reading

Cover
Dedication
About the Series Editor
Preface
1 Soft Composites with Tunable Optical and Electrical Properties
1. 1.1 Introduction
2. 1.2 Soft Color Composites
3. 1.3 Hybrid Viscoelastic Polymer Composites
4. 1.4 Elastomeric Conductive Composites
5. 1.5 Conclusions and Future Perspectives
6. Acknowledgments
7. References
2 Organic Semiconductors for Transparent Electronics
1. 2.1 Introduction
2. 2.2 Optically Transparent Semiconductor Families
3. 2.3 Conclusions and Perspectives
4. References
3 Flexible Carbon‐based Electronics: Flexible Solar Cells
1. 3.1 Introduction
2. 3.2 Applications
3. 3.3 Device Physics
4. 3.4 New Materials
5. 3.5 Flexible Electrodes
6. 3.6 Processing
7. 3.7 Summary and Outlook
8. References
4 Development of Organic Field‐effect Transistors for Operation at High Frequency
1. 4.1 Introduction
2. 4.2 The Transition Frequency f _t
3. 4.3 High‐frequency Organic Field‐effect Transistors
4. 4.4 Conclusions and Perspectives
5. References
5 Graphene for Flexible Electronics
1. 5.1 Introduction
2. 5.2 Synthesis and Transfer Process
3. 5.3 Applications
4. 5.4 Conclusions and Perspectives
5. References
6 Printing 2D Materials
1. 6.1 Introduction
2. 6.2 Printing Techniques
3. 6.3 Formulation and Characterization of Electronic Inks
4. 6.4 Exfoliation of Layered Crystals
5. 6.5 Stabilization of Exfoliated Flakes
6. 6.6 Formulation: From Dispersion to Ink
7. 6.7 Printing and Coating of 2D‐crystal‐based Inks
8. 6.8 Applications
9. 6.9 Outlook and Future Perspectives
10. Acknowledgments
11. References
7 Characterization of Graphene Flexible Materials and Displays
1. 7.1 Introduction to Display Systems
2. 7.2 Graphene/Flexible Polymer Electrodes
3. 7.3 Graphene‐based Flexible Displays
4. 7.4 Outlook
5. References
8 AMOLED Display Technology and Applications
1. 8.1 Introduction
2. 8.2 Commercial Flexible AMOLED Displays
3. 8.3 OLED Displays
4. 8.4 AMOLED Display Design
5. 8.5 Substrates and Barrier Coatings
6. 8.6 The Future of Flexible AMOLED Displays
7. References
9 Flexible Batteries
1. 9.1 Introduction
2. 9.2 Electrochemical Power Sources – Theoretical Basics
3. 9.3 Basic Material Concepts for Flexible Energy Storage Systems
4. 9.4 Basic Design Concepts for Flexible Energy Storage Systems
5. 9.5 Summary and Outlook
6. References
10 Flexible Organic Bioelectronics and Biosensors
1. 10.1 Introduction
2. 10.2 Organic Material
3. 10.3 Flexible Organic Electronics for Biology
4. 10.4 Conclusion
5. References
Index
End User License Agreement

List of Tables

Chapter 02
1. Table 2.1 Summary of the absorption maxima (λ _max),a absorption onset (λ _onset), optical band gap (E _g ^opt), field‐effect mobilities (μ)b, and current I _on/I _off ratios in a particular transistor device structurec for organic semiconductors reviewed in this chapter.
Chapter 03
1. Table 3.1 Overview of high impact PSC donor polymers and performance; PTB7: poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]]; PV5001: trade name from Raynergy Tek Incorporation – unpublished structure; PBTZT‐stat‐BDTT‐8: poly[(5,6‐bis‐R1‐(2,1,3‐benzothiadiazole‐4,7‐diyl)‐thiophene‐2,5‐diyl)‐stat‐(4,8‐bis‐R2‐(benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl)‐thiophene‐2,5‐diyl)], side chains R1 and R2 are not published (trade name from Merck: lisicon); PffBT4T‐C₉C₁₃: (poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3‴‐di(2‐nonyltridecyl)‐2,2′;5′,2″;5″,2‴‐quaterthiophen‐5,5‴‐diyl)]).
2. Table 3.2 Overview of the most relevant semitransparent flexible electrode materials for OPV applications.
Chapter 06
1. Table 6.1 Printed electronics with pristine graphene.
2. Table 6.2 Printed electronics with other 2D materials such as , , and h‐BN.
Chapter 07
1. Table 7.1 Sheet resistance (R _s), transmittance (T), and the maximum applied strain or the radius of curvature that the flexible electrode can withstand without affecting the R _s values for various graphene/flexible polymer electrodes systems.
Chapter 08
1. Table 8.1 The first products to use flexible AMOLED displays.
2. Table 8.2 TFT requirements of AMLCD, active matrix electrophoretic, and AMOLED displays.
3. Table 8.3 The primary TFT technologies for displays, with their characteristics relevant for AMOLED displays.
4. Table 8.4 Gas transmission properties for common polymer films.
Chapter 09
1. Table 9.1 Applications of carbon in different battery chemistries.

List of Illustrations

Chapter 01
1. 1.1 (a) PS (polystyrene)–PMMA (polymethyl methacrylate)–PEA (polyethylacrylate) core–shell opaline sphere. (b) The PET–opaline spheres–PET film after rolling lamination; arrow indicates processing direction, with spheres packed randomly. (c) Opaline film with improved sphere packing; arrow indicates shear direction [24].
