A Roll‐to‐Roll Gravure‐Printing System for Manufacturing Near‐Field Energy‐Harvesting Labels

Billions of costless near‐field communication (NFC) sensor labels per day are demanded to practically enable edge computing between smartphones and everyday objects. However, to activate the billions of NFC sensor labels daily, providing an inexpensive manufacturing method for billions of wireless energy‐harvesting labels (WeHL) per day will become a decisive issue for realizing the practical applications. Herein, a roll‐to‐roll (R2R) gravure, a typical high‐throughput additive manufacturing method, is explored to print WeHLs where six diodes and six capacitors are integrated. To meet the high‐throughput manufacturing speed (90 mm s−1) of the R2R gravure system, six different electronic inks are formulated to print the WeHLs to harvest ±10 V from the smartphone's NFC carrier. To attain a practical device yield under the given printing speed, the web tension, nip force, doctor blade angle, and overlay printing registration accuracy are well controlled and optimized to print six different layers within a high overlay printing accuracy, while printing patterns to connect two electrodes with a height difference greater than 3 μm. The fully R2R‐printed WeHLs can successfully harvest energy from the smartphone's NFC carrier with the conversion efficiency of 50%.


Introduction
[3][4] Especially, a near-field communication (NFC at 13.56 MHz) protocol to attain data from everyday objects in a short distance will be one of the key players in edge computing. [5]To efficiently utilize the NFC protocol in the edge computing, an inexpensive and flexible label-like NFC sensor device would be practical without security issues.Thus, to realize the edge computing via a smartphone, billions of NFC sensor labels per day should be operated with inexpensive and sustainable power sources.Otherwise, utilizing the NFC sensor labels will be one of the world's leading sources for causing global warming.[8] However, up to the present, no reports about the R2R gravure platform to print a wireless energy-harvesting label (WeHL) in which six diodes and six capacitors are integrated to convert the NFC carrier of the smartphone into bipolarized direct current (DC) power for operating the NFC sensor labels. [9]Although our group demonstrated the R2R-gravureprinted zinc oxide-polyaniline-based diodes, working at a customized NFC reader, it could not harvest energy from the NFC carrier of the smartphone due to its high turn-on voltage. [10]o reduce the turn-on voltage, an indium gallium zinc oxide (IGZO)-based diode, fabricated by vacuum deposition and photolithography under inert conditions, could harvest energy at 1.1 GHz carrier frequency because vacuum-deposited IGZO has the low turn-on voltage and high mobility of 10 cm 2 Vs À1 . [11]hus, IGZO-based ink was formulated to print the Schottky diode with laminated aluminum foil as a top electrode with low-work function to fabricate the WeHLs, which showed 50% efficiency at the NFC carrier of the smartphone. [10]However, the aluminum foil cannot be replaced by printed one to massproduce the WeHLs.Therefore, instead of using low-work functional metal-based ink, the Schottky contact with a printed high-work function electrode, poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate) (PEDOT:PSS), [12] was designed to convert the printed Ag bottom electrode to high-work function one by simply printing PEDOT:PSS ink on the Ag electrode so that the Schottky contact can be rendered with the printed IGZO.To complete the Schottky diode structure, carbon ink was employed to print the top electrode to render Ohmic contact on the printed IGZO layer.
Thus, to utilize the R2R gravure-printing system as a highthroughput additive manufacturing platform to fabricate the inexpensive and flexible WeHLs without hazardous byproducts, all six different electronic inks were formulated [13] to meet the practical high-throughput printing speed (90 mm s À1 ) and ink transfer to maintain designed structures: silver (Ag)-nanoparticlebased ink for bottom electrode, PEDOT:PSS ink for inducing Schottky contact to the printed IGZO layer, IGZO ink for the active layer of the diode, BaTiO 3 nanoparticle-based ink for the dielectric layer of the filter capacitor, copper (Cu) ink for the top electrode of the filter capacitor, and carbon ink for the top electrode of the diode were formulated to meet the drying time of 5 s while passing through 2 m length of drying chamber.In this study, the engraved cell structures in the gravure cylinder, web tension, nip force, doctor blade angle, and overlay printing registration accuracy (OPRA) were matched to demonstrate the R2R gravure as the sustainable high-throughput manufacturing platform [14] to mass-produce the WeHLs to harvest the bipolarized direct current (DC) power from NFC carrier of the smartphone (Figure 1a).Furthermore, we explore a way of printing patterns to connect two electrodes with a noticeable height difference and the thickness effect of PEDOT:PSS to optimize the device performance and yield (Figure 1b,c).

