronics, as this pro- cess is very flexible with regard to the materials that can be used. In addition, a minimum resolution of approximately 30 µm is sufficiently high. The ink film thickness, which can be controlled over a wide range, is an extremely important advantage of the process. Depending on the viscosity, layer thicknesses of several hundred nanometres up to several hundred micrometres can be realised. The conversion and storage of energy is an important topic, either in the field of renewable energies or the energy supply of the Internet of Things (IoT). This thesis addresses the print production of both device classes. Vertically structured thermoelectric generators (TEGs) for energy conversion and stacked supercapacitors for energy storage are produced by screen printing. Papers I-IV focus on the generation of functional layers of vertically alig- ned thermoelectric generators. These can convert heat directly into electrical energy. The vertical design was chosen due to the simple application of the de- vice at the heat source. The general feasibility of screen-printed, vertically alig- ned TEGs was demonstrated. Optimisation of the thermoelectric materials is required, so that the process can be used sensibly. In paper III, the Ni containing model ink was optimised for filling the cavities in the insulator layer. In paper IV the printed thermoelectric generators are modelled. The performance of a set of parameters can be estimated by this model. The high Seebeck coefficient of ionic conductors is used in paper V in so-called ionic thermoelectric superca- pacitor (ITESC), a combination of TEG and supercapacitor. Paper VI presents an environmentally friendly supercapacitor with a printable separator based on cornstarch and citric acid, which has a competitive electrochemical performance compared to printed supercapacitors reported elsewhere. In paper VII, some parameters of screen-printed primary Zn/MnO2 cells are optimised and a prin- table separator based on cornstarch and lactic acid was successfully tested. Populärvetenskaplig sammanfattning Den tekniska tillämpningen av skärm- och stencilutskrift har varit topp- moderna i årtionden. Som en del av den subtraktiva produktionsprocessen av tryckta kretskort spelar exempelvis skärm- och stencilutskrift en viktig roll. I slutet av 1900-talet har ett annat fält öppnat med organisk elektronik. Sedan dess har allt fler funktionella lager producerats med hjälp av tryckmetoder. Tryckta elektronikanordningar erbjuder egenskaper som ger nästan all frihet till kreati- viteten i produktutvecklingen. Flexibilitet, låg vikt, användning av giftfria mate- rial, enkelt bortskaffande och ett enormt antal enheter på grund av produktions- processen är några av de framträdande nyckelord som hör till detta område. Skärmtryck är en allmänt använd process i tryckt elektronik, eftersom pro- cessen är mycket flexibel med avseende på material som kan användas. Dessutom är en minsta upplösning på cirka 30 µm tillräckligt bra. Bläckfilmens tjocklek, som kan styras över ett brett område, är en extremt viktig fördel med processen. Beroende på viskositeten kan skikttjockleken på flera hundra nanometer upp till flera hundra mikrometer realiseras. Omvandling och lagring av energi är ett viktigt ämne, antingen inom för- nybara energikällor eller energiförsörjningen av saker i saken (IoT). Denna av- handling riktar sig till utskriftsproduktionen av båda enhetsklasserna. Vertikalt strukturerade termoelektriska generatorer (TEG) för energiomvandling och sta- plade superkapacitorer för energilagring produceras genom skärmutskrift. Publikationer I-IV fokuserar på generering av funktionella lager av verti- kalt inriktade termoelektriska generatorer. Dessa kan omvandla värme direkt till elektrisk energi. Den vertikala konstruktionen valdes på grund av enkel anord- ning av anordningen vid värmekällan. Det generella genomförbara av skärm- tryckta vertikalt anpassade TEG-skivor visades. Optimering av termoelektris- ka material krävs, så att processen kan användas förnuftigt. I publikation III optimerades den Ni-innehållande modellfärgen för fyllning av kaviteterna i isolatskiktet. I publikation IV modelleras de tryckta termoelektriska generato- rerna. Utförandet av en uppsättning parametrar kan beräknas med denna mo- dell. Den höga Seebeck-koefficienten för jonledare används i publikation V i så kallad jonisk termoelektrisk superkapacitor (ITESC), en kombination av TEG och superkapacitor. Publikation VI presenterar en miljövänlig superkapacitet med en utskrivbar separator baserad på majsstärkelse och citronsyra, som har en konkurrenskraftig elektrokemisk prestanda jämfört med tryckta superkapa- citorer som rapporterats någon annanstans. I publikation VII optimeras vissa parametrar av skärmtryckta primära Zn / MnO2-celler och en testbar separator baserad på majsstärkelse och mjölksyra testades med framgång. Acknowledgements “The journey is the reward” Confucius comes closest to german aphorism “Der Weg ist das Ziel”. This sentence best de- scribes how I feel about my doctoral thesis, which is now being completed. The journey was longer than I initially thought, but with the proverb in mind I was more blessed than ‘condemned’ by this long journey. I would like to thank all nameless helpers who have their share in the back- ground or directly in the PhD thesis. To list all the names would go beyond the scope, but some really deserve special thanks, this applies to the following peo- ple, in alphabetic order: Annelie, Chris, Dan, Florian, Hui, John, Jonas, Karin, Katarina, Michael, Michl, Olga, Skomantas, Sophie, Thomas, and Zia. Frank for ink donations and discussions, Prof. Weidenkaff and Prof. Ludwigs at Stuttgart University for discussions and precious lab-time as well as their co-workers Anna and Marc for help and expertise. I met a lot of people in the course of this PhD, and I learned a lot from every single person. Still, there are some people outstan- ding, since they accompanied this long journey all the way long. These people deserve my sincere and deep gratitude: Xavier Crispin, the supervisor and motivator of this research work, who is a great person and scientist and thus a valuable conversation partner and innova- tor. His pursuit to the limit is laborious, but it allows a high quality result to be delivered. His great support over the last year has made it easier to reach the goal. And that is not the only reason why I owe him so much. Erich Steiner, co-supervisor at Stuttgart Media University, who actively accom- panied the entire journey. Together we learned a lot about new topics in the lectures. And as the outstanding teacher he is, he has decisively shaped the work through countless discussions and lessons. Isak Engquist, co-supervisor at Linköping University, beginning with the phase of the PhD after the licentiate degree. He was also always open minded and an equally valuable conversation partner for lively discussion. Gunter Hübner, co-supervisor at Stuttgart Media University, who provided the administrative framework and the financial basis for the research work. “It does not matter how slowly you go as long as you do not stop." Confucius Stuttgart/Norrköping, February 2019 Andreas Willfahrt Publications included in the Thesis Paper I: Optimising Stencil Thickness and Ink Film Deposit Andreas Willfahrt, John Stephens, Gunter Hübner International Circular of Graphic Education and Research, 4, pp.6-17, 2011 Contribution: All the conceptual and most of the experimental work. Wrote the first draft and was involved in the final editing of the paper. Paper II: Optimization of aperture size and distance in the insulating mask of a five layer vertical stack forming a fully printed thermoelectric generator Andreas Willfahrt, Gunter Hübner Advances in Printing and Media Technology, Vol. 38, pp. 261–269, 2011 Contribution: All the conceptual and most of the experimental work. Wrote the manuscript and did the final editing of the paper. Paper III: Screen printing into cavities of a thick insulating layer as a part of a fully prin- ted thermoelectric generator Andreas Willfahrt, Jochen Witte, Gunter Hübner Proc. Int. Circle of Educational Institutes for Graphic Arts (IC), Sept 2011, Norrköping, Sweden. Contribution: All the conceptual and most of the