2. 1.2 Concept of the optical switch: (a) Schematic representation of optical switch device in its undeformed (OFF) and (b) deformed (ON) configurations, respectively. Schematic diagram of the optical switch, indicating all the relevant dimensions. Source: López Jiménez et al. 2016 [25]. Reproduced with permission of Elsevier.
3. 1.3 Top view FESEM images of (a) PS latex films and (b) PS latex/GO films. (c) Schematic representation of the prepared samples. PS latex spheres at room temperature after drying (bottom panel) leaves disordered spheres stuck to the Parafilm. PS latex spheres after stretching; the arrow indicates the strain direction, with spheres packed ordered. Schematic illustration (top panel) of macroscopic deformation of a graphene sheet on a stretched silicone substrate; first wrinkles form on PS latex spheres, and then unfold as the substrate is strained.
4. 1.4 (a) Electrical resistance to initial resistance values variations of PS latex/GO/Parafilm coupled with silicone substrate through the stretching and (b) stretching cycles from λ = 1 to λ _max = 1.05, 1.2, 1.4, 1.5, 1.6, 1.65, 1.7, and 1.8, and then returned to a relaxed state (λ _max → 1).
5. 1.5 (a) FESEM image of the strained PS latex/GO/Parafilm coating. (b) Transmittance of unstrained (red line) and strained (blue line) PS latex/GO/Parafilm coating. Optical micrographs of PS latex/GO/Parafilm sample in (c) stretched and (d) unstretched state, respectively. The arrow indicates the strain direction.
6. 1.6 (a) Optical micrographs and schematic side/top view of GNP platelets embedded in Parafilm matrix in stretched state (i.e. the arrows indicate the strain direction). The initial side/top view shows an interconnected electrical path of GNPs; GNPs then separate during stretching, thus raising the electrical resistance of the sheet. (b) Schematic representation of stretch mechanism before the stretch at λ = 1, during the stretch at different stretching ratios, and after relaxing to an unstretched state λ = 1 of Parafilm/GNPs coupled with fluoroelastomer. (c) Electrical resistance variations to initial resistance values of Parafilm/GNPs coupled with fluoroelastomer substrate through the stretching cycles from λ = 1 to λ _max = 2, 3, or 4, and then returned to a relaxed state (λ _max = 1).
Chapter 02
1. Figure 2.1 Examples of advanced technological applications using invisible (opto)electronic devices fabricated with transparent electroactive materials.
2. Figure 2.2 Bottom‐gate/top‐contact (a) and top‐gate/bottom‐contact (b) OTFT device architectures, and the passive/electroactive layers used in these devices.
3. Figure 2.3 The chemical structures of thiazole‐phenyl and thiazolothiazole‐phenyl oligomers 1, 2, and 3 functionalized with trifluoromethyl substituents at molecular termini.
4. Figure 2.4 The chemical structures of phenylene–thiophene oligomers 4, 5, and 6 functionalized with n‐hexyl substituents and 7, 8, and 9 functionalized with n‐perfluorooctyl substituents, and non‐substituted perfluoroarene–thiophene oligomers 10 and 11.
5. Figure 2.5 The chemical structures of pentacene and fused heteroacene semiconductors 12–22.
6. Figure 2.6 (a) The chemical structure of DNT–V derivatives showing the corresponding twist angles. (b) Molecular packing diagram of 15 along with transfer integrals (t (meV)) in all directions (H, head; T, tail). (c) Transfer and output curves for the solution‐crystallized 15‐based OTFTs measured by two‐(2T) or four‐terminals(4T).
7. Figure 2.7 (a) Molecular herringbone packing motif of 4a (DNTT in Figure 2.9) and the corresponding calculated transfer integrals (ts). (b) A stacking pair of 4a showing HOMO pictorial representations. Note that the chemical structures of compounds 33b, 33c, and 34 are depicted as 18, 19C ₍₁₂₎, and DATT in Figures 2.5 and 2.9.
8. Scheme 2.1 General synthetic route to 2,7‐dialkyl substituted BTBT derivatives 19C _(n).
9. Figure 2.8 (a) Schematic of the TFT device configuration using C8‐BTBT:PS blend as the semiconducting layer, PVP:HDA as the dielectric layer, and ITO as the gate electrode. Note that the chemical structures are shown at the bottom. (b) Schematic illustration of the off‐center spin‐coating process. (c) Optical transmission spectrum of the PVP:HDA/C8‐BTBT:PS film; inset shows the photographs of C8‐BTBT:PS film and the corresponding OTFTs. (d) Normalized polarized absorption spectrum of off‐center spin‐coated C8‐BTBT:PS film with the light electrical field is in radial (blue circles) or perpendicular direction (red circles). (e) Normalized polarized absorption spectrum of on‐center spin‐coated C8‐BTBT:PS film with the light electrical field is in radial (green circles) or perpendicular (pink circles) direction. Perpendicular‐polarized absorption spectrum of a metastable C8‐BTBT:PS film before/after vapor annealing with DCB (f) and after thermal annealing for 3 h at the indicated temperature (g).
