Reconfigurable sticker label electronics manufactured from nanofibrillated cellulose-based self-adhesive organic electronic materials

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from nanobrillated celluelectronic materialsJun Kawahara a,b,c, Peter AnderssHjalmar Granberg d, Magnus Bera Printed Electronics, Acreo Swedish ICT AB, Box 787, SbOrganic Electronics, Dept. of Science and TechnologycR&D Strategy Department, Lintec Corporation, 5-14-d Innventia AB, Drottning Kristinas vg 61, SE-11428 Svices, e.g. in sensor,All rights reserved.1. IntroductionSince its discovery about 2000 years ago, papers are oneof the most commonly manufactured and utilized sheetmaterials in our world; it represents the planar carrwe utilize to record, transfer and share printed intion. In fact, it is the largest surface ever manufaby mankind. During the digital revolution, paper has cer-tainly been challenged. However, nowadays, rather thanksto the digital revolution the interest for paper as the carrierfor information is regained. One of the prime reasons forthis revival is the birth of the technology and science eld1566-1199/$ - see front matter 2013 Elsevier B.V. All rights reserved. Corresponding author. Tel.: +46 11 202507.E-mail address: (P. AnderssonErsman).Organic Electronics 14 (2013) 30613069Contents lists available at ScienceDirectOrganic Ele.e l and stick approach promises for novel recongurable electronic delabel and security applications. 2013 Elsevier B.V.ier thatforma-cturedSelf-adhesiveElectronic system integrationmethod to create yet another device conguration. This is demonstrated by a stack oftwo lms that rst served as the electrolyte layer and the pixel electrode of an electrochro-mic display, which then was detached from each other and transferred to another cong-uration, thus becoming the electrolyte and gate electrode of an electrochemical transistor.Further, smart pixels, consisting of the combination of one electrochromic pixel and oneelectrochemical transistor, have successfully been manufactured with the NFC-hybridizedmaterials. The concept of system reconguration was further explored by that a pixel elec-trode charged to its colored state could be detached and then integrated on top of a tran-sistor channel. This resulted in spontaneous discharging and associated currentmodulation of the transistor channel without applying any additional gate voltage. Oura r t i c l e i n f oArticle history:Received 8 May 2013Received in revised form 10 July 2013Accepted 12 July 2013Available online 30 July 2013Keywords:Cellulose nanoberElectrochromic displayElectrochemical transistorSelf-supportinglose-based self-adhesive organicon Ersman a,, Xin Wang a, Gran Gustafsson a,ggren bE-60117 Norrkping, Sweden, Linkping University, SE-60174 Norrkping, Sweden42 Nishiki-cho, Warabi, Saitama 3350005, Japantockholm, Swedena b s t r a c tLow voltage operated electrochemical devices can be produced from electricallyconducting polymers and polyelectrolytes. Here, we report how such polymers and poly-electrolytes can be cast together with nanobrillated cellulose (NFC) derived from wood.The resulting lms, which carry ionic or electronic functionalities, are all-organic, dispos-able, light-weight, exible, self-adhesive, elastic and self-supporting. The mechanical andself-adhesive properties of the lms enable simple and exible electronic systems byassembling the lms into various kinds of components using a cut and stick method.Additionally, the self-adhesive surfaces provide a new concept that not only allows for sim-plied system integration of printed electronic components, but also allows for a uniquepossibility to detach and recongure one or several subcomponents by a peel and stickRecongurable sticker label electronics manufacturedjournal homepage: wwwctronicssevier .com/locate /orgel3062 J. Kawahara et al. / Organic Electronics 14 (2013) 30613069known as printed electronics. From an application point ofview paper now turns into the carrier for exible electron-ics, systems that can be manufactured using the sameprinting tools that were originally developed for graphicsand texts. Printed electronics dened on paper labels,package board and on ne paper, is expected to extendthe function of paper and to make paper products con-nected to the digital world.Paper is based on wood bers comprising the mostabundant organic compound derived from biomass,namely cellulose. One such renewable cellulose material,nanobrillated cellulose (NFC), has attracted a very largeinterest during the last decade. This material emanatesfrom the cellulose brils inside the wood ber wall andthe brils are liberated in different ways using both chem-ical treatment and high-pressure homogenization to sepa-rate the brils from each other and to stabilize them inaqueous dispersion [1,2]. The attraction of NFC stems fromtheir interesting intrinsic properties such as its high spe-cic surface area, exibility, high aspect ratio of the brils,good mechanical properties, and its lm forming capacity.NFC dispersions converted into nanopaper lms can betransparent, reach mechanical properties similar to thatof cast iron [3], or show very good oxygen barrier proper-ties. NFC has also been used as a ller to provide reinforce-ment, exibility and transparency in nanocomposites anddisplays [4,5].The eld of printed electronics is presently attracting alot of interest since it promises for distributed intelligenceand monitoring; features that are expected to combatsome of the challenges in our society related to health care,monitoring, logistics and safety. A tremendous variety ofcomponents have been developed and manufactured onexible substrates using different kinds of coating, printingand lamination tools [68]. Examples include batteries,capacitors, solar cells, displays, diodes, transistors and logiccircuits. To achieve true printed electronics applications,typically several different kinds of components need tobe integrated into a monolithic exible system. However,integration of printed electronic subcomponents has pro-ven to be a major challenge with respect to the mergerand compatibility of different printing technologies, mate-rials and post-processing steps. In fact, in many cases spe-cic manufacturing steps are mutually exclusive sincesome steps tend to destroy or deteriorate features andcomponents manufactured earlier in the integrationscheme. This then implies a decreased production yieldthat can only be solved by typically increasing the costfor production and integration. In addition to this, the com-plexity of such production process also brings along therequirement of huge investments of non-standard manu-facturing equipment. The overall mindset when develop-ing the printed electronics platform must therefore aimat minimizing the number of materials and process steps,as well as trying to make the processes of different sub-components compatible with each other by utilizing thesame kind of materials for different functionalities [9].One of the major advantages of using electrochemicaldevices, based on for instance an electrochemically activeconjugated polymer and an electrolyte, is that the verysame material can be used for a versatility of devicefunctions. The very same electrolyte component can beused both as the gate insulator in electrochemical andelectrolyte-gated eld effect transistors, and also as theelectrolyte in electrochromic (EC) display devices, batteriesand capacitors. PEDOT:PSS, poly(3,4-ethylenedioxythio-phene) doped with poly(styrene sulfonate acid), can serveas the conductor, display electrode and also as the transis-tor channel in printed integrated circuits, such as displays,indicators and sensor systems. The PEDOT:PSS material iselectrically conducting and optically transparent in itspristine state and it exhibits electrochromic switch charac-teristics and control of the conductivity upon electrochem-ical switching. PEDOT is a p-conjugated electronic polymerand the PSS phase serves as its counter ion [10]. In the neu-tral state PEDOT appears deep blue [11] and exhibit semi-conducting properties. PEDOT can reversibly be switchedin between its oxidized and neutral state. The electrochro-mic effect can be utilized in transmissive displays by usingtransparent electrolytes, or in a reective mode of displayoperation in which the counter electrode is hidden underan opaque electrolyte [12]. The latter version is typicallyused when PEDOT:PSS serves as both the counter and thepixel electrodes since such conguration maximizes thecolor switch contrast of the resulting display. However,there are different strategies in order to enhance the colorswitch contrast also for applications where transmissionmode is desirable, for example by using a bottom displayelectrode and a top display electrode that together expressa complementary EC switching characteristics with respectto each other. Polyaniline (PANI) is such an EC materialthat electrochemically switch color