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Tailorable and Wearable Textile Devices for Solar Energy Harvesting and Simultaneous Storage Zhisheng Chai,†,∥ Nannan Zhang,‡,∥ Peng Sun,† Yi Huang,‡ Chuanxi Zhao,† Hong Jin Fan,§ Xing Fan,*,‡ and Wenjie Mai*,†,⊥ †

Siyuan laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, Department of Physics and ⊥Guangdong Provincial Key Laboratory of Optical Fiber Sensing and Communications, Jinan University, Guangzhou, Guangdong 510632, China ‡ College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China § School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore S Supporting Information *

ABSTRACT: The pursuit of harmonic combination of technology and fashion intrinsically points to the development of smart garments. Herein, we present an all-solid tailorable energy textile possessing integrated function of simultaneous solar energy harvesting and storage, and we call it tailorable textile device. Our technique makes it possible to tailor the multifunctional textile into any designed shape without impairing its performance and produce stylish smart energy garments for wearable selfpowering system with enhanced user experience and more room for fashion design. The “threads” (fiber electrodes) featuring tailorability and knittability can be large-scale fabricated and then woven into energy textiles. The fiber supercapacitor with merits of tailorability, ultrafast charging capability, and ultrahigh bending-resistance is used as the energy storage module, while an all-solid dye-sensitized solar cell textile is used as the solar energy harvesting module. Our textile sample can be fully charged to 1.2 V in 17 s by self-harvesting solar energy and fully discharged in 78 s at a discharge current density of 0.1 mA. KEYWORDS: textile, tailorable, energy harvesting, energy storage, smart garment

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spinning, weaving, tailoring, and sewing. The fabrication of dual-functional (energy harvesting and storage) wearable energy textiles will go through similar processes but with more challenges ahead. Tailorability is one of the obstacles, but it has always been neglected. The energy units (fiber/textile) for smart garments should be capable of being cut into arbitrary length/shapes to meet versatile integration demand. Hence, tailorability is an essential property not only for fiber being woven into textile but also for textile being designed into clothes with different styles and sizes. Furthermore, wearable energy units inevitably suffer from some mechanical failures. The performance of the tailorable energy textile could be restored by cutting out the damaged part and reconnecting the intact part, a delicate sewing process.19,20

ioneering products ranging from bendable smart phones/watches and biomedical skinlike devices indicate that the era of wearable smart electronics has arrived.1 Several attempts have been made to fabricate wearable energy devices combined with a growing demand for lightweight and flexible energy systems.2−4 The key obstacle individual energyharvesting devices face is the intermittent nature of renewable energy.5 Meanwhile, energy storage devices have to be frequently recharged by external power sources.6−8 Recently, considerable attention has been drawn to the fabrication of integrated energy systems for simultaneous energy harvesting and storage.9−12 Such self-charging power systems can overcome the intrinsic drawback of conventional energy harvesting and storage devices. Notably, fiber-shaped energy devices, which can be woven into clothes, have appeared and quickly attracted extensive research interest.13,14 Although integrated fiber energy devices with coaxial15 or coelectrode models16−18 have been developed, weaving them into textiles is still a challenge. From cotton in the fields to a garment in the store, there are a series of complex processes involved: © 2016 American Chemical Society

Received: August 5, 2016 Accepted: September 9, 2016 Published: October 5, 2016 9201

DOI: 10.1021/acsnano.6b05293 ACS Nano 2016, 10, 9201−9207

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Scheme 1. Schematic of the Composition and Structure (“Thread to Cloth”) of the Integrated Energy Textile for Future Smart Garmentsa

Key: (a) The “threads” (fiber supercapacitor (FSC) or DSSC photoanode) can be large-scale fabricated and tailored into different segments. (b) Textile energy device produced through the processes of weaving, tailoring, and sewing in which FSC and DSSC are integrated. (c) The prospect of wearing future smart energy garment to power small electronics.

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Figure 1. TiN nanowire based FSC electrode: (a) detailed synthesis process of TiN NWs on Ti wire; (b) panoramic view SEM image of the TiN/Ti wire and the cross-sectional view SEM image of TiN NWs; (c−e) electrochemical properties (CV curves, galvanostatic charge/ discharge curves, and Nyquist plot) of the TiN/Ti wire with length of 2 cm.