10. Figure 2.9 The optical absorption spectra of DNTT/DATT thin films, and theoretical HOMO/LUMO energies for BTBT, DNTT, and DATT, respectively, calculated at the DFT B3LYP/6‐31 g(d) level.
11. Figure 2.10 Computationally (TDDFT B3LYP/6‐31(d) level of theory) predicted HOMO/LUMO energies and pictorial representations for naphthodithiophene (NDT) constitutional isomers (1a–4a) in different molecular architectures.
12. Figure 2.11 The chemical structures of naphthalene dianhydride (23) and naphthalene dicarboximide (NDI) derivatives 24–35 functionalized with various N,N′‐substituents.
13. Figure 2.12 Packing structure of 25 showing the herringbone motif. The unit cell (C‐centered monoclinic) parameters: a = 53.22 Å, b = 5.20 Å, c = 11.81 Å, β = 92.79°, and Z = 4.
14. Figure 2.13 Optical absorption and emission spectra of (a) 27 and (b) 28 in toluene.
15. Figure 2.14 Molecular structures and packing diagrams of 30 ((a) and (b)) and 31 ((c) and (d)) (cyclohexane rings and n‐hexane chains are omitted in packing diagrams for clarity).
16. Figure 2.15 Photographs of the transparent and flexible transistors based on semiconductor 32.
17. Figure 2.16 (a) Transmission optical spectrum of vapor‐deposited NDI‐8CN2 (35) thin film (50 nm) on glass. (b) Output curve for a transparent, flexible OTFT device employing a PEDOT:PSS gate, polymer dielectric, NDI‐8CN2 (35) semiconductor, and Au source/drain electrodes. (Inset shows the photograph of an array of ∼100 devices fabricated on overhead transparency film.)
18. Figure 2.17 The chemical structures and synthesis of PNDI‐TVTx copolymers with the indicated repeating units and computed lengths (determined by DFT computations).
19. Figure 2.18 The chemical structures of pyromellitic dicarboximide (PyDI) derivatives 36–39 functionalized with various fluorinated N,N′‐substituents.
20. Figure 2.19 (a) Schematic of the transistor device structure used in the study. (b) The chemical structure of PSeTPTI. (c) Schematic of the spin‐coating process yielding ultrathin semiconductor films (2–5 nm).
21. Figure 2.20 (a) Photographs and (b) transmission optical spectra of PSeTPTI films deposited on quartz substrates from different solution concentrations.
22. Figure 2.21 The chemical structures of n‐type semiconductors NDI3HU‐DTYM2 and NDI(2OD)(4tBuPh)‐DTYM2.
23. Figure 2.22 (a) Output and transfer curves of NDI3HU‐DTYM2 based top‐gate devices having a semiconductor film thickness of 6 nm. (b) Thickness dependence of mobility for NDI(2OD)(4tBuPh)‐DTYM2/Pentacene (10 nm)‐based ambipolar OTFTs and output curves of optimized transistors. (c) Photographs of NDI(2OD)(4tBuPh)‐DTYM2 films with varied thickness showing the high transparency of flexible, ultrathin (4 nm semiconductor film) transistors. (d) I_DSAT as a function of NH₃ vapor exposure for NDI(2OD)(4tBuPh)‐DTYM2‐based thin‐film and ultrathin‐film transistors.
24. Figure 2.23 (a) Schematic of the organic transparent nonvolatile memory devices fabricated on plastic substrates. (Inset shows the SEM image of gold nanoparticles adsorbed on the APTES‐coated PVP layer.) Photographs of the transparent flexible OTFTs (b) and the memory devices (c). (The substrate size is 3 × 3 cm².)
25. Figure 2.24 (a) Micrographs (captured after 7 days in vitro) of dorsal root ganglion (DRG) cultures deposited on P13 thin film. Arrowhead, neuronal cell body; arrow, neurite extension. (b) and (c) Laser scanning confocal microscopy images of the corresponding DRG cells, stained for NeuN and GAP43 neuronal markers, respectively. (d) Representative trace of the neuron firing behavior in response to current pulses of 100 ms duration for plated on PDLC laminin coated O‐CST. Dashed line indicates the resting membrane potential. (e) Locus (left) and multiple output (right) curves measured in air (dry conditions) before exposure to physiological environment. (f) Locus (left) and multiple output (right) curves measured in air (dry conditions) after 16 days of in vitro storage.
26. Figure 2.25 The synthetic route to BOPNA, and the corresponding optical absorption and emission spectra in solution (dashed line) and as thin film (solid line).
27. Figure 2.26 Output current signals as a function of time under dark and LED flash mode for transistors fabricated with BOPNA and BOPAnt. The distance between LED and the device is ∼10 cm, and the luminous flux is ∼240 lm.
Chapter 03
1. Figure 3.1 The “magic square” of OPV. In order for the technology to be successful, four elements have to be addressed: high efficiency, freedom of design and shapes for different applications, low cost suitable for industrial production, and a long lifetime for various integration purposes.