in a complementaryfashion with respect to PEDOT, i.e. it exhibits a faint yellow,close to transparent, color in its reduced leucoemeraldinestate, while PANI becomes dark blue, almost violet, in itsoxidized pernigraniline state. Hence, an electrochromicdisplay comprising a transparent electrolyte layer sand-wiched by one PEDOT:PSS electrode and one PANI elec-trode can switch between a close to transparent pixelstate to a dark black-blue colored state, where the lattercolor state is obtained by applying the positive andnegative voltage to the PANI and PEDOT:PSS electrode,respectively [13].Besides reducing the number of different materials inprinted electronics to achieve a resulting robust and ra-tional platform for exible electronics, one should alsoconsider radically new integration concepts. In packagingand graphic art industry labels are commonly adhered topaper surfaces and products to generate a nal integratedsystem or to extend the functionality of a specic product.Often, these add-on stickers include a coating that providespressure-sensitive adhesion of the label to the surface ofthe carrier. In some cases those stickers can later be re-moved and then transferred to a different new carrier oritem to serve yet another application.Previous attempts on using peel and stick or cut andstick techniques have resulted in exible thin lm solarcells [14] and free-standing dielectric layers for use in tran-sistors [15], respectively. Additionally, a novel method forintegration of memory devices onto exible substrateshas been reported [16], as well as that nanocellulose-basedcomposite materials has been examined for utilization inM.W. < 100,000), were purchased from Heraeus, Panipolwith a diameter of 50 mm and nally dried in ambientJ. Kawahara et al. / Organic Electronics 14 (2013) 30613069 3063condition for 2 days. On one of the Plyte-NFC, toluene-diluted PANI was drop cast and dried on one face (Plyte-NFC-PANI). Depending on the recipe chosen and thevolume of the mixture that is used, a wide range of thick-nesses of the resulting hybridized lms can be obtained,which in turn affect the color switch contrast and theswitching time of electrochemical devices. The P:PSS-NFClm reported here was about 25 lm thick, while the trans-parent and the opaque Plyte-NFC both were approximately300 lm thick. Three different ECD structures were createdOy, and SigmaAldrich (the last two materials), respec-tively, and used without further treatments. PET lmcoated with a 200 nm thick layer of PEDOT:PSS OrgaconEL-350 was purchased from AGFA. TiO2 powder Kronos2300 was purchased from Kronos and used as opacierin an electrolyte.Spectrophotometer (Datacolor Mercury, aperture diam-eter of 6.5 mm for the illumination, aperture diameter of2.5 mm for the measurement, SCE (specular componentexcluded) mode and D65/10 degrees illumination) wasused to measure the color contrast based on the CIEL*a*b* color coordinates. Keithley SourceMeter 2400 andHP/Agilent 4155B Parameter Analyzer were used to applyDC voltages and evaluate current vs. voltage characteristicsof the devices.2.2. Device preparationP:PSS-NFC and Plyte-NFC (transparent and opaque)were prepared by mixing the following formulations de-scribed in dry wt%: P:PSS-NFC hPEDOT:PSS/glycerol/NFC = 13.3/63.5/23.2i, transparent Plyte-NFC hPDADMAC/glycerol/NFC = 94.6/4.0/1.4i, opaque Plyte-NFC hPDAD-MAC/glycerol/TiO2/NFC = 30.8/5.9/62.4/0.9i. Solutions ofthe different materials were mixed and dispersed using aDispermill blender from ATP Engineering, about 5 ml ofeach mixture was then poured into plastic petri dishessensor applications [17]. However, the approach of thepresent study aims at functionalizing the carrier substratein order to reduce the number of materials, and thus thenumber of processing steps, and also to develop a newintegration concept for a recongurable electronic systemby using self-adhesive electronic materials to enable acut, stick and peel technology for printed electronics,i.e. to establish an electronic equivalence to the scrap-book or sticker book.2. Materials and methods2.1. Materials and equipmentAqueous dispersion of anionic carboxylated NFC(0.5 wt%, pH = 7) was prepared at Innventia AB, Sweden,according to the method described by Wgberg et al.