As the most competent candidate for wearable energy storage device, fiber supercapacitors (FSCs) have been intensively studied owing to their high flexibility, tailorability, and knittability.21−25 Pseudocapacitive TiN nanomaterials show great promise as excellent electrode materials in supercapacitors because of their remarkable electrical conductivity (3125− 55000 S cm−1) and high specific capacitance.26−28 Although there has been some research on TiN nanomaterials for planar supercapacitors, TiN-based fiber or textile devices have not been reported yet. On the other hand, solar power is a renewable energy resource that is widely available and inexhaustible. Hence, a photovoltaic cell would be most suitable for wearable energy harvesting devices in consideration of its portability and mobility.29−31 Herein, we present an all-solid tailorable energy textile that integrates solar energy harvesting and storage, as shown in Scheme 1. The TiN nanowire (NW) based symmetric FSC with tailorability, ultrafast charging, and ultrahigh bending

resistance is designed as the energy storage module in the resulting energy textile. Large-scale production of this kind of FSC is easy to realize, and then it can be tailored into different lengths for weaving into textile. With regard to the solar energy harvesting module, we have successfully fabricated an all-solid dye-sensitized solar cell (DSSC) textile by interlacing the fibershaped photoanodes (used as flying shuttle) and counter electrodes (CEs). Scheme 1a shows that the fiber-shaped photoanode coated with solid-state electrolyte is also tailorable, the same as FSCs. Our work demonstrates a general and efficient way to fabricate various wearable and tailorable energy textile devices.

RESULTS AND DISCUSSION The fabrication process of wearable dual-functional energy textile, as shown in Scheme 1, can be described as “thread to cloth”. First, the fiber electrode/device with high flexibility and tailorability is fabricated. Then, strings of fiber electrodes/ 9202

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Figure 2. Solid-state FSC device: (a) schematic of the structure of TiN nanowire based FSC; (b, c) CV curves of the 4 cm long FSC at scan rates from 0.1 to 50 V s−1; (d) cycle performance at a current of 0.05 mA of the FSC (inset shows a blue LED lighted by three series connected FSCs); (e) capacitance retention under bent for 2000 times (from 0° to 360° for each cycle) and CV curves of the first and 2000th cycle (inset); (f) demonstration of the tailorability of the FSC.

of H2Ti2O5·H2O NWs and TiN NWs can be found in SEM images. The top-view SEM image of H2Ti2O5·H2O NWs (80− 100 nm in diameter) shows a well-aligned and uniform 1D NWs film (Figure S3a). After H2Ti2O5·H2O to was converted to TiN (Figure S3b), the average diameter of NWs remained unchanged, but the surface became rougher. Figure 1b shows the SEM image of the TiN/Ti wire (∼250 μm in diameter). It reveals that TiN NWs (∼10 μm in length) grow along a radial direction around the Ti wire compactly and uniformly. TEM analysis is carried out to further characterize the nanostructure of TiN NWs. Porous TiN NWs are exhibited in Figure S3c,d. The 1D porous structure can simultaneously provide a fast electron transport channel and large surface area, which will lead to excellent electrochemical performance such as fast charge/discharge rate and high volumetric capacitance. The first three diffraction rings in the selected area electron diffraction (SAED) pattern correspond to (111), (200), and (220) facets of the TiN phase, revealing the polycrystalline structure (inset in Figure S3c). A high-resolution TEM (HRTEM) image (inset in Figure S3d) shows the interplanar distances of d(111) = 0.24 nm and d(200) = 0.21 nm, respectively, and the interplanar angle of 55° between the (111) facet and (200) facet, which are in agreement with the TiN phase.32 Scanning and transmission electron microscope (STEM) images of single TiN NW and the corresponding energy