2. Figure 3.2 (a) Solar garden lamp from Konarka Technologies. Image courtesy of the Energy Campus Erlangen‐Nuremberg. (b) Architectural integration of OPV modules as appeared at the German Pavilion at EXPO Milan 2015. (c) Façade installation of organic solar modules from Heliatek. (d) Integration of OPV into a greenhouse. Image courtesy of the Energy Campus Erlangen‐Nuremberg.
3. Figure 3.3 Typical structure of a flexible organic solar cell.
4. Figure 3.4 From light absorption to photocurrent in a bulk heterojunction solar cell. (a) From a kinetic point of view, (b) simplified energy diagram (binding energies for excitons and polaron pairs are not shown). (i) Singlet exciton generation from an absorbed photon in the donor material. (ii) Exciton diffusion to the acceptor interface. (iii) Exciton dissociation by electron transfer to the electronegative acceptor molecules. (iv) Separation of the still Coulomb‐bound electron–hole pair due to electric field and material disorder. (v) Charge transport of electron resp. hole by hopping between localized states. At this state, nongeminate recombination between independently generated electrons and holes can occur. (vi) Extraction of the charges:photocurrent.
5. Figure 3.5 Typical current–voltage characteristics of an organic solar cell (P3HT:PC₆₀BM measured at the Energy Campus Nuremberg).
6. Figure 3.6 Contour plot showing the calculated energy‐conversion efficiency (contour lines and colors) versus the band gap and the LUMO level of the donor polymer according to a model described in [20]. Straight lines starting at 2.7 eV and 1.8 eV indicate HOMO levels of −5.7 eV and −4.8 eV, respectively. A schematic energy diagram of a donor PC₆₀BM system with the band gap energy (E _g) and the energy difference (DE) is also shown.
7. Figure 3.7 Chemical structures of frequently used donor and acceptor molecules: (a) PCPDTBT: poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)]; (b) P3HT: poly(3‐hexylthiophene); (c) PC₆₀BM: phenyl‐C61‐butyric acid methyl ester.
8. Figure 3.8 (a) Typical graph of transmittance (generally measured at ∼ 550 nm) plotted versus sheet resistance for thin films of nanostructured materials. Note that each curve can be divided into two regimes, the bulk regime (solid line is a fit to Equation 3.4) and the percolation regime (dashed line). (b) Plot of sheet resistance versus number of bends for CuNW films (85% transparent) and ITO on PET. Inset shows the radius of curvature before (10 mm) and after bending (2.5 mm).
9. Figure 3.9 Scheme of a sheet‐to‐sheet doctor blade.
10. Figure 3.10 Coating techniques: (a) knife coating on a roll‐to‐roll system and (b) slot‐die coating, where the coating head can be positioned at different angles.
11. Figure 3.11 Printing techniques: (a) gravure printing, (b) flexographic printing, and (c) rotary screen printing.
12. Figure 3.12 (a) Schematic organic film formation by inkjet printing; (b) inkjet‐printed solar module portrait of Alan J. Heeger (Nobel prize for discovery and development of conductive polymers) driving a digital clock.
13. Figure 3.13 Monolithical interconnection of single cells into a module; (a) cross section of the typical structure of an OPV module, with a photoactive layer (PAL) sandwiched in between two electrodes: ITO‐metal‐ITO (IMI) and Ag. The IMI and Ag electrode are divided by patterning lines (called P1 and P3 respectively). The subsequent interconnection of the single cells is achieved in the P2 region. ℓ is the length of the patterning region, whereas L is the length of the active area of a single cell; (b) shows a top‐view of the module. D is the width of the module; (c) is an electrical model of the interconnection. R _int is the interconnect resistance; R _s,top and R _s,bottom are the sheet resistances of top and bottom electrodes respectively.
Chapter 04
1. Figure 4.1 (a) Side view of a top‐gate bottom‐contacts FET. The geometrical overlap between the gate electrode and the source and drain ones gives rise to C _gs and C _gd parasitic capacitances. (b) Small‐signal AC circuit of an FET for f _t direct measurement, where the parasitic capacitance added by the external probe is highlighted. Unfortunately, the extrinsic AC current introduced by this capacitance would not be discernable from the intrinsic i _g of the device. (c) Modified measuring scheme that can be adopted to overcome the gate capacitive loading issue, where the relevant AC current signals and the forcing gate voltage modulation are indicated, together with the AC current amperometers. (d) Simulated trend of , current (black line). The red and the blue lines represent the extracted i _d and parasitic i _gd contribution to , respectively. The measurement has to be reliable for a wide enough frequency range where the capacitive component dominates over the channel current to allow an extraction of both C _gs and C _gd components.
2. Figure 4.2 Schematics for (a) transconductance, (b) C _gs , and (c) C _gd measurement. The transistor is biased in the saturation regime of operation and then a sinusoidal small signal is applied to one terminal depending on the desired parameter to be extracted from the transfer function.
