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Flexible electronic systems such as wearable devices, sensors and electronic skin require power sources and sensing units that are mechanically robust, operational at low bending radius, and environmentally friendly. Recently, there has been an enormous interest in active materials such as thin film semiconductors, conductive polymers, and ion-electron conductors. These materials can be deposited with both printing and microfabrication techniques onto the flexible substrates such as plastics and paper. In addition, paper-based composites with nanofibrillated cellulose are favorable due to their mechanical strength, porosity, and solution-processability. Printing of such systems enables mass-production of large area electrochemical devices i.e., batteries, supercapacitors and fuel cells. Moreover, designing ultrathin devices for such concepts are promising for implantable and skin-like conformable electronics. The aim of this thesis is the development of flexible electronic devices where, both organic and inorganic materials are explored, and examples of smart packaging and wearable electronics are demonstrated. Within the thesis, two different fabrication approaches are presented to achieve flexible electronics: (1) fabrication of porous paper electrodes for printable, wearable supercapacitor applications, where our efforts towards sustainable solutions for energy storage and (2) development of ultraflexible devices for electronic skin and implantable electronics to attain miniaturized, ultrathin device concepts. Overall, high performance electronic devices and demonstrators shown here have a significant impact on portable hybrid systems and flexible electronics applications. Flexibla elektroniska system såsom kroppsburna enheter, sensorer och elektronisk hud kräver strömkällor och sensorenheter som är mekaniskt robusta, fungerar i böjt tillstånd och är miljövänliga. På senare tid har detta lett till ett enormt intresse för aktiva material som tunnfilmshalvledare, ledande polymerer och kombinerade jon- och elektronledare. Dessa material kan deponeras med både tryck- och mikrotillverkningstekniker på flexibla substrat som plast och papper. Vidare är pappersbaserade kompositer med nanofibrillerad cellulosa intressanta på grund av deras mekaniska styrka, porositet och möjlighet att processa i lösning. Tryckning av sådana system möjliggör massproduktion av elektrokemiska enheter med stor yta, dvs batterier, superkondensatorer och bränsleceller. För att ge hudliknande formbarhet och biokompatibilitet för implanterbara enheter är ultratunna enheter ett lovande koncept. Syftet med denna avhandling är att utveckla flexibla elektroniska enheter där både organiska och oorganiska material utforskas, och att demonstrera exempel på smarta förpackningar och kroppsburen elektronik. I avhandlingen presenteras två olika tillverkningsmetoder för flexibel elektronik: (1) tillverkning av porösa papperselektroder för tryckbara, kroppsburna superkondensatorer, syftande till hållbara lösningar för energilagring och (2) utveckling av ultraflexibla enheter för elektronisk hud och implanterbar elektronik för att uppnå miniatyriserade, ultratunna enhetskoncept. Sammantaget kan de högpresterande elektroniska enheter och demonstratorer som visas här ha stor betydelse för utvecklingen av bärbara hybridsystem och flexibel elektronik.

Enerji ihtiyacı yakın geleceğimizin en önemli problemlerinde biri olarak görülüp, düşük enerji sarf eden ve kendi enerjisini kendi üreten esnek elektronik cihazlar dünyanın enerji ihtiyacını azaltabilir. Bu sorunun üstesinden gelmek için fonksiyonel ve enerji verimli malzemeler çözüm olarak sunulmaktadır. Seri üretimle uyumlu, kolay üretebilen, ucuz ve toksik olmayan, yüksek piezoelektrik sabite sahip malzemeler üretmek, hassas sensör ve kendi enerjisini üreten cihazlar tasarlamak amacıyla yüksek talep görmektedir. Bu tezde piezoelektrik polimer (PVDF-TrFE) tabanlı, protez el, kardiyak sensoru ve yapay (elektronik) deri gibi çeşitli sensor tipleri ve enerji üreten/depolayan cihazlar, esneyebilen elektronik için gelecek vaat eden cihaz yapıları gösterilmiştir. Yarı-iletken, metal, kompozit, piezoelektrik malzemeler ve polimerler fiber çekme yöntemiyle üretilebilip olup, ardışık boyut küçültme tekniği ile bu malzemelerin geometrileri, boyutları ve uzunlukları kontrol edilebilir ve bu teknik özgün, fiber içinde ve fiber-dizi cihazları nano boyutta tasarlamamızı sağlar. Bu tezde öncelikle, PVDF-TrFE fiber performansını arttırmak için yeni tasarımlar ortaya koyarak fiberlerin kristal yapısı artırıldı ve faz geçiş sistemi incelendi. Son olarak, esnek iletken elektronik bağlar ve elektrot uygulamaları için iletken kompozit malzeme üretildi. Sonuç olarak, özgün piezoelektrik ve kompozit fiberler ardışık boyut küçültme tekniği kullanılarak üretildi ve esnek elektronik uygulamaları için fiber cihazlar tasarlandı. Fabricating low energy requiring and self-powered flexible electronic devices can decrease world energy need since energy demand seems to be one of the most fundamental problems in the near future. An excellent solution to overcome this drawback is fabricating functional and energy efficient materials. Fabricating high piezoelectric coefficient materials that are compatible with mass production, easy to produce, low cost and non-toxic is highly demanded in order to design highly sensitive sensors and self-powered devices. This thesis introduces piezoelectric polymer (PVDF-TrFE) based several sensor types, energy harvesting devices such as; prosthetic hand, cardiac sensors, electronic skin, which represent promising device architectures for flexible electronics. Semiconductor, metal, composite, piezoelectric materials or polymers can be drawn by thermal fiber drawing and by applying iterative size reduction technique, the geometry, size and length of fabricated structures can be controlled, which also enables us to design novel in fiber, fiber-array devices at nanoscale. First, to enhance PVDF-TrFE fiber performance, crystallinity of fibers was improved by introducing new designs and phase transition mechanism was investigated in fabricated films and fibers. Finally, conductive composite material for flexible interconnects and electrodes was developed. As a whole, a variety of novel piezoelectric and conductive composite fibers were fabricated by using novel size reduction technique and fiber devices were designed for flexible electronics applications. 100

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