devices are woven with cotton yarns using an industrial weaving loom with flying shuttle to produce the energy textile with predesigned patterns (Figure S1). Because of the electric series connection, the FSCs module can be charged to several volts, enabling wide commercial application. As shown in Scheme 1b, a typical integrated solar energy harvesting and storage textile is fabricated by weaving the FSC textile and DSSC textile side by side. It is worth noting that the textile is also tailorable since every “thread” (FSC, fiber-shaped DSSC photoanode and CE) is tailorable. Finally, for practical application, the textile can be tailored and sewn to obtain wearable energy clothing with solar energy harvesting and storage features, as shown in Scheme 1c. The TiN NWs array with superior electrochemical performance is used as the active material in FSCs. In consideration of the poor cycling stability of TiN arising from the irreversible oxidation, an ultrathin amorphous carbon shell is coated onto the surface of TiN NWs. The detailed synthesis process of electrodes is schematically illustrated in Figure 1a. First, the Ti wire undergoes an alkali hydrothermal treatment and a further ion-exchange process to obtain H2Ti2O5·H2O NWs. Afterward, the TiN NWs are obtained via a nitridation process. Finally, a glucose-assisted hydrothermal deposition and subsequent carbonization method are used to coat the carbon shell on TiN NWs. XRD and XPS results validate the formation of TiN NWs (Supporting Discussion S1 and Figure S2). The morphologies 9203

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Figure 3. DSSC textile: (a) schematic of the interlaced structure of photoanode and CE; (b) cross-sectional view SEM image of the ZnOnanorod based photoanode; (c, d) output performances of the DSSC textile with strings connected in series and parallel, respectively; (e−g) performance stability tests of the DSSC textile with different bending angle and bent times; (h) demonstration of the tailorability of the DSSC textile.

capacitance (Table S1). Subsequently, the relationship of capacitance retention and scan rate is calculated to investigate the rate capability of the FSC (Figure S5b). At scan rates of 1 and 10 V s−1, it still achieves 68% and 37% capacitance retention, respectively, compared to that at the scan rate of 0.1 V s−1. To further explore the mechanism of the fast-charging ability, a series of contribution calculations on capacitive and diffusion part are carried out (Supporting Discussion S2 and Figure S6). As shown in Figure 2d, after experiencing 5000 cycles of GCD test at a current of 0.05 mA, the TiN FSC device maintains ∼87.5% in capacitance, exhibiting excellent stability. Noticeably, if the TiN NWs have not been coated with the carbon shell, the capacitance will decrease quickly during charge/discharge cycling (Figure S4e). For weaving into wearable energy storage textile, the FSCs must operate stably while undergoing bending and twisting/ wrapping. CV curves of the TiN FSC at different bending angles are displayed in Figure S7a, and no obvious capacitance decay is observed. After bending 2000 cycles (from 0° to 360°, Figure 2e), the TiN FSC maintained ∼98% of its original capacitance, demonstrating excellent bendability and stability. Furthermore, the FSC can be wrapped around a glass rod (shown in Scheme 1a and Figure S7b) and remains unchanged in capacitance, which further demonstrates the special feature of flexibility. For practical application, the TiN FSC should be mass produced readily and conveniently. A 20 cm long TiN FSC is fabricated (Figure S8), and the CV measurement is carried out to compare the performance of 4 and 20 cm long FSCs. An almost liner enhancement in capacitance vs length can be seen from Figure S8a,b (∼4.8 times at 1 V s−1 and ∼4.7 times at 0.1 V s−1), which verifies the feasibility and reliability of mass production. To confirm the application potential of the TiN FSC as energy storage device, three FSCs are connected in series to power a blue LED (inset in Figure 2d). To investigate the tailorability of the TiN FSC, a 4 cm long FSC is separated

dispersive X-ray spectrometry (EDS) mapping images further confirm the composition and structure (Figure S3e). As mentioned above, TiN can be easily electrochemically oxidized to TiO2 in the presence of water or oxygen. Hence, an ultrathin carbon shell is coated onto the surface of TiN NWs as a protecting layer.27 Figure S4a−c shows SEM and TEM images of TiN NWs coated with carbon shell (∼5 nm in thickness). The carbon shell can serve as an active capacitive material; hence, a slight elevation in capacitance after coating the carbon shell can be seen from cyclic voltammetry (CV) curves in Figure S4d. The enhancement in electrochemical stability is investigated below in detail. To simplify, in the following, unless expressly stated, all of the TiN NWs employed in the performance test are presumed to be coated with carbon shell by default. Figure 1e shows the CV curves of the TiN/Ti electrode in a three-electrode system at different scan rates from 0.01 to 0.1 V s−1, indicating good capacitance behavior. Galvanostatic charge/discharge (GCD) curves at different current density are shown in Figure 1f, which again reveal the good capacitive property of the TiN/Ti electrode. Moreover, the Nyquist plot displayed in Figure 1g demonstrates low series resistance of the electrode. The solid-state FSC device (4 cm in length) is fabricated into a symmetric structure by assembling two TiN/Ti electrodes, while the KOH/PVA gel is simultaneously used as electrolyte and separator (Figure 2a). CV curves at different scan rates in Figure 2b,c exhibit good capacitance responses even at a very high scan rate of 50 V s−1. Also, GCD curves (Figure S5a) show nearly symmetric triangles with a Coulombic efficiency of over 85%, indicating good reversibility and smooth charge delivery between two electrodes. The specific capacitance of 0.36 mF cm−1 (2.28 mF cm−2 and 0.37 F cm−3) can be calculated from the CV curve at the scan rate of 0.1 V s−1. In contrast with some previous works, our TiN FSC presents a rather good 9204