[22]. Aqueous dispersion of PEDOT:PSS Baytron P HC, tol-uene solution of polyaniline PANIPOL T, glycerol, andaqueous solution of poly(diallyl dimethyl ammoniumchloride) (PDADMAC, polyelectrolyte with average3.1.1. Reconguration from ECD to ECTAfter characterizing the color switch contrast of theECDs shown in Fig. 2(ac), the P:PSS-NFC layer on one sideof the vertical symmetric ECD (Fig. 2(b)) was delaminatedand the remaining bilayer was cut in two pieces by using a3. Results and discussion3.1. System reconguration of electronic devicesA semi-dried membrane of NFC mixed with appropriateplasticizers exhibits gel-like behavior when it comes toappearance and physical hardness. This property ispartially remained in the fully dried state and hence aself-supporting lm can be obtained thanks to the strongscaffold functionality of NFC, which originates from hydro-gen bonds and/or ionic bonds inside the polymer matrix(not investigated further in this report), see Fig. 1. Theresulting self-supporting composite lms containing ECor electrolyte materials can weakly adhere to other solidfunctional substrate surfaces by simple lamination. Thanksto its weak adhering property the lm can also be detached(here called delaminated) from a substrate while main-taining shape and functionality. This nally results in anextremely high degree of freedom to construct, disassem-ble and reconstruct multilayered printed electronic com-ponents. For example, in this report, NFC membraneshybridized with PEDOT:PSS (labeled as P:PSS-NFC) arestacked onto NFC membranes hybridized with polyelectro-lyte and white TiO2 pigment (denoted opaque Plyte-NFC)by hand, and a vertical symmetric electrochromic display(ECD) is established by that another layer of P:PSS-NFC islaminated on the other side of the Plyte-NFC.Additionally, two other display architectures can also beprepared by simple lamination. A lateral symmetric ECD isconstructed by the lamination of two separated P:PSS-NFCon the same side of the Plyte-NFC, where the two P:PSS-NFC are physically isolated. A vertical non-symmetricECD is instead made from a drop-cast PANI layer on topof a Plyte-NFC (Plyte-NFC-PANI) and lamination of P:PSS-NFC on the opposite surface of the Plyte-NFC layer. Thesethree ECD structures are drawn in Fig. 2(ac).Upon delamination of the vertical symmetric ECD, oneof the P:PSS-NFC layers is delaminated and removed fromthe other two layers, and the remaining bilayer can insteadbe laminated onto another functional surface in order toserve as e.g. the electrolyte and the ECD pixel electrodeor the electrolyte and the gate electrode of an electrochem-ical transistor (ECT). This whole process, consisting of lam-ination, delamination and re-lamination, is here denotedsystem reconguration. Additionally, the NFC-basedfunctional lms typically are very robust and can be cutby scissors, folded or bended, hence, they have an appear-ance similar to the sticky notes used in scrapbooks or stick-er simple lamination of these hybridized lms. The colorswitch contrast of each ECD was characterized by the spec-trophotometer after connecting both electrodes to a DCpower supply.nation of the ECD, one P:PSS-NFC layer is fully oxidizedsurement is performed by obtaining the CIE color spaced PED3064 J. Kawahara et al. / Organic Electronics 14 (2013) 30613069pair of scissors. One of the cut pieces was manually lami-nated onto a PEDOT:PSS-based ECT channel prepared froman Orgacon EL-350 lm patterned by a knife plotter tool.Here the laminated bilayer served as the gate electrodeand the electrolyte layer of an ECT, and the patterned PED-OT:PSS on top of the PET substrate served as the drain,source and channel material, see Fig. 2(e). The other cutpiece was put onto another Orgacon foil such that colorswitching could be observed in order to prove the recong-uration concept (data not recorded), see Fig. 2(f).3.1.2. ECT characterizationThe structure of the resulting ECT is drawn in Fig. 3,although the schematic illustration shows a complete elec-trochromic smart pixel device that will be discussed later.Instead of completing the EC smart pixel device by prepar-ing the top electrode of the ECDmoiety, the ECT is obtainedby connecting a DC power supply to the drain electrodesuch that the IV curves of the ECT could be recordedseparately.3.1.3. Reconguration from ECT to EC smart pixelThe ECT characterized in Section 3.1.2 was further dis-assembled by delamination of the gate electrode bilayer.In combination with another piece of bilayer, which ismentioned in the end of Section 3.1.1 above, the two lmswere laminated onto another similarly patterned Orgaconlm in order to create an EC smart pixel device, seeFigs. 