3. Figure 4.3 (a) Scheme for the determination of Y‐, Z‐, or h‐parameters of an FET. Port 1 is connected to the gate terminal while port 2 is connected to the drain terminal. The FET is a black box, the behavior of which is completely described by Y‐, Z‐, or h‐parameters determined starting from port voltages V ₁ and V ₂ and port currents i ₁ and i ₂. (b) Simulated trends of |Y ₂₁|, |Y ₁₁|, and |h ₂₁| versus frequency on a log–log scale. |Y ₂₁| is constant at low frequency, where g _m ≫ ωC _gd , while it increases by 20 dB/decade at high frequency, where ωC _gd ≫ g _m holds. |Y ₁₁| increases by 20 dB/decade in the whole frequency span since it refers to a pure capacitance. As a consequence, at low frequency, |h ₂₁| decreases by 20 dB/decade and equals unity at the same frequency at which |Y ₂₁| = |Y ₁₁|, then it flattens at high frequency, reaching the C _gd/(C _gs + C _gd) value. The extracted f _t is about 9 MHz, corresponding to the adoption in the simulation of the following parameters: C _gs = C _gd = 0.1 pF, and g _m = 10 μA V⁻¹ . (c) Two‐port network schematic. The device under test is a black box, the behavior of which is completely described by S‐parameters determined starting from the power waves incident on port 1 ( a ₁ ) and port 2 ( a ₂ ) and reflected from port 1 ( b ₁ ) and port 2 ( b ₂ ).
4. Figure 4.4 (a) Device structure and (b) f _t measurement for the high‐frequency device based on C₆₀ by Kitamura et al. Reproduced with permission from [41]. (c) Device structure and f _t measurement for the rubrene single‐crystal device. Source: Uno et al. 2013 [42]. Reproduced with permission of Elsevier.
5. Figure 4.5 (a) Device structure of a 3D‐OFET. Reproduced with permission from [22]. (b) Schematic of the geometrical overlap determining the corresponding capacitance and mechanism of charge injection in such architecture. (c) Measurement of f _t of the best device in the study. Source: Reproduced with permission from [58]. Schematic views of (d) self‐aligned printing and (e) self‐aligned gate techniques by Noh et al. (f) Transition frequency measurement of printed and self‐aligned devices. Source: Noh et al. 2007 [23]. Reproduced with permission of Nature Publishing Group.
6. Figure 4.6 (a) Sketch of the high‐resolution gravure printing technique, micrograph of the realized transistors, and summary of the f _t measurement of the realized devices. Source: Reproduced with permission from [65]. (b) Focused ion beam SEM micrograph of a cross section through device realized with nano‐imprint lithography, optical micrograph of devices with the same structure (realized with photolithography) after inkjet printing of the semiconductor, and transition frequency measurement of different sets of devices (PL, photolithography; NIL, nano‐imprint lithography; GRA, gravure printing). Source: Reproduced with permission from [66].
7. Figure 4.7 (a) Sketch and optical microscopy picture of an ablated channel in a PEDOT:PSS printed line. The scale bar is 10 μm. (b) Sketch and optical microscopy picture of patterned source/drain electrodes with an interdigitated design and with a minimum L _ov ≈ 2 μm. The scale bar is 10 μm. (c) Frequency characterization of an all‐polymer device with 12 ablated channels in an interdigitated structure. Source: Reproduced with permission from [71]. (d) Schematic of the laser sintering technique and (e) electrodes realized with such process. (f) Transition frequency measurement of OFETs integrating laser‐sintered electrodes and printed semiconductor. Source: Reproduced with permission from [72].
Chapter 05
1. Figure 5.1 (a) Growth kinetics in CVD‐produced graphene on various catalysts: Case of CH₄ on Ni and Cu. Schematic diagrams of the growth mechanism of graphene via precipitation (upper) and surface‐mediated reaction (lower). (b) SEM images of as‐grown graphene films on thin (300‐nm) nickel layers and thick (1‐mm) Ni foils (inset). (c) TEM images of graphene films of different thicknesses. (d) A confocal scanning Raman image.
2. Figure 5.2 (a) Schematic of the roll‐based production of graphene films grown on a Cu foil. (b) Structure of the fabricated graphene/epoxy/PET film. (c) Photograph of the graphene/epoxy/PET roll before doping. The widths of the graphene/epoxy and base PET films are 210 and 230 mm, respectively. (d) A4 size large‐area graphene transparent conductive film. (e) Photograph of electrostatic discharging on the substrate using an electrostatic generator. Large‐area graphene films transferred onto (f) a SiO₂/Si wafer and (g) a flexible PET substrate using the CLT technique.
3. Figure 5.3 (a) Electromechanical properties of graphene‐based touch‐screen devices compared with ITO/PET electrodes under tensile strain. The inset shows the resistance change with compressive and tensile strain applied to the upper and lower graphene/PET panels, respectively. (b) An assembled graphene/PET touch panel showing outstanding flexibility. (c) A graphene‐based touch‐screen panel connected to a computer with control software. (d) Photograph of the graphene touch screen installed in a mobile phone (left) in comparison with an ITO‐based touch‐screen phone (right). (e) Schematic diagram illustrating the concept of a graphene‐based capacitive sensor. (f) Relative capacitance change (ΔC/C ₀) versus distance between sensor and finger. The inset shows the test repeated for 200 cycles. (g,h) Image of wearable capacitive touch sensor fabricated using graphene electrodes. The images below show the touch sensor monitor and the multi‐touch, spread and scroll performances. Scale bar, 2 cm.
