Bioinspired Transparent Laminated Composite Film for Flexible Green

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A Bio-inspired Transparent Laminated Composite Film for Flexible Green Optoelectronics Daewon Lee, Young-Woo Lim, Hyeon-Gyun Im, Seonju Jeong, Sangyoon Ji, Yongho Kim, Gwang-Mun Choi, Jang-Ung Park, Jung-Yong Lee, Jungho Jin, and Byeong-Soo Bae ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b03126 • Publication Date (Web): 28 Jun 2017 Downloaded from http://pubs.acs.org on June 28, 2017

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Materials Technology Center

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A Bio-inspired Transparent Laminated Composite Film for Flexible Green Optoelectronics Daewon Lee,†‡⊥ Young-Woo Lim,†‡ Hyeon-Gyun Im,†‡ Seonju Jeong,§ Sangyoon Ji,∥‡ Yong Ho Kim,†‡ Gwang-Mun Choi,†‡ Jang-Ung Park,∥‡ Jung-Yong Lee,§ Jungho Jin,*¶ Byeong-Soo Bae*†‡ †

Department of Materials Science and Engineering, Korea Advanced Institute of Science and

Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea ‡

Wearable Platform Materials Technology Center, Korea Advanced Institute of Science and

Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea §

Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea

Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea ∥School

of Materials Science and Engineering, Wearable Electronics Research Group, Ulsan

National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Uljugun, Ulsan 44919, Republic of Korea ¶

School of Materials Science and Engineering, University of Ulsan, 93 Daehak-ro, Nam-gu,

Ulsan 44610, Republic of Korea

1 ACS Paragon Plus Environment

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KEYWORDS Chitin, Nanofiber, Transparent substrate, Perovskite solar cell, Touch screen panel, Green optoelectronics

ABSTRACT

Herein, we report a new version of bio-inspired chitin nanofiber transparent laminated composite film (HCLaminate) made of the siloxane hybrid materials (hybrimers) reinforced with chitin nanofibers (ChNF), which mimics the nanofiber-matrix structure of hierarchical biocomposites. Our HCLaminate is produced via vacuum bag compressing and subsequent UV-curing of the matrix resin-impregnated ChNF transparent paper (ChNF paper). It is worthwhile to note that this new type of ChNF based transparent substrate film retains the strengths of the original ChNF paper and compensates for the ChNF paper’s drawbacks as a flexible transparent substrate. As a results, compared to high-performance synthetic plastic films such as polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene naphthalate (PEN), and polyimide (PI), our HCLaminate is characterized to exhibit extremely smooth surface topography, outstanding optical clarity, high elastic modulus, and high dimensional stability etc. To prove our HCLaminate as a substrate film, we use it to fabricate flexible perovskite solar cells and a touch screen panel. As far as we know, this work first demonstrates flexible optoelectronics such as flexible perovskite solar cells and touch screen panel, actually fabricated on a composite film made of ChNF. Given its desirable macroscopic properties, we envision our HCLaminate being utilized as a transparent substrate film for flexible green optoelectronics.



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INTRODUCTION

The marvelous mechanical properties of the exo- and/or endo-skeleton of some marine creatures are attributed to the complex hierarchical structures of the skeletons, which invokes inspirations for designing new composite materials.1-3 The stiffness of arthropod exoskeleton,4 fracture toughness of nacre,5 and hardness of squid beak6 are good examples. As the hierarchical complexity increases, the brilliant properties of such biostructures stem from the arrangement and interactions of the individual building blocks, not from each constituent on its own. For these marine creatures, particularly, the ingenious hierarchical assembly of chitin nanofibers in a proteinaceous matrix plays a critical role for the remarkable performance of their skeletons.4-8 The nanofiber-matrix composite structure of these biological composites can serve as the design principle for the creation of novel manmade composite materials exhibiting some unprecedented properties by combining both biogenic and synthetic materials.9-11 Herein, we report a bio-inspired laminated composite film consisting of biogenic chitin nanofibers and a synthetic siloxane hybrid material as the matrix; we use this material as a transparent substrate film to fabricate flexible green optoelectronics (Figure 1).12-15