2(g) and 3. In this report an EC smart pixel is denedas an ECD connected in series with an ECT, hence, the ECDcoloration can be controlled by the conduction state of theaddressing ECT. Here, upon reconguration, one of theFig. 1. Photographs showing the self-supporting lms based on (a) NFC anpolyelectrolyte.laminated bilayers served as the gate electrode and theother was used as the pixel top electrode.3.1.4. EC smart pixel characterizationThe same external circuitry was connected as in thecase of ECT characterization, except for that the pixel topelectrode, and not the drain electrode, was connected tothe equipment. The EC smart pixel characterization meth-od has been reported previously [12].3.1.5. Reconguration and duplication of the EC smart pixelThe two bilayers of the EC smart pixel device describedin Section 3.1.3 serve as the gate and the ECD pixel elec-trodes, and after delamination they were laminated ontovalues L*, a* and b* of the pixel electrode. Finally the colorcontrast value DE* is calculated from the following equa-tion [18,19]:while the other P:PSS-NFC layer is in its fully reduced state.The bilayer including reduced PEDOT:PSS was then recon-gured and transferred onto a PEDOT:PSS-based ECT chan-nel such that the bilayer instead became the electrolyteand the gate electrode of an ECT. However, in this casethe gate electrode is not connected to any power supply;it is only wired directly to the source electrode. So, sincethe gate electrode was electrochemically reduced in ad-vance, it is expected that this charge will be equilibratedbetween the gate and the ECT channel, hence, currentmodulation of the ECT channel should occur just uponbringing the sheets into contact with each other.3.2. Device characteristics3.2.1. Color switch contrast of the ECDEC pixels with three different architectures (Fig. 2(ac))were evaluated and the data is shown in Table 1. The mea-another Orgacon lm having the same pattern in order tocreate the same EC smart pixel architecture as in Section3.1.3, which was characterized according to Section Reconguration of a pre-charged hybridized NFC-basedlayerA vertical symmetric ECD was prepared according toFig. 2(b), followed by applying a voltage across the ECD,which in turn results in electrode charging. After delami-OT:PSS, (b) NFC and transparent polyelectrolyte, and (c) NFC and opaqueDE L2 L12 a2 a12 b2 b12qHere the subscripts 1 and 2 for each color spaceparameter indicate the decolored (oxidized light blue)and colored (reduced deep blue) states of the PEDOT pixelelectrode, i.e. the on and off states, respectively. The high-est color contrast was obtained in a lateral pixel device;DE* = 35.2. This is somewhat lower as compared to re-cently reported PEDOT:PSS-based EC pixel devices [20].However, the obtained color contrast is considered to besufcient for most display applications. The color contrastresults and the appearances of the characterized displaysare shown in Table 1 and Fig. 4.J. Kawahara et al. / Organic Electronics 14 (2013) 30613069 3065(a) (b)3.2.2. ECT characteristicsThe currentvoltage (IV) output curves for the ECTdevice (Fig. 2(e)) are shown in Fig. 5. The ECT is operating(d) (e)(g)Fig. 2. Device structures and manufacturing, reconguration and characterizatiovertical symmetric ECD and the complementary vertical non-symmetric ECD is shECD are ionically connected by either a transparent, (a) and (c), or an opaquereconguration of a pre-charged (b) electrode that is applied onto an ECT channethe (b) pixel electrode into an ECT gate electrode on top of a patterned ECT cmaintained after reconguration. To fully demonstrate the concept, the color stasmart pixel device (g), which is obtained by delamination and reconguration ofby simply duplicating the EC smart pixel device onto another substrate by utilizincharacteristics as compared to device (g).