4. Figure 5.4 (a) Schematic illustration of a hole‐injection process from a graphene anode via a self‐organized HIL with work‐function gradient (GraHIL) to the NPB layer. (b,c) Current efficiencies and luminous (power) efficiencies of OLED devices using various graphene layers (doped with HNO₃ or AuCl₃) or ITO as anode. (d) Schematic device structure of high‐efficiency graphene‐based OLEDs. (e) EQE (f) current efficiency, and (g) power efficiency versus luminance characteristics of graphene‐based OLEDs with and without TiO₂ under‐layers. The data for ITO‐based control OLEDs are also shown for comparison. The data (e–g) belong to devices containing GraHIL as low‐index hole‐injection layers and are based on glass substrates. (h) Current efficiency versus current density characteristics measured after repeated bending at radius of curvature (r _C) of 2.3 mm. Inset: the photograph of an OLED bent at r _C of 2.3 mm placed on a custom‐made cyclic bending tester. (i) The picture of an OLED with the proposed TiO₂/graphene/GraHIL electrode in operation (upper). Photograph of the proposed flexible TiO₂/graphene OLEDs in operation (lower).
5. Figure 5.5 (a) Schematic illustration of a BHJ OSC device with electrostatically doped graphene electrode. (b) Detaching the OSC device from supporting substrate (bottom, left) and attaching to target surface (bottom, right). (c) Sheet resistance change with and without electrostatic doping for different graphene layers. (d) Stability behavior of chemically doped and electrostatically doped graphene film. J–V characteristics of (e) graphene electrodes (one to six layers) without polarization and (f) electrostatically doped four‐ to six‐layer graphene electrodes along with ITO. (g) Efficiency (triangle) and current density (square). Filled symbols represent unpolarized whereas opened represent polarized characteristics. (h) Photograph of OSC device mounted on rollable machine for rolling test. (i) Variations in J–V characteristics under cycling test. The J–V characteristics are measured for every 20 cycles. (j) Variation of normalized photovoltaic parameters under cycling test.
6. Figure 5.6 (a) Optical images of an array of devices on a plastic substrate. (b) Transfer and output characteristics of graphene FETs on plastic substrate. (c) Mechanical properties of ion gel gated graphene FETs fabricated on a flexible plastic substrate; normalized effective mobility (μ/μ ₀) as a function of the bending radius. (d) Images of the ion gel gated graphene FETs on PDMS substrate. (e) Transfer characteristics of graphene FETs as a function of the number of graphene layers. (f) Normalized hole/electron mobilities, current levels (maximum hole (red circle)/electron (blue triangle), and the minimum current at the Dirac voltage (black square)) and Dirac voltage of graphene FETs as a function of the stretching level. (g) 3‐D illustration of a water‐resistant flexible multifinger embedded gate FET. Lower panel of (A) shows flexible GFETs attached to the bending fixture and the change in normalized resistance and normalized mobility under different bending radii down to 0.7 mm. (h) The de‐embedded current gain with an intrinsic f _T of 25 GHz for flexible GFET. V _G is biased at the peak transconductance and V _D = 0.5 V.
7. Figure 5.7 (a) Repeated increase and decrease in normalized resistance of graphene strain sensor mounted on the finger of a wearable glove (inset) with respect to monitoring the finger motion up and down. (b) Photographs of a tactile sensor consisting of ultrathin graphene strain gauges on animal hide. (c) Pressure map measured by the tactile sensor when a gentle touch of 9 kPa was applied to the sensing area. (d) Resistance response of a GWF‐based strain sensor at successive stages of making a fist. (e) Optical images of stretchable devices mounted on palm for remote controlling a toy car. Inset of each image shows relative capacitance changes for spread (left) and grip (right) status of the hand. (f) Images of car controlled by capacitive sensor signals on palm.
8. Figure 5.8 (a) Wireless monitoring of glucose concentrations from 1 to 10 mM. (b) Frequency response of the intraocular pressure sensor on the bovine eye from 5 to 50 mmHg. (c) Photographs of the sensor transferred onto the contact lens worn by a bovine eyeball (left) and a mannequin eye (right). Scale bar, 1 cm. (d) Wireless sensing curves of glucose concentration before and after wearing contact lens on an eye of live rabbit. (e) Schematic drawings of the diabetes patch, which is composed of sweat‐control sensing and therapy (upper); Optical camera images of the diabetes patch laminated on human skin under stretching (lower). (f) Optical image of the glucose sensor. (g) Monitoring of glucose and pH changes in vitro under hyperglycemia in artificial sweat. (h) Optical image of the integrated wearable diabetes monitoring and therapy system connected to a portable electrochemical analyzer. (i) Optical image of the GP‐hybrid electrochemical device array on the human skin with perspiration. (j) One‐day monitoring of glucose concentrations in the sweat and blood of a human. (k) Comparison of the average glucose concentrations with commercial glucose assay data (j) before and after correction using the measured pH. (l) Optical image of the heater integrated with the microneedles, which is laminated on the skin near the abdomen of the db/db mouse.
9. Figure 5.9 (a) Spacer‐incorporated 1L graphene is integrated with PET/graphene (top electrode) to fabricate the GTNG. (b) Adjustability of graphene with the crumpled substrate is shown. (c) Output voltage from GTNGs with various numbers of graphene layers under a vertical compressive force of 1 kgf (1 kgf = 9.80665 N). The inset shows a captured image of three LED arrays that are simultaneously lit up by the power output generated from the GTNG. (d) Schematic illustration of the conformal TENGs formed on human skin. The conformal TENGs generated the electrical power by contact with fabrics. (e) Short‐circuit current and open‐circuit voltage of the conformal TENGs with various surface states. (f) Photograph of the conformal TENGs attached on the palm. (g) Optical images of self‐powered contact sensors with contact to different numbers of fingers (top) and corresponding raw data (bottom).