As a natural polysaccharide, chitin [poly-β-(1,4)-N-acetyl-D-glucosamine] is the 2nd abundant structural biopolymer on earth (Figure 1a) and is the main structural component of a number of marine creatures, such as exoskeleton of arthropods, mollusk shells, and endoskeleton of cephalopods.16 In these biocomposites, chitin exists as crystalline nanofibers17-18 (3-5 nm in diameter) in which the chitin macromolecules are tightly held by myriad hydrogen bonds, which are responsible for its mechanical stiffness.8 In the nanofibermatrix structure of hierarchical biocomposites listed above, therefore, chitin nanofibers 3 ACS Paragon Plus Environment

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function as a reinforcement of the proteinaceous matrix.19 Furthermore, in addition to excellent mechanical properties, the significant property of chitin nanofibers is superior optical transparency achieved by the nano-fibrillation of fibrous building blocks.20-23 Taking inspiration from nature, accordingly, chitin nanofibers have been utilized as reinforcement agents to create optically transparent composite films which emulate the nanofiber-matrix structure of biological composites.24-27 In particular, Ifuku et al. reported optically transparent chitin nanofibers/acrylic matrix resin composite films.10, 28-30 They obtained these composite films from UV-curing of the acrylic matrix resin-impregnated chitin nanofiber transparent papers (ChNF papers). Compared to such conventional crosslinked polymers obtained by the photoradical polymerization of acrylates, the siloxane hybrid materials (hybrimers), which are synthesized via the photocationic polymerization of siloxane epoxide/oxetane blends, exhibit better thermal stability, chemical stability, and processability. These properties are attributed to presence of living characters and lower oxygen sensitivity.31 With those enhanced properties, the hybrimers also show a high level of optical transparency.32 Based on these preceding researches, we report a novel chitin nanofiber transparent laminated composite film made of the hybrimer reinforced with chitin nanofibers (HCLaminate), which mimics the nanofiber-matrix structure of hierarchical biocomposites. The HCLaminate is prepared by vacuum bag compressing and subsequent UV-curing of the matrix resin-impregnated ChNF paper; a UV-curable matrix resin consists of siloxane epoxide/oxetane blends. The intimate assembly of the hybrimer and chitin nanofibers maintains the advantages and compensates for the disadvantages of the original ChNF paper as a flexible transparent substrate. As a consequence, our bio-inspired laminated composite film exhibits outstanding properties, including flexibility, smooth surface topography, 4 ACS Paragon Plus Environment


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chemical stability, thermal stability, optical transparency, mechanical robustness, and dimensional stability. Given these desirable properties, the HCLaminate can be the promising candidate for the flexible green optoelectronics substrate. We use our HCLaminate to demonstrate the fabrication of both flexible perovskite solar cells and touch screen panel, and, as far as we know, this work presents the first demonstration of flexible optoelectronics fabricated using the composite film made of ChNF. RESULTS AND DISCUSSION Figure 1a and 1b display the starting materials for the preparation of the ChNF paper and the matrix resin, which serve as nanofiber and matrix component building blocks of the HCLaminate, respectively. As the preceding step for the fabrication process of the HCLaminate, the 40 µm-thick ChNF paper is prepared via a centrifugal casting of a 2.4% (w/v) squid-pen β-chitin/hexafluoroisopropanol (HFIP) alcogel (20 ml).20 This alcogel is obtained from a homogeneous 0.4% (w/v) β-chitin/HFIP solution (120 ml) through evaporation of HFIP at ambient condition (Figure 1a). Because HFIP breaks intermolecular hydrogen bonds, leading to dissolution of ChNF, the evaporation of HFIP results in the regeneration of hydrogen bonds between adjacent chitin molecules. This evaporation induces the self-assembly of crystalline ChNF.31 From crystal structure analysis using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR), the inter-sheet diffraction peak and absorption spectrum for the ChNF paper, which are in between both αand β-polymorphs, indicate that the resultant ChNF paper is composed of α-and β-chitin crystals (dashed lines, Figure S2c and S2d).20, 31 These results suggest that the β-chitin to αchitin transformation occurs during the fabrication process of our ChNF paper.33 It should be noted that this crystalline phase transition between different chitin allomorphs is the result of the thermodynamic stability of α-chitin.9 The UV-curable matrix resin is comprised of 5 ACS Paragon Plus Environment