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Figure 4. Integrated energy textile: (a) photographs showing the tailorability of the textile cloth which integrates DSSC and FSCs functions; (b) equivalent circuit; (c) light-charge and galvanostatic discharge performance.

for more than 2 months without capsulation, as shown in Figure S9. It is worth noting that the photoanodes or CEs are tailorable; hence, the DSSC textile is also tailorable. As demonstrated in Figure 3h, there is a DSSC textile with Isc of 0.41 mA and Voc of 0.41 V. After this textile is cut into halves, each part maintains almost half of the original Isc (∼0.21 mA) and full value of the original Voc (0.41 V). Moreover, when the two detached textiles are connected in parallel, the photoelectric performance can be fully recovered. When the two detached textiles are connected in series, Voc of 0.94 V is achieved. The above results manifest that the tailorable DSSC textile holds interesting features to harvest solar energy, and if further integrated with energy storage function, the much sought-after tailorable energy textile can be achieved. As shown in Figure 4a and Figure S10, by introducing more cotton yarns, FSCs and DSSCs are woven together side by side to forming the light-charging energy textile (DSSC−FSC unit). Thus, our “thread to cloth” routine has been accomplished. More weaving patterns are viable since the energy textile starts from 1D “threads” (FSCs, fiber-shaped photoanodes and CEs), which are flexible and tailorable. The tailorability of the whole textile is demonstrated in Figure 4a. The charging and discharging performance of the integrated energy textile is studied. The equivalent circuit of a light-charging system is shown in Figure 4b. Nine strings of photoanodes with a length of 4 cm are divided into three groups and connected in series. For each group, three strings of photoanodes are connected in parallel. As expected, the Voc can rise up to ∼1.2 V, the appropriate voltage to charge the TiN FSC. Therefore, two parallel connected TiN FSCs (4 cm in length) are used as the energy storage module in this system. When exposed to light, the DSSC module generates electric energy and the supercapacitors module can store it. As shown in Figure S11, under different light intensities, the FSC module can be fully charged at different rates. Under one sun illumination (100 mW cm−2), the FSC module can be charged by the DSSCs module to 1.2 V in 17 s (Figure 4c). The discharge process is realized by a galvanostatic method with the constant current density. To fully discharge the FSC module, it takes 78 s at a current of 0.1 mA, 40 s at 0.2 mA, and 20 s at 0.4 mA. It is worth noting that the performance parameters in this DSSC−FSC unit are tunable: the charging rate can be adjusted by increasing the length of photoanodes in DSSC module (Figure S12), further demonstrating the extensive applicability of our energy textile, which can meet various energy requirements of wearable electronics.