(c)in depletion mode, which implies that the maximumon-current through the transistor channel is obtainedwhen the gate voltage (VG) is 0 V. This is due to that the(h)(f)n procedures are summarized in this chart. The lateral symmetric ECD, theown in (a), (b) and (c), respectively. The electrochromic electrodes of each, (b), electrolyte layer. (d) shows an ECT achieved by delamination andl patterned on top of a PET foil. The ECT in (e) is created after reconguringhannel on a PET foil, while (f) proves that the ECD functionality can bete of an ECD can be controlled by the conduction state of an ECT in an ECthe (f) subcomponent onto the (e) device. Finally, this is further evidencedg the reconguration technique (h) and thereafter recording identical IV3066 J. Kawahara et al. / Organic Electronics 14 (2013) 30613069Fig. 3. The top view of the ECT/EC smart pixel is illustrated. The drain andsource electrodes are 20 20 mm2 squares and they are connected by anarrow rectangle having an area of 0.4 10 mm2. Approximately 3 mm ofthe length of the rectangle is covered by the electrolyte and the gateelectrode bilayer, thereby forming the active area of the ECT channel,2PEDOT:PSS is electrically conducting in its pristineoxidized state, hence, the channel is switched to its off-state upon applying a positive VG. Here the electric currentthrough the channel between the drain and source elec-trodes (IDS) was recorded by sweeping the drain-sourcevoltage (VDS) from 0 to 1.0 V at an incremental step of0.01 V for 6 different VG; 0 V at the rst cycle and thenincreased in steps of 0.25 V until the last sweep at 1.25 V.The minimum off-current level is reached already atVG = 0.75 V, which can be observed by that the curves rep-resenting VG = 0.75, 1 and 1.25 V behave similarly, see insetof Fig. 5. The time between two adjacent data points was10 ms. An on/off-ratio of approximately 100 was observedand the off-current level was about 6080 nA. Both thesevalues, especially the low off-current, are sufcient forthe operation of an active matrix addressed display, seenext section. Previous research projects related to PED-OT:PSS-based ECTs and ECDs have shown a number ofswitch cycles exceeding 104 and 105, respectively, there-fore we have no reason to believe that the devices reportedherein would behave differently, even though no evalua-tion of the operational lifetime was performed. However,while an area of 2 2 mm of the bilayer sheet was attached at the edgeof the drain electrode such that the bilayer serves as the coloring pixelelectrode and the drain electrode serves as the counter electrode of the ECsmart pixel device. Note that the VDS is connected between the drain andsource electrodes in the case of an ECT measurement, while the sourceand pixel electrodes are connected in the EC smart pixel measurement.Table 1ECD color switch contrast measurements based on CIE L*a*b* colorcoordinates. The numbers 1 and 2 indicated by the subscripts beside L*,a* and b* represent the decolored (oxidized light blue) and the colored(reduced deep blue) state of the pixel top electrode, respectively.Device L1 a1 b1 L2 a2 b2 DE*(a) 58.16 4.05 7.55 28.83 0.22 26.68 35.2(b) 63.48 4.08 6.10 43.39 1.49 21.19 25.3(c) 37.15 12.7 3.48 17.28 3.23 17.2 30.2the ECT device did not show any issues regarding delami-nation or degradation upon storage in ambient atmosphere(22 C and 40%RH) for 1 month. Fig. 6 shows an ECT mea-sured 19 and 31 days after device assembly. The relativelyconstant on- and off-current levels of the ECT demonstratehigh degree of stability over extended periods of time.3.2.3. EC smart pixel: Integration of ECD and ECTThe function of the EC smart pixel, which herein is de-ned as the circuit integration of one ECT and one ECD, isvalidated by using two previously reported measurementmethods [12]. The two methods are chosen in order toinvestigate the two-folded functionality of the ECT in thesmart pixel conguration; prevention of cross-talk alongFig. 4. Photographs showing two different display architectures that havebeen characterized: (a) lateral symmetric ECD based on two P:PSS-NFCelectrodes bridged by Plyte-NFC, and (b) complementary vertical non-symmetric ECD consisting of Plyte-NFC sandwiched by one layer of P:PSS-NFC and a drop cast layer of PANI. No photograph is available for thevertical symmetric ECD based on opaque Plyte-NFC sandwiched by P:PSS-NFC on both sides.-0.10-0.09-0.08-0.07-0.06-0.05-1.0 -0.5 0.0-8-7-6-5-4-3-2-10-1.0 -0.8 -0.6 -0.4 -0.2 0.0VDS / VI DS / AFig. 5. IV characteristics of an ECT utilizing Orgacon as the transistorchannel and the drain and source electrodes, Plyte-NFC as the electrolyteand P:PSS-NFC as the gate electrode. The inset graph indicates the off-current levels at elevated gate voltages.the addressing lines of the ECD devices in an active-matrixdisplay and to improve the retention time of an ECD thathas been updated to its colored state. The former is evalu-ated by monitoring that the pixel does not switch from itstransparent off-state to its colored on-state upon applyingVDS and VG (the ECT is in its off-state) simultaneously. Thethanks to their electrochemical