Results and Discussion
The viscosities of formulated six different inks as a function of shear rates were measured to maintain the consistent ink transfer at the given printing speed of the R2R gravure system. [15]n general, since a shear rate significantly influences the behavior of ink transfer in the gravure-printing unit, especially for non-Newtonian, the viscosity varies depending on the gravureprinting speed. [16]Thus, the printing speed should be matched with the ink viscosity to maintain printed devices with constant electrical characteristics.Thus, we first characterized shear-ratedependent viscosity for the formulated inks, and all six inks in this work have shown shear-thinning properties (Figure 2a,b).Since the printing speed was optimized to be 90 mm s À1 , which will be converted to a shear rate of 10 s À1 , the selected viscosities for six different inks were measured at the shear rate of 10 s À1 .Since topology and the edge waviness of the printed layer varied depending on the relationship between the viscosity at the given printing speed and the engraved gravure cell structure, [17] the engraved gravure cell structures were optimized based on the selected viscosity at the shear rate of 10 s À1 and then, confirmed the cell structures by employing them to print.All cell structures for printing six different inks without any micro-defects should have a wall thickness of 5 μm or less (Table 1).
At the given ink's viscosity and engraved cell structure, the ink is rolled over the engraved cylinder and then wiped off to remove excess ink via the doctor blade.During this process, the ink is compressed, sheared, and then transferred to flexible substrates such as poly(ethylene terephthalate) (PET) film, called the ink transfer. [18]Thus, the gravure cell structures, viscosity, surface tension, web speed, and doctor blade angle are cooperatively influencing the effective ink transfer for optimizing the topology and edge waviness of the printed patterns.As part of these efforts, we optimized the electronic ink conditions (viscosity and surface tension) and printing conditions (web speed, nip force, doctor blade angle, and drying oven temperature) for printing the rectifiers, as summarized in Table 1.
For attaining printed fine patterns for all six different inks, the doctor blade angle was set to 9°for each printing to remove the tail of the printed pattern's edge (Figure 3a).In addition, unlike the other organic vehicles, water-based PEDOT:PSS ink was challenging to get the homogenous surface using the gravure-printing method because of the high surface tension of water (72 mN m À1 at room temperature).To overcome the difficulty in printing the ultrathin film of high-quality PEDOT:PSS, polyvinyl alcohol (PVA) polymer as a binder and Triton X-100 as ionic surfactant were added into the final formulation of PEDOT:PSS ink formulation for wetting on the printed Ag electrode.
To practically print multilayers using the R2R gravure in-line printing system (Figure S1, Supporting Information), the limits of OPRA must be evaluated for the employed ink.In the previous study, we briefly explained the basic working mechanism to precisely control the OPRA for the machine direction (MD) and the transverse direction (TD) of the R2R gravure-printing system using three cameras with feedback control (Figure 3b). [7]n this study, we further expand the OPRA of the R2R gravure system to print six different inks with a wide range of ink viscosities.The basic principle of the OPRA is following: the first camera unit detected the printed registration markers on the printed film after passing through the first printing unit.Then, the second camera detected the registration markers on the gravure Table 1.Summary of the R2R gravure system as a sustainable manufacturing platform for mass producing six diodes and six capacitors as a rectifier.cylinder at the second printing unit.Based on the obtained image of both markers, the printing position at the second printing unit was calculated and controlled to minimize the registration errors by moving the gravure roll with the MD and TD.After passing the second printing unit, the third camera confirmed the OPRA at the MD and the TD.As such, using this servomechanism to control the OPRA in the R2R gravure-printing system, we maintained the OPRA of AE 25 μm at the MD and AE 50 μm at the TD under a 90 mm s À1 printing speed to print six layers with six different inks (Table 1).
Based on the OPRA (AE 25 and AE 50 μm for the MD and the TD, respectively), the WeHL was designed and printed to get stable bipolarized DC from the NFC carrier signal of a smartphone (Figure 1a).Furthermore, as vertically stacked structures are known to prevent short or leakage, [19] the R2R gravure was utilized to print this stacking structure.For utilizing the R2R gravure system with two printing units, Ag nanoparticles-based ink was employed to print bottom electrodes for diodes and filter capacitors.Then, BaTiO 3 -based ink was used to continuously print the dielectric layer for the filter capacitors.After printing the BaTiO 3 layer on the printed Ag electrode, the PET film was rewound, and the top electrodes of the filter capacitors were printed selectively on the printed dielectric layers using Cu ink.Then, formulated PEDOT:PSS ink was printed on the printed Ag electrodes to induce the Schottky contact with the IGZO layer.After printing the PEDOT:PSS layer, IGZO-based ink was printed on PEDOT:PSS layer to render the Schottky contact.Finally, carbon ink was printed as the top electrode of the IGZO layer to make lateral contact with the next diode (Figure 1b,c).To fabricate the diodes, difficulty in bridging the printed bottom Ag electrodes to the printed IGZO layers with 3 μm of the height difference should be resolved via the R2R gravure-printing method.To connect the Ag electrode and IGZO layer, the engraved cell structure and carbon ink viscosity were matched to overcome the height difference (Figure 1b,c).Thus, carbon ink with viscosity of 1,600 cP at the printing speed of 90 mm s À1 was selected with an engraved cell structure of 30 μm of depth, 185 lines, and 5 μm of wall thickness, as shown in Table 1 and Figure 1c.