into two parts of equal length, i.e., 2 cm (Figure 2f). Parts 1 and 2 each present almost half of the capacitance of the original 4 cm long one, revealing that the tailoring process hardly affects the performance of the TiN FSC. In addition, two segments can be reconnected in series or parallel. According to CV curves, the FSCs in parallel demonstrates only slight falloffs in capacitance, indicating that these FSCs can be restored via a simple parallel connection even if they are cut off or broken. In the solar energy harvesting module, the interlaced fibershaped photoanodes and CEs are woven through a shuttleflying process (photoanodes as the flying shuttle, as shown in Figure 3a and Figure S1). ZnO NWs are grown on Mn-coated polymer wire and subsequently sensitized by dye N719. After coating a hole-transfer layer (CuI), the fiber-shaped photoanode is obtained (as shown in the SEM image of Figure 3b). The CE is the Cu coated polymer wire or cotton yarn. To investigate the output performance of the textile-type DSSC module, strings of photoanodes are connected in series or parallel, and the photocurrent−voltage (I−V) characters of them have been recorded. As shown in Figure 3c, the opencircuit voltage (Voc) of the DSSC textile connected in series increases linearly with the number of the photoanode strings, while the short-circuit current (Isc) remains unchanged. For six strings of photoanodes with a length of ∼2 cm, Isc of 0.28 mA and Voc of 2.6 V are achieved. Meanwhile, the Isc of the DSSC textile connected in parallel also increases linearly with the number of the photoanode strings, while the Voc is unchanged (Figure 3d). For six strings of photoanodes with lengths of ∼2 cm, Isc of 2 mA and Voc of 0.4 V are achieved. These results demonstrate the applicability and adaptability of DSSC textiles for matching the power requirement of various electronics or energy storage devices. The DSSC textile shows excellent flexibility and bending tolerance, as demonstrated by photocurrent density-voltage (J−V) character testing produced at different bending states. The device performance is rather stable at different bending angles from 0° to 120° (Figure 3e,f). The mechanic stability is also quite good; even if the bending cycles increase up to 100, there is no degradation in performance (Jsc, Voc, and efficiency), as shown in Figure 3g. Indeed, the power conversion efficiency of solid-electrolytebased DSSC is lower than that of the liquid-electrolyte-based one, and this is the major trade-off of the tailorable device. Moreover, the performance stability of the DSSCs with CuI solid-state electrolyte should be affirmed. As observed in the experiment, the chemical stability of the CuI-type all-solid DSSC textile is excellent. There is no obvious performance decline after the DSSC textile was stored in a dry environment 9205

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module, the photoanodes were employed as the flying shuttle and the other direction “threads” were Cu coated polymer wires or cotton yarn, as schematically shown in Figure S1. Characterization. The morphology and nanostructure of samples were characterized by field emission scanning electron microscope (FE-SEM, ZEISS ULTRA 55), transmission electron microscope (TEM, JEOL 2100F), X-ray diffraction (XRD, Rigaku) analyzer, and X-ray photoelectron spectroscope (XPS, Thermo K-alpha). The electrochemical properties of FSCs and the photoelectrical properties of DSSCs were measured on a CHI 660D electrochemical workstation. An AM 1.5 solar simulator (San-Ei, XES40, 100 mW cm−2) was used as the light source. The electrochemical impedance spectra (EIS) of FSCs were recorded using VerasSTAT 3-400 (Princeton Applied Research) at a potential amplitude of 10 mV. The single TiN electrode tests were performed in 1 M KOH solution. Saturated calomel (SCE) reference electrodes and Pt counter electrodes were used in the measurements.

In the future development of smart garments, researchers may consider not only further improving the energy conversion and storage performance of the devices but also to bringing more functionality of the textile device such as color indication and light-emitting or human physical signal monitoring capabilities.

CONCLUSION In summary, we present a single layer of energy textile possessing integrated functions of simultaneous solar energy harvesting (by ZnO-based DSSC) and storage (by TiN-based FSC), which is a perfect solution for self-powered smart garments. The TiN FSC demonstrates excellent tailorability, superior electrochemical performance (0.36 mF cm−1), great cycling stability (87.5% capacitance retention after 5000 cycles), and ultrahigh bending resistance (98% capacitance retention after bending 2000 times). A well-designed all-solid DSSC textile also exhibits superior tailorability, high power conversion efficiency (0.9%), and excellent stability (no degradation in 60 days). Our techniques make it possible to weave our different devices into a single layer of multifunctional textile in many possible patterns and tailor them into any designed shape without losing their performance. This breakthrough makes it possible to produce stylish smart energy garments with enhanced user experience and more room for fashion design.

ASSOCIATED CONTENT S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.6b05293. Additional figures, tables, and discussions (PDF)

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected].