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cycloaliphatic epoxy oligosiloxane (CAEO)/bis-[1-ethyl(3-oxetanyl)]methyl ether (DOX) blends (Figure 1b). As illustrated in Figure S1, a sol-gel reaction between 2-(3,4epoxycyclohexyl)ethyltrimethoxysilane (ECTS) and diphenylsilanediol (DPSD) is used to prepare the CAEO.34 Following the preparation of the ChNF paper and the matrix resin, the HCLaminate is fabricated according to the steps illustrated in Figure 1c: (I and II) the matrix resinimpregnated ChNF paper is placed between glass plates and subsequently compressed in a vacuum bag compressing instrument; (III) in order to cure the matrix resin, the sample is irradiated under UV-light (Figure S2a and S2b); (IV) finally, the transparent HCLaminate of 60 µm thickness is obtained by separating both glass plates (Figure 1d). The scanning electron microscopy (SEM) images in Figure 1e and S3a show the cross-sectional structure of the HCLaminate, in which the ChNF paper is laminated between two layers of the hybrimer. Upon further investigation using energy dispersive X-ray spectrometry (EDS), the homogeneous distribution of Si in the ChNF paper, even in the central region, indicates the infiltration of the matrix resin into the ChNF paper (Figure 1e and S3b). Furthermore, this result suggests that chitin nanofibers are encrusted with the hybrimer while the matrix resin is cured, and the hybrimer can be reinforced by such monolithically embedded chitin nanofibers. As a candidate for the flexible green optoelectronics substrate, the HCLaminate is flexible enough to be bent over a cylindrical mandrel of 3.2 mm diameter without any cracks (Figure 1f). As presented in Figure 2a and S4a, the atomic force microscopy (AFM) image obtained from the ChNF paper displays the ultrafine chitin nanofibers (ca. 3 nm in diameter), which are the building blocks of the ChNF paper. Despite the nano-sized building blocks, however, the root-mean-square surface roughness (Rrms) of the ChNF paper is 2.65 nm 6 ACS Paragon Plus Environment


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because of the fibrous nature.35-36 Compared to the ChNF paper, the HCLaminate has the Rrms value of 0.37 nm, which is attributed to the layers of the hybrimer covering the ChNF paper (Figure 1e, S3a, 2b, and S4b). Note that the Rrms value of the HCLaminate is much smaller than that of conventional plastic substrates for flexible optoelectronics, including polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene naphthalate (PEN), and polyimide (PI) (Figure S5 and Table S1). This extremely smooth surface topography enables the HCLaminate to fabricate flexible devices on its surface without any additional planarization steps. In addition, the layers of the hybrimer not only improve the surface smoothness, but also serve as barriers of the ChNF paper to chemicals.37 The ChNF paper becomes crumpled after soaking in deionized (DI) water, in contrast to the HCLaminate, which shows no dimensional change (Figure 2d and 2e). Furthermore, the HCLaminate clearly demonstrates its solution stability in a variety of solvents, including ethanol (EtOH), isopropanol (IPA), and acetone (Figure 2f and 2g). This result indicates that the chemical stability of the hybrimer imparts better manufacturing capability to the HCLaminate.38 Figure 2c displays the thermogravimetric analysis (TGA) profile of the hybrimer, the HCLaminate, and the ChNF paper, and their 5% weight loss temperature (Td5%) values are 370, 289, and 236 ˚C, respectively. The onset of significant thermal degradation of the HCLaminate is observed at 255 ˚C, in comparison with that of the ChNF paper which is determined at 170 ˚C. Note that TGA curve of the HCLaminate exhibits a bimodal decomposition ascribed to the decomposition of both ChNF paper and hybrimer (Figure S6). Furthermore, in order to determine the maximum process temperature for the HCLaminate, we conduct isothermal TGA on the HCLaminate at 150 ˚C, 200 ˚C, and 250 ˚C for 5 h. As shown in Figure S7, our HCLaminate shows noticeable weight loss (i.e., thermal degradation) after thermal aging at 7 ACS Paragon Plus Environment