Figure 4a presents the layout of the WeHL.From the optimized inks and R2R gravure-printing process, a fully R2R-printed WeHL roll (six diodes and six capacitors) was successfully obtained, as shown in Figure 4b.The optical images of the printed single WeHL are shown in Figure 4c.Observing the cross-sectional scanning electron microscope (SEM) image, the thicknesses of the R2R-gravure-printed Ag/PEDOT:PSS/IGZO/ carbon in the diode were 400 nm, 300 nm, 1.8 μm, and 2.3 μm, respectively, without any intermixing layers between printed layers (Figure 4d).Given the WeHL structure, we characterized the printed capacitor part (Ag/BaTiO 3 /Cu) by measuring the leakage current value and observed a low leakage current (below 200 pA) in our cases, sufficient to perform a filter capacitor function (Figure S2, Supporting Information).Also, studies about the frequency-dependent capacitance (Figure S3, Supporting Information) showed that the filter capacitances operated well in the range of 1 MHz.
Since the printed PEDOT:PSS layer is critical to the diode performance (Ag/PEDOT:PSS/IGZO/carbon), different thicknesses of PEDOT:PSS were printed on the Ag bottom electrode by utilizing the R2R gravure-printing process, while the other layers were fixed.Based on the thickness of the printed PEDOT:PSS layers, the diode's performance was studied using a semiconductor parameter analyzer and precision inductance, capacitance, and resistance (LCR) meter (20 Hz-1 MHz).As shown in Figure 5a, PEDOT:PSS thickness was controlled by repeating the R2R-printing process.In other words, by repeating the printing process of the PEDOT:PSS layer, we could obtain the different thicknesses of the PEDOT:PSS layer.Thickness measured by focused-ion-beam SEM (FIB-SEM) for PEDOT:PSS layers were 150, 300, 600, and 900 nm, respectively, by printing one time, two times, three times, and four times as shown in Figure 5a-d.Also, the optical topology of different thicknesses of PEDOT:PSS layer on the printed Ag bottom electrodes were observed and shown in Figure S4a-d, Supporting Information.As the printed PEDOT:PSS thickness is thicker, an iridescent image of the PEDOT:PSS layer was waned.For PEDOT:PSS layer with the thickness of 150 nm, we observed no Schottky junction due to the direct contact of Ag electrode to IGZO layer through the very thin layer of PEDOT:PSS (150 nm).However, the printed PEDOT:PSS layers with the thicknesses of 300-900 nm were shown Schottky junctions with the printed IGZO layers (Figure 5b-d).In fact, the printed PEDOT:PSS layers with more than 300 nm thickness was enough to induce the Schottky junctions by avoiding any interconnection between the printed Ag and IGZO layers.
The linear relationship between the printing number and the thickness of the printed PEDOT:PSS layer is clearly shown in Figure 6a.Although repeating the printing PEDOT:PSS layer more via R2R printing obviously induced the Schottky junctions, we found many defects on the printed IGZO surface due to the thicker layer of the PEDOT:PSS, and no more improvement of the Schottky junction after five times of PEDOT:PSS printing.The average output voltages of Ag/PEDOT:PSS/IGZO/carbonbased diodes are shown in Figure 6b with the function of the different thicknesses of the PEDOT:PSS layer.A single diode with 600 nm of PEDOT:PSS shows the highest voltage output (%2.5 V for the input voltage of 10 V peak-peak (Vp-p) at 13.56 MHz) with less variation (%1.0 V) in samples than the others.The rectification ratio (RR) as a function of applied bias for the diode was also measured to see the role of the thicknesses of the PEDOT:PSS in the diodes.[22] Figure 6c summarizes the RR values obtained from the diodes based on different thicknesses of PEDOT:PSS layer.Among those diodes, the highest value of RR was obtained for Ag/PEDOT: PSS(600 nm)/IGZO/carbon-based diode showing more than 10 2 , even higher than Ag/PEDOT:PSS(900 nm)/IGZO/carbonbased diode.Similarly, the frequency response of the different thicknesses of PEDOT:PSS-based diode has been tested with the input voltage from the function generator.It has been found that 600 nm thickness of PEDOT:PSS-based diode showed better output response (2.5-3 V for the input voltage of 10 Vp-p at 13.56 MHz) than the other cases, as shown in Figure 6d.In addition, the cutoff frequency in the Ag/PEDOT: PSS(600 nm)/IGZO/carbon-based diode can reach the 50 MHz, which can be enough for using in the near-field energy harvesting for NFC sensor labels.Among them, in the Ag/ PEDOT:PSS(300 nm)/IGZO/carbon-based diode sample, the device yield was 25%, when the printed WeHLs were tested every 0.5 m printed length for 10 m (Figure 6e). Figure 6f shows the variation of Vout for Ag/PEDOT:PSS(600 nm)/IGZO/carbonbased diode along a 10 m length (2.37 AE 0.66 V).From the start printing position (0 m), all the printed didoes have similar electrical properties.Based on our measurements for the samples, printed optimized conditions, the highest device yield (Figure 6e) of 66% was obtained from Ag/PEDOT:PSS(900 nm)/IGZO/ carbon-based diodes as shown in Video S1, Supporting Information.In contrast, the lowest device yield (<5%) was observed in the thin layer of PEDOT:PSS (150 nm)-based diodes owing to the leakage current between Ag bottom electrode and the IGZO layer (Figure 6e).