EXPERIMENTAL SECTION Preparation of TiN/Ti Electrodes. The Ti wires (250 μm in diameter) were cleaned in ultrasonic baths of acetone and ethanol sequentially and then dried in the ambient air. As reported previously,30 the H2Ti2O5·H2O NWs on Ti wire were fabricated using an alkali hydrothermal treatment and a further ion-exchange process. Afterward, TiN NWs were obtained by annealing the asprepared H2Ti2O5·H2O NWs in ammonia atmosphere (800 °C for 1 h). A two-step process was employed to coat a thin carbon shell around the TiN NWs. Specifically, 30 mL of 0.1 M aqueous glucose solution and TiN/Ti wires were transferred into a 50 mL Teflon-lined stainless-steel autoclave. The sealed autoclave was kept in a electric oven at 180 °C for 3 h. After being cooled and washed by deionized water, the sample was annealed in nitrogen at 600 °C for 1 h. Fabrication of the Solid-State FSCs. The KOH/PVA gel electrolyte was synthesized by dissolving 6 g of PVA powder in 60 mL of 1 M KOH aqueous solution and then heating to 80 °C with continuous stirring until a transparent red gel was formed. Before assembly FSC devices, TiN/Ti wires were immersed in the KOH/ PVA gel for a few minutes. Two TiN/Ti wires were inserted into a plastic tube (0.8 mm in internal diameter) in parallel; subsequently, the gel electrolyte was injected into the tube by a syringe. The device should be retained at room temperature for several days to evaporate excess water, and after that, the plastic tube can be removed. Preparation of the DSSC Photoanode. In consideration of integration with FSCs textile, the current collector of the photoanode in DSSCs could be selected but not limited to Ti wire. For lower cost and lighter weight, Mn-coated polybutylene terephthalate wire is also applicable. On the metal or metal-coated wire, ZnO NWs is grown via a hydrothermal method (in an aqueous solution containing 0.03 M zinc acetate and 0.03 M hexamethylenetetramine at 95 °C for 10 h). After being washed with deionized water and dried at 85 °C for 4 h, the as-prepared samples were immersed in alcohol containing 0.5 M N719 and sensitized for 24 h. The CuI electrolyte was directly deposited on the sensitized photoanode using CuI/CH3CN solution at 130 °C under N2 atmosphere. Weaving Process of the Solar Energy Harvesting and Storage Textile. The solar energy harvesting module and energy storage module were both woven into plain patterns by a shuttle-flying process. In the FSC module, the FSCs were employed as the flying shuttle and the other direction “threads” were cotton yarn. In DSSC

Author Contributions

Z.S.C. and N.N.Z. contributed equally to this work and developed the concept, designed and performed experiments, analyzed data, and prepared the manuscript. P.S. performed experiments, interpreted data, and wrote the manuscript. Y.H. performed experiments and collected data. C.X.Z. contributed analysis tools. H.J.F. gave technical support and conceptual advice. X.F. and W.J.M. built constructs, supervised the project and analysis, and edited the manuscript. All authors discussed the results and commented on the manuscript at all stages. Author Contributions ∥

Z.C. and N.Z. contributed equally to this work.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS We thank Prof. Zhong Lin Wang from Georgia Tech for helpful discussions. We thank Lianhuan Du, Jiuwang Gu, and Yunfeng Zhan from Jinan University for assistance with the experiments and Jianyun Yin from Chongqing University for being a model in the photo in Scheme 1. We thank Ms. Biying Huang for her English language editing service. We acknowledge financial support from the National Natural Science Foundation of China (Grant Nos. 21376104 and 61604061) and the Natural Science Foundation of Guangdong Province, China (Grant Nos. 2014A030306010 and 2014A030310302). X.F. thanks the financial support from the Program for New Century Excellent Talents in University of China (NCET-13-0631). REFERENCES (1) Zhu, G.; Chen, J.; Zhang, T.; Jing, Q.; Wang, Z. L. Radial-Arrayed Rotary Electrification for High Performance Triboelectric Generator. Nat. Commun. 2014, 5, 3426. (2) Yang, Z.; Deng, J.; Sun, X.; Li, H.; Peng, H. Stretchable, Wearable Dye-Sensitized Solar Cells. Adv. Mater. 2014, 26, 2643−2647. 9206

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DOI: 10.1021/acsnano.6b05293 ACS Nano 2016, 10, 9201−9207