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200 ˚C and 250 ˚C for 5 h. However, at 150 ˚C, there is no obvious thermal degradation during the isothermal TGA. This hybrimer-assisted thermal stability39-40 of the HCLaminate permits the fabrication of high-temperature processed electronic devices on our HCLaminate. Optical transparency of our HCLaminate is assessed by ultraviolet-visible spectroscopy (UV-Vis). The total transmittance spectra of the ChNF paper, the HCLaminate, and the hybrimer are shown in Figure 3a. The ChNF paper and the hybrimer inherently exhibit superior optical transmittance (~91%) in the entire visible spectrum, and both have similar refractive indices of ca. 1.54 at 633 nm; which minimize the light scattering from the interface.41 Therefore, the HCLaminate shows an outstanding optical transmittance of 90.9% at 550 nm with a limited transmission haze, which is comparable to that of the ChNF paper and the hybrimer (Table S2). In the wavelength of UVA light (315-400 nm), however, the presence of UV-absorbable phenolic groups in the hybrimer results in slightly reduced transmittance of the HCLaminate (Figure S2a). It is also notable that conventional plastic substrates present either lower optical transmittance or higher transmission haze compared to our HCLaminate (Figure 3a and Table S2). The reinforcement effect of chitin nanofibers on the hybrimer is investigated by using tensile test, thermo-mechanical analysis (TMA), and dynamic-mechanical analysis (DMA). Chitin nanofibers are promising candidates for the reinforcing element because of its excellent mechanical properties originated from the hydrogen-bond-driven crystal structure.8, 42

In Figure 3b, the HCLaminate has higher elastic modulus than that of the ChNF paper and

the hybrimer; note that the elastic modulus of the HCLaminate (6.2 GPa) is the highest value among the tensile-tested samples (Figure 3b and Table S3). These results confirm that chitin nanofibers effectively improve the mechanical properties of the hybrimer. In combination with the crystal structure stabilized by strong hydrogen bonds between chitin nanofibers, a 8 ACS Paragon Plus Environment


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morphology of randomly entangled chitin nanofibers restricts its thermal relaxation motions (Figure 2a and S4a).20, 43 Accordingly, the thermo-mechanical properties including coefficient of thermal expansion (CTE), storage modulus (E´), and glass transition temperature (Tg) of the hybrimer also can be enhanced by the chitin nanofiber reinforcement. As presented in TMA curves of the hybrimer, the HCLaminate, and the ChNF paper, the incorporation of chitin nanofibers leads to the reduction in the thermal expansion of the hybrimer (Figure 3c). While the CTE of the hybrimer is 126 ppm K-1, the HCLaminate exhibits the extremely decreased CTE of 22 ppm K-1, which is slightly higher than that of the ChNF paper (18 ppm K-1) and PI (17 ppm K-1). Moreover, this CTE of our HCLaminate is the lowest value among commercial plastic films except PI (Figure 3c and Table S4). It should be emphasized that no noticeable glass-transition behavior is detected during the overall TMA test on the HCLaminate, whereas PEN and PET show clear glass-transition behavior at their Tg. Upon further investigation using DMA, these results can be elucidated. Ogura et al. concluded that chitin doesn’t exhibit obvious glass-transition behavior prior to its thermal decomposition because of the randomly entangled morphology of crystalline chitin nanofibers.44-45 Even though the hybrimer shows the lowest level of E’ with a weak and broad glass-transition behavior, chitin nanofibers improve the E’ and suppress such glass transition of the hybrimer. As shown in Figure 3d, therefore, the ChNF paper and HCLaminate possess the highest E’ values with tiny increase of the tan δ, in contrast to conventional plastic substrates except PI, which exhibit low E’ and an obvious tan δ peak around their Tg. Given its low CTE without Tg, our HCLaminate can sustain its original dimensions when it is subjected to the high-temperature processing. As a proof-of-concept, we demonstrate both flexible perovskite solar cells and touch screen panel using our HCLaminate as a substrate film (Figure 4). Figure 4a provides the 9 ACS Paragon Plus Environment

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device structure of the flexible perovskite solar cells fabricated on an indium zinc oxide (IZO)/HCLaminate (Figure S8), and also a reference device is fabricated on an indium tin oxide (ITO)/PET substrate. From the current density-voltage (J-V) curves, the solar cells on the IZO/HCLaminate exhibit a power conversion efficiency (PCE, η) of 12.52% with a short current density (Jsc) of 17.41 mA cm-2, an open circuit voltage (Voc) of 0.98 V, and a fill factor (FF) of 0.74 (Figure 4b); note that the performance of the device on the IZO/HCLaminate is higher than that of the reference device showing a PCE of 11.68% (Table S5). Furthermore, a bending test on the flexible perovskite solar cells on the IZO/HCLaminate and the ITO/PET confirms that the mechanical durability of the flexible device on the IZO/HCLaminate is better than that of the reference (Figure S9). This mechanical durability of the flexible solar cells on the IZO/HCLaminate originates from the mechanical robustness of the HCLaminate (Figure 3). In addition, the device structure of the fabricated touch screen panel is schematically depicted in Figure 4c. The silver nanowires (AgNWs)-coated HCLaminate serves as both top and bottom substrates (Figure S10), along with photoresist dot spacers and Au interconnects. Figure 4d and Movie S1 display the stable operation of the fabricated touch screen panel device; it is amenable to write characters on its surface. CONCLUSION In summary, we introduced a bio-inspired chitin nanofiber transparent laminated composite film made of the hybrimer reinforced with chitin nanofibers (HCLaminate), which emulated the nanofiber-matrix structure of biological composite materials. The HCLaminate was obtained from vacuum bag compressing and subsequent UV-curing of the matrix resinimpregnated ChNF paper. The ingenious hierarchical assembly between the hybrimer and chitin nanofibers allowed the new material to retain the strength of the original ChNF paper 10 ACS Paragon Plus Environment