Chapter 06
1. Figure 6.1 The process steps involved in the formulation of GRM inks and application in devices.
2. Figure 6.2 Schematic of the wire‐wound rod coating process.
3. Figure 6.3Figure 6.3 Schematic of the spray‐coating process of a 2D‐crystal‐based ink, deposited through the air onto the substrate by a spray gun.
4. Figure 6.4 Ink transfer by screen printing.
5. Figure 6.5 An illustration of the flexo offset printing technique in a four‐roller configuration with a fountain roller that fills the anilox roller.
6. Figure 6.6 (a) The direct gravure process where the gravure roll and web are in intimate contact; (b) offset gravure printing.
7. Figure 6.7 Schematic showing typical gravure cells. (a) Pyramidal, (b) quadrangular, (c) continuous trihelical, (d) laser engraved. A cross section through each of the cells along the line of engraving is also shown.
8. Figure 6.8 Different relationships between shear stress and shear rate for Newtonian and non‐Newtonian systems leading to pseudoplastic, dilatant, and plastic behavior.
9. Figure 6.9 Pseudoplastic behavior of two different material systems: dispersion of platelets and polymer chains.
10. Figure 6.10 Schematic of a drop sitting on a rigid substrate where the contact angle is indicated by the three surface tensions ( , , ).
11. Figure 6.11 Schematic of the microfluidization process.
12. Figure 6.12 Newtonian and non‐Newtonian flow behaviors of functional inks. Inset: Flow and viscosity curves for a Newtonian liquid.
13. Figure 6.13 Particle's Einstein coefficient, as a function of particle orientation at different aspect ratios, .
14. Figure 6.14 (a) Demonstration of screen printing of the graphene ink; (b) capacitive touch‐pad design printed on paper, (c) with a line resolution of 100 m.
15. Figure 6.15 as a function of thickness ( ) in (a) linear and (b) logarithmic scale for inkjet printed graphene ink on various substrates (HMDS‐coated, ‐plasma‐treated, and pristine Si/ substrates.
16. Figure 6.16 Optical micrograph of graphene inkjet printed drops on various substrates. Scale is 20 m. SEM micrograph of graphene inkjet printed pattern.
17. Figure 6.17 FET heterostructure of graphene/h‐BN on PET (a) and textile (b). Optical microscopy (dark field) of an integrated circuit demonstrating an all inkjet printed complementary graphene inverter as shown in the schematic.
Chapter 07
1. Figure 7.1 Flexible graphene‐based smartphone produced by Chongqing Graphene Tech. Co., Ltd.
2. Figure 7.2 Graphene applications and corresponding resistance ranges.
3. Figure 7.3 Schematic presentation of rapid thermal chemical vapor deposition (RT‐CVD) synthesis and production processes of graphene films and graphene‐based capacitive touch screens.
4. Figure 7.4 Schematic presentation of a full roll‐to‐roll (R2R) production of silver nanowire–graphene hybrid flexible transparent electrodes.
5. Figure 7.5 (a) A 3D‐AFM and (b) an SEM image of CVD‐grown graphene film simply supported on PET substrate. The corresponding wrinkling network along with the isolated graphene “islands” is clearly distinguished. (c) (right) A schematic graph explaining the proposed stress transfer mechanism.
6. Figure 7.6 Schematic representation of an omni‐directionally stretchable and transparent multilayered graphene electrode supported on a textured elastomeric substrate.
7. Figure 7.7 A prototype touch panel display, manufactured by Bluestone Global Tech (New York, USA), consisting of two layers of CVD graphene embedded into PET films, is employed on a smart phone.
Chapter 08
1. Figure 8.1 Samsung Galaxy Note Edge, introduced in 2013, the first product to use a flexible AMOLED display.
2. Figure 8.2 Teardown of the Samsung Galaxy S6 Edge, showing the flexible AMOLED display after peeling it from the curved front glass.
3. Figure 8.3 Teardown of the Apple Watch, showing the very narrow region outside the active pixel area of the flexible AMOLED display.
4. Figure 8.4 LG's 18‐in. flexible AMOLED display with bending radius of 30 mm.
5. Figure 8.5 Structure of a generic double‐heterostructure OLED.
6. Figure 8.6 Lifetime effects in an OLED.
7. Figure 8.7 (a) PMOLED and (b) AMOLED display architectures, with four PMOLED pixels shown, but only one AMOLED pixel for simplicity.
8. Figure 8.8 RGB polysilicon 2T subpixels in a commercial AMOLED display. P1 is the pixel switch, and the drive transistor is implemented using two TFTs in parallel, P2a and P2b.
9. Figure 8.9 LTPS internally compensated 6 T pixels used in Samsung Galaxy smartphones.
10. Figure 8.10 LG AMOLED displays use n‐channel oxide TFTs in a pixel that adds only one additional TFT to the simple 2T pixel, with external compensation.