and impedance character-istics. Further, the ability to control the color state of eachEC pixel in a larger system is advantageous; not only be-tween the on- and off-states but also to enable gray-scalelevels. Here, the negative current peaks in Figs. 7 and 8 cor-respond to electrochemical reduction, i.e. switching to thenon-conducting state and deep-blue coloration, of the PED-OT:PSS-based ECT channel or EC pixel electrode, while thepositive current peak instead represents oxidation into the-10-8-6-4-20-1.0 -0.5 0.0-0.04-0.03-0.02-0.01-1.0 -0.5 0.0VDS / VI DS /AFig. 6. An ECT showing identical IV characteristics 19 (left) and 31 (right) days acurrent levels at elevated gate voltages.-25-200 20 40 60 80Time /sCurrFig. 8. The ECT shows its capability to maintain the color state of the ECD.First, the pixel is switched to its colored state by VDS, which is shown inthe rst current peak at t 3 s. Subsequently VG is set to 1 V and thetransistor channel switches off to its reduced state at t 20 s, whichgenerates the second current peak. At t 32 s VDS is set to 0 V, whichresults in maintained color even though a small leakage current can beobserved. When VG is set to 0 V at t 43 s, the ECD is decolored by thedischarging current indicated by the positive current peak.J. Kawahara et al. / Organic Electronics 14 (2013) 30613069 3067latter feature can be evaluated by applying VG after switch-ing the ECD to its on-state, followed by turning off VDS,which results in color retention of the ECD introduced bythe non-conducting off-state of the ECT channel. Figs. 7and 8 show the results of the two ECTECD smart pixelfunctionalities.Fig. 7 indicates that the ECD is switched on only whenVDS is turned on and when VG is 0 V (the ECT is in its on-state), as evidenced by the low leakage current owthrough the EC smart pixel while the ECT channel is non-conducting. This is a required feature in order to preventcross-talk effects along the EC pixel addressing lines inan active matrix addressed EC display; only one ECT perEC pixel addressing line is allowed to be in its conductingstate. Fig. 8 demonstrates that the conduction state cancontrol the retention time of the EC pixel. This has a directimpact on the power consumption in large active-matrixdisplay systems. EC pixels are semi-bistable to their nature,-6-4-20the pixel /A-30-15015300 20 40 60ChargingDischarging-20-18-16-14-12-10-80 20 40 60 80Time /sCurrent through Fig. 7. The ECT shows that it can prevent ECD cross-talk. The rst currentpeak at t 10 s corresponds to electrochemical reduction of the channelinto its non-conducting state by applying VG. VDS was applied at t 25 sbut no current peak due to pixel coloration can be observed, whichindicates that the off-state of the ECT is capable of keeping the ECD in itsinitial off-state. Finally, VG = 0 V is applied at t 45 s, which brings theECT channel to its on-state that, in turn, allows for pixel coloration by theconstantly applied VDS. The inset graph shows the charging and discharg-ing behavior of an independent ECD.-10-8-6-4-20-1.0 -0.5 0.0VDS / VI DS / A-0.05-0.04-0.03-1.0 -0.5 0.0fter device manufacturing, respectively. The inset graphs indicate the off--15-10-50510152025ent through the pixel / Aconducting and transparent form of the PEDOT:PSS in theECT channel or EC pixel electrode. The area dependenceon the switching time can be observed in the graphs; therelatively narrow current peaks correspond to the redoxreactions of the ECT channel and the relatively broadercurrent peaks represent color updates in the EC pixel.The switching time of the EC pixel is typically prolongedby high strain on the ECT channel, i.e. by simultaneouslyapplying VDS and VG results in a reduction front propagat-ing within the PEDOT:PSS channel outside the electrolyteedge. This is reected in the broadened coloration currentpeak starting at t 45 s in Fig. 7. There are several avail-able routes how to circumvent the issue with long switch-ing times in ECTs and EC smart pixels, this is however notthe focus of the present work [21].By combining the measurements and results given inFigs. 