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and compensated for its weakness as a flexible substrate film. Consequently, our HCLaminate showed the outstanding properties, including flexibility, extremely smooth surface topography (Rrms = 0.37 nm), chemical stability, thermal stability (Td5% = 289 ˚C), optical transparency (~91% at 550 nm), elastic modulus of 6.2 GPa, CTE of 22 ppm K-1 without Tg. In order to prove its possibility as a flexible transparent substrate film, we fabricated both flexible perovskite solar cells and touch screen panel using our HCLaminate. The flexible perovskite solar cells on the HCLaminate showed higher performance compared to the reference device on PET, and the touch screen panel fabricated using the HCLaminate exhibited stable operation. Given its advantageous macroscopic properties, we envision our HCLaminate being utilized as a transparent substrate film for flexible green optoelectronics. EXPERIMENTAL SECTION Materials: β-chitin extracted from squid pen,46 hexafluoroisopropanol (HFIP) (Halocarbon,

USA),

2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane

(ECTS),

diphenylsilanediol (DPSD) (Shin-Etsu, Japan), bis-[1-ethyl(3-oxetanyl)]methyl ether (DOX) (Toagosei, Japan), barium hydroxide monohydrate, triarylsulfonium hexafluoroantimonate salts, prawn shell α-chitin, trichloro(octadecyl)silane (OTS), lead (II) iodide (PbI2), dimethyl sulfoxide (DMSO), toluene anhydrous, chlorobenzene anhydrous (Sigma-Aldrich, USA), chloroform (Samchun Pure Chemicals, Korea), poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) (H.C. Starck, Germany), methylammonium iodide (CH3NH3I) (1-material, Canada), γ-butyrolactone (GBL) (TCI, Japan), [6,6]-phenyl-C61butyric acid methyl ester (PC60BM) (Nano-C, USA), silver nanowires (AgNWs) (Nanopyxis, Korea), and SU-8 photoresist (MicroChem, USA) were used without further purification. Fabrication of ChNF paper via centrifugal casting: β-chitin powder was dissolved in HFIP to prepare the 0.4% (w/v) β-chitin/HFIP solution. Undissolved impurities in the 11 ACS Paragon Plus Environment

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chitin/HFIP solution were filtered using a syringe filter to obtain the homogeneous chitin/HFIP solution. A 120 ml of homogeneous chitin/HFIP solution (0.4% w/v) was poured into a rectangular plastic container, and then this solution-containing container was covered with an aluminum foil. To prepare the 20 ml of chitin/HFIP alcogel (2.4% w/v), the covered plastic container was placed in a fume hood for 3 days. The resultant alcogel-containing container was centrifugal-casted using a centrifuge Combi-514R (Hanil Science, Korea) at the optimized rotation speed (2100 rpm), time (3 h), and temperature (20 °C). As the calendering process for the as-casted ChNF paper, it was placed between OTS-treated glasses and compressed in a vacuum hot press instrument. Preparation of matrix resin and HCLaminate: A sol–gel reaction between ECTS and DPSD was used to synthesize the CAEO. ECTS and DPSD were blended according to Si/phenyl molar ratio of 1:1.2 in a two-neck flask with a condenser and a stirrer. Then, 1 mol% of barium hydroxide monohydrate catalyst was added to the mixture. Reaction was performed at 80 °C for 6 h. After the reaction, residual solvent and H2O were removed by vacuum pumping at 80 °C. After evaporation, clear and viscous CAEO was obtained. The CAEO was then mixed with 50 wt% of DOX and 2 wt% of triarylsulfonium hexamonoantimonate photocatalyst to prepare the matrix resin. The matrix resin-impregnated ChNF paper was placed between OTS-treated glasses and compressed in a vacuum bag compressing instrument for 1 min. After UV-curing of the sample for 8 min, the HCLaminate was acquired after removal of the glass plates. Characterizations of HCLaminate: The SEM images were collected from a Nova 230 (FEI, USA). FT-IR and XRD spectra were collected using a FTIR 460 plus (JASCO, Japan) and a D/Max-2500 (Rigaku, Japan), respectively. Phase and topographic AFM images were obtained using a Dimension 3100 (Veeco, USA). Optical transparency was evaluated by both total and parallel transmittance spectra recorded with an UV 3101PC (Shimadzu, Japan) and 12 ACS Paragon Plus Environment