11. Figure 8.11 In the LLO process, after display processing is complete, irradiation by an excimer laser is used to delaminate the polymer film from the glass substrate, yielding a flexible AMOLED display.
12. Figure 8.12 A multilayer TFE coating using an alternating inorganic/organic stack. The inorganic layers provide the impermeability while the organic layers cause any pinholes or microcracks in the inorganic layers to be spatially decoupled, so that the diffusion path for permeating molecules is very long.
13. Figure 8.13 Bending a sheet of material produces tensile stress on the outside of the bend and compressive stress on the inside, with a stress‐free neutral plane within the sheet.
Chapter 09
1. Figure 9.1 Ragone plot (W kg⁻¹ vs Wh kg⁻¹) of conventional energy storage systems.
2. Figure 9.2 Schematic illustration of the working principles of an LIB. During discharge, lithium ions diffuse from the anode into the cathode. The reverse process occurs during charge.
3. Figure 9.3 Build‐up of a cylindrical 18650 battery with (a) schematic drawing [34] (edited), (b) computed tomography cross section of a commercial 18650 battery, and (c) image of a cathode/separator/anode unit.
4. Figure 9.4 (a) Schematic drawing of a flexible LIB based on graphene paper [46]. (b) Photograph of graphene paper prepared by vacuum filtration of graphene dispersion and SEM image of the cross section of graphene paper.
5. Figure 9.5 Schematic of structural models of graphene/metal oxide composites: (a) Anchored model: nano‐sized oxide particles anchored on graphene surfaces; (b) wrapped model: metal oxide particles wrapped by graphene; (c) encapsulated model: oxide particles encapsulated in graphene; (d) sandwich‐like model: metal oxide particles are squeezed between two graphene layers creating a sandwich‐like structure; (e) layered model: alternating layers of metal oxide nanoparticles and graphene; (f) mixed model: graphene and metal oxide particles mechanically mixed with graphene forming a conductive networking among the metal oxide particles. Red: metal oxide particles; blue: graphene sheets.
6. Figure 9.6 Different thin‐film design concepts: (a) stack‐type cell architecture. (b) Coplanar‐type cell architecture.
7. Figure 9.7 Schematic illustration of 3D interdigitated microbattery architecture fabricated on (a) gold current collector by printing of (b) Li₄Ti₅O₁₂ LTO and (c) LiFePO₄ (LFP) inks through 30 µm nozzles, (d) packaged, (e) SEM image of printed and annealed 16‐layer interdigitated electrodes, and (f) areal capacity of full cell composed of eight‐layer interdigitated electrodes.
8. Figure 9.8 Electrochemical properties of the cable battery with hollow anode compared to a device with non‐hollow anode. (a) Images of the cable batteries with hollow/non‐hollow design. (b) First charge/discharge profiles of the cable batteries. (c) Photograph of a prototype cable battery with 25 cm length powering an LED screen. (d) Discharge characteristics with variations in bending strain every 20 min with 0.1 C discharge current.
9. Figure 9.9 Images of an embedded battery. (a) Schematic illustration of a completed device, in a state of stretching and bending. (b) Layout of various layers in the battery structure. (c) Illustration of serpentine‐shaped interconnects. (d) Optical images of cathode electrode pads and interconnects before/after transfer printing on silicone elastomer. (e) Optical images of anode electrode pads and interconnects before/after transfer printing on silicone elastomer.
Chapter 10
1. Figure 10.1 Flexible bioelectronic device and organic materials most widely used in the versatile flexible bioelectronic platform.
2. Figure 10.2 (a) Schematic structure of the flexible ion‐sensitive OFET sensor. (b) Current responses of the flexible ion sensor to different pH levels. (c) Normalized current response to the addition of TNB solutions with concentrations down to 100 ppb. Inset: Photo of flexible TNB sensor. (d) Normalized current response to different levels of cysteine solutions. Inset: Current change for the devices fabricated on PET and silicon substrates, respectively.
3. Figure 10.3 (a) Channel current as a function of drain voltage under different levels of glucose solutions. Inset: Picture of flexible glucose sensor. (b) Normalized current response of OECT sensor to different lactate concentrations. Inset: Picture of flexible lactate sensor. (c) Schematic diagram of an OECT integrated with a flexible microfluidic system for highly sensitive DNA sensing application. (d) Transfer curves of an OECT measured at different bending status. Inset: Output characteristics of the device. (e) Gate voltage shifts of OECT DNA sensor as a function of the concentrations of the target DNA in PBS solutions. Conventional passive hybridization (in blue) and pulse‐enhanced hybridization (in red) methods were used correspondingly. The inset shows the applied electric field pulse used to enhance the hybridization of DNA.
4. Figure 10.4 (a) Photographs of the transparent and flexible organic electrodes device. (b) Recordings from 25 PEDOT:PSS array electrodes and 10 silicon probe electrodes, from superficial to deeper layers in the cortex parts.
5. Figure 10.5 (a) Photograph of a fabric transistor device. (b) Dynamic electrical performance of the fabric transistor‐based multiplexer. (c) Photograph of fabric manually woven with pristine and PEDOT‐S stained Bombyx mori silk threads. (d) Transient characteristics of channel current as a function of time when gate voltage is switched between 0 and 1.2 V.

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