7 and 8 we draw the conclusion that the color stateof the EC pixel can be properly controlled by the appliedgate voltage to the ECT device, and practically no leakagecurrent is observed.3.2.4. Reconguration test of NFC-hybridized electrochemicaldevicesVarious kinds of electronic devices have been estab-lished by combining nanobrillated cellulose (NFC) witheither a polyelectrolyte or a conducting polymer, e.g. elec-trochromic displays, electrochemical transistors, electro-chromic smart pixels and even electrolyte capacitors;components that together as integrated systems can formlarger electronic systems, such as active matrix addresseddisplays, indicators, sensors and more. The devices ob-tained here utilize NFC in order to create ionically and elec-tronically conducting lms that are self-supporting, i.e.functionalized substrates. In addition to this, it is also pos-sible to integrate, disintegrate and recongure the initiallydevices.more advanced exible electronic circuits.gate electrode was pre-charged adjacently to the ECT device, peeled off3068 J. Kawahara et al. / Organic Electronics 14 (2013) 30613069and recongured on top of the ECT channel. Before laminating the pre-charged gate electrode and its electrolyte layer, IDS 55 lA can beobserved during the rst few seconds of the measurement. Uponreconguration of the charged gate electrode, IDS decreases to 10 lA;far from the most optimized on/off-ratio in terms of transistor perfor-mance but yet it proves the concept of system integration, recongura-tion and energy transfer by using the peel and stick technique.created subcomponents by using a cut, stick and peeltechnique similar to what is being used in a sticker book.Reconguration of the gate electrode and the pixel elec-trode in the respective ECT and EC smart pixel devices,which resulted in a second set of devices, showed mostlyidentical performance as compared to the rst set of de-vices shown in Figs. 5, 7 and 8 (data not shown). This dem-onstrates the robustness of the interfaces that areestablished upon reconguration of the functionalizedsubstrates.The system integration concept is also demonstrated bythe measurement shown in Fig. 9. An electrochemicalcapacitor is formed by using a layer of Plyte-NFC as theintermediate layer, Orgacon as one of the electrodes anda layer of PEDOT:PSS-NFC as the other electrode. The latterelectrode is then electrochemically reduced by applying avoltage of 5 V for 10 s. The capacitor structure was thenpeeled apart by separating the bilayer from the Orgaconsheet, and the remaining bilayer was instead recongured-80-60-40-2000 20 40 60 80 100Time /sI DS /AFig. 9. The graph shows the current modulation of an ECT channel. TheAcknowledgementsThis work was supported by the Knut and AliceWallenberg Foundation (Power Papers).References[1] D. Klemm, F. Kramer, S. Moritz, T. Lindstrm, M. Ankerfors, D. Gray,A. Dorris, Nanocelluloses: a new family of nature-based materials,Angewandte Chemie International Edition 50 (2011) 54385466.[2] S.J. Eichhorn, A. Dufresne, M. Aranguren, N.E. Marcovich, J.R.Capadona, S.J. Rowan, C. Weder, W. Thielemans, M. Roman, S.Renneckar, W. Gindl, S. Veigel, J. 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An electro-chromic display pixel without ordinary plastic substrate(e.g. PET lm), an electrochemical transistor where theNFC hybrid layers stick to the solid PEDOT:PSS channeland an electrochromic smart pixel composed of one pixeland one transistor were all successfully achieved. The com-ponents functioned well after performing the peel andstick reconguration of the NFC layers, and they alsoshowed very good stability with respect to storage timein ambient atmosphere. The unique ability to integrateand recongure electronic systems based on self-support-ing subcomponents will pave the way for the creation ofcient to alter the conduction state of the ECT device. 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Kawahara et al. / Organic Electronics 14 (2013) 30613069 3069Reconfigurable sticker label electronics manufactured from nanofibrillated cellulose-based self-adhesive organic electronic materials1 Introduction2 Materials and methods2.1 Materials and equipment2.2 Device preparation3 Results and discussion3.1 System reconfiguration of electronic devices3.1.1 Reconfiguration from ECD to ECT3.1.2 ECT characterization3.1.3 Reconfiguration from ECT to EC smart pixel3.1.4 EC smart pixel characterization3.1.5 Reconfiguration and duplication of the EC smart pixel3.1.6 Reconfiguration of a pre-charged hybridized NFC-based layer3.2 Device characteristics3.2.1 Color switch contrast of the ECD3.2.2 ECT characteristics3.2.3 EC smart pixel: Integration of ECD and ECT3.2.4 Reconfiguration test of NFC-hybridized electrochemical devices4 ConclusionsAcknowledgementsReferences


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