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an UV 2550 (Shimadzu, Japan), respectively. The stress-strain curves were measured based on the ASTM-D882-12 standard with an AGS-X (Shimadzu, Japan) at rate of 0.1 mm/min. Tensile test was performed five times on rectangular samples with a size of 6 × 50 mm. TGA, TMA, and DMA profiles were obtained from a TGA Q50 (TA Instruments, USA), a TMA/SS 6100 (Seiko Instruments, Japan), and a DMA 2980 (TA Instruments, USA), respectively, with a temperature ramp rate of 5 °C min− 1 (in N2 atmosphere). Fabrication and characterization of flexible perovskite solar cells: As a transparent electrode, IZO (160 nm) was deposited on the HCLaminate by RF sputtering (RF power = 120 W) in a vacuum (5 × 10−3 Torr) for 15 min. Fabricated flexible perovskite solar cells had the device structure of PEDOT:PSS (40 nm) / perovskite (270 nm) / PC60BM (20 nm) / Ag (150 nm). Spin-coating of PEDOT:PSS onto the IZO/HCLaminate substrate was performed at rotation speed of 4000 rpm for 30 s and then the sample was dried at 140 °C for 15 min. Perovskite (CH3NH3PbI2) solution was obtained by dissolving CH3NH3I and PbI2 according to a molar ratio of 1:1 in a blend of GBL:DMSO (7:3 v/v) at 70 °C for 12 h. The perovskite solution was consecutively spin-coated onto the as-coated PEDOT:PSS on the IZO/HCLaminate by a three-step processes at 500, 1000, and 3000 rpm for 5, 10, and 40 s, respectively. Through the third coating step, a toluene droplet of ~70 µl was dropped onto the prepared perovskite layer, and then the specimen was immediately annealed at 100 °C for 10 min. The 1 wt% PC60BM/chlorobenzene solution was spin-coated on the perovskite layer at 3000 rpm for 45 s. Ag layer was deposited on the shadow mask covered PC60BM layer by thermal evaporation in a vacuum (10-7 Torr). A reference device was fabricated on the ITO (75 nm) / PET substrate. The J-V curves of the fabricated flexible solar cells were collected in the range of 1.0 to -0.2 V by a solar simulator K201 LAB55 (McScience, Korea) under irradiance of 100 mW cm-2 from a 150 W Xe short-arc lamp filtered by an air mass 1.5 G filter. Calibration of light intensity was performed by using a Si reference cell K801S-K302 13 ACS Paragon Plus Environment

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(McScience, Korea). The illuminated area was clearly defined by attaching an aperture mask of 8.75 mm2 onto the device. Fabrication of touch screen panel: To prepare the transparent electrodes of substrate layers, the AgNWs dispersed in distilled water were spin-coated onto the HCLaminate. After coating the electrodes, the SU-8 photoresist was spin-coated at rotation speed of 3000 rpm for 30 s on the AgNWs-coated HCLaminate (bottom substrate) and photolithographically patterned to form dot spacers (diameter = 100 µm and distance between spacers = 4 mm). Deposition of Au interconnects (50 nm) were performed by using thermal evaporation in a vacuum (10-6 Torr) on the AgNWs-coated HCLaminates (bottom and top substrates), which were covered by a shadow mask. The top and bottom substrates were assembled and connected to IC board (Touch Display, Korea) and desktop computer.



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Figure 1. (a) A digital photograph of 0.4% (w/v) β-chitin/HFIP solution and chemical formula for chitin. (b) A digital photograph showing the matrix resin and chemical structures of CAEO and DOX, which constitute the matrix resin. (c) Schematic illustration of the fabrication procedure of HCLaminate. (d) A digital photograph of the transparent HCLaminate (scale bar = 2 cm). (e) An overlapped SEM-EDS Si mapping image of the HCLaminate (scale bar = 10 µm). (f) A digital photograph showing mandrel bend test of the HCLaminate (this test is conducted based on ASTM D522/D522M-13 standard).


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Figure 2. Phase AFM images obtained from (a) ChNF paper and (b) HCLaminate, showing the enhancement in surface smoothness (scale bars = 500 nm). (c) TGA curves of Hybrimer (red), HCLaminate (blue), and ChNF paper (green) with a temperature ramp rate of 5 °C min. -1

(in N2 atmosphere). Inset: magnified TGA curves. (d-e) Digital photographs displaying (d)

ChNF paper and (e) HCLaminate before and after soaking in a DI water (scale bars = 5 mm). (f-g) Digital photographs of HCLaminate (f) before and (g) after soaking in EtOH, IPA, and acetone (scale bars = 5 mm).



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Figure 3. (a) Total transmittance spectra recorded from ChNF paper (green), HCLaminate (blue), PET (yellow), Hybrimer (red), PES (brown), PEN (gray), and PI (black). (b) Elastic moduli for Hybrimer (red), ChNF paper (green), HCLaminate (blue), PET (yellow), PES (brown), PEN (gray), and PI (black). (c-d) TMA and DMA curves obtained from ChNF paper (green), HCLaminate (blue), PI (black), PET (yellow), PEN (gray), PES (brown), and Hybrimer (red), respectively.


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Figure 4. (a) The device structure of the flexible perovskite solar cells. (b) J-V characteristics of the flexible perovskite solar cells fabricated on IZO/HCLaminate (blue) and ITO/PET (yellow) (the reference device). Inset: a digital photograph and photovoltaic parameters of the flexible perovskite solar cells on HCLaminate. (c) The structure of the fabricated touch screen panel device. (d) A digital photograph for the touch screen panel device fabricated using HCLaminate. Inset: a digital photograph showing the operation of the fabricated touch screen panel. The written characters are “Chitin”.



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ASSOCIATED CONTENT

Supporting Information. The following files are available free of charge. Reaction mechanisms, FT-IR and XRD spectra, additional cross-sectional SEM and SEMEDS Si mapping images, additional AFM images, derivative weight loss profile, isothermal TGA results, total transmittance spectra for the IZO-deposited HCLaminate, bending test results, a digital photograph, SEM image, and total transmittance spectra for the AgNWscoated HCLaminate, and summary tables of Rrms, optical properties, elastic moduli, CTE, and photovoltaic parameters (PDF) Stable operation of the fabricated touch screen panel device (AVI) AUTHOR INFORMATION

Corresponding Authors *E-mail: [email protected] *E-mail: [email protected]

Present Address ⊥Carbon

Resources Institute, Korea Research Institute of Chemical Technology (KRICT),

141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea

Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Wearable Platform Materials Technology Center (WMC) funded by the National Research Foundation of Korea (NRF) Grant of the Korean 19 ACS Paragon Plus Environment

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Government (MSIP) (NRF-2016R1A5A1009926), a grant from the Korea Evaluation Institute of Industrial Technology (10051337), the National Research Foundation of Korea (NRF) (NRF-2014R1A1A1038415), KDRC support program for the development of future devices technology for display industry (10052105), and the Ministry of Trade Industry & Energy (MOTIE) (10065101). REFERENCES (1) Campbell, N. A.; Reece, J. B.; Urry, L. A.; Cain, M. L.; Wasserman, S. A.; Minorsky, P. V.; Jackson, R. B. Biology. 8th ed.; Benjamin Cummings: San Francisco, United States of America, 2008. (2) Studart, A. R. Towards High-Performance Bioinspired Composites. Adv. Mater. 2012, 24, 5024-5044. (3) Munch, E.; Launey, M. E.; Alsem, D. H.; Saiz, E.; Tomsia, A. P.; Ritchie, R. O. Tough, Bio-Inspired Hybrid Materials. Science 2008, 332, 1516-1520. (4) Raabe, D.; Sachs, C.; Romano, P. The Crustacean Exoskeleton as An Example of A Structurally and Mechanically Graded Biological Nanocomposite Material. Acta Mater.

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Bioinspired Transparent Laminated Composite Film for Flexible Green

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