Regarding for the current-voltage (I-V ) characterization, Ag/PEDOT:PSS(600 nm)/IGZO/carbon-based diode also shows a low threshold voltage and better on-off ratio than others (Figure 7a).In contrast, the Ag/PEDOT:PSS(150 nm)/IGZO/ carbon-based diode exhibits a much higher leakage current (%60 μA at À3 V).This large reverse leakage current may be due to the lower work function of the Ag electrode or the direct connection between the Ag and IGZO layer.Therefore, the PEDOT:PSS layer should be judiciously tuned to obtain enhanced forward current and low reverse leakage current so that the high rectification could be achieved.Moreover, built-in potential (V bi ) and background carrier concentrations for all cases were calculated using a 1/C 2 -V curve from the maximum slope of the curve, as shown in Figure 7b.Indeed, the diode with the thicker PEDOT:PSS layer shows both enhanced forward current and low reverse leakage current, consequently enhancing the diode RR (Figure 7c).Here, Equation (1) was adopted to see the relationship between capacitance and voltage to calculate depleted charge concentrations per each diode (Figure 7d). [10] In Equation ( 1), q is the elementary electric charge, C is the geometrical capacitance of the diode, ε 0 is the permittivity in a vacuum, and ε s is the relative dielectric constant.N depl is the depletion region charge concentration related to the IGZO doping, and k is Boltzmann's constant.The previous cyclic voltammetry study found -4 eV of conduction and -5.6 eV of valence band energy for the IGZO layer. [10]Using equation where ϕ b is the barrier height, E C is the conduction band, and E F is the Fermi level of IGZO), [23] the barrier height of each case was estimated as 0.9-1.3eV depending on their PEDOT:PSS thicknesses.Also, the depleted charge concentration with 900 nm thickness of PEDOT:PSS layer was shown the highest value due to the high built-in potential, since N depl is directly proportional to built-in potential.Among the four different thicknesses of PEDOT:PSS-based diode samples, the PEDOT:PSS layer with the thickness of 600 nm-based diode shows a low built-in potential and low barrier height (%0.9 eV), as shown in Figure 7e.From our study, we could find the optimal thickness of PEDOT:PSS layer as 600 nm, which shows the highest output voltage (2-2.5 V, 50%) with relative high device yield (%60%) based on the printed devices along 10 m length.
Based on the R2R gravure-printed tripler type of WeHL (Figure 4a) with the 600 nm thickness of PEDOT:PSS layer, the rectified output voltage from the NFC carrier of the smartphone was shown in Figure 8a.From the NFC carrier of the smartphone, the bipolarized DC AE 10 V of output voltage was obtained from our R2R-printed WeHL with the printed antenna sample during the active state of NFC mode of the smartphone (active mode is 8 ms and pause mode is few seconds). [24]egarding for the printed antenna for testing the NFC function of the smartphone, the same R2R gravure was employed to print NFC antenna patterns on polyimide (PI) film based on the previously reported design. [25]As a result, the attained Q factor (Q = 1/R (resistance) Â p [L(inductance)/C(capacitance)]) of the printed antenna on PI film was 4.02. [21,26]Furthermore, after connecting the commercial supercapacitor (multilayer ceramic capacitor, 10 μF), DC AE 10 V of output voltage from the R2Rprinted WeHL was able to keep providing during the pause mode from the smartphone (Figure 8b).A commercial inorganic light-emitting diode (LED, 57 mW) and a commercial supercapacitor (10 μF) were mounted on R2R-printed WeHL to demonstrate the wireless power transmission concept on the PI film. [27]The photograph image in Figure 8c and Video S2, Supporting Information, show that a fully R2R-printed flexible energy-harvesting NFC label can couple a 13.56 MHz signal from the smartphone and convert it into DC voltage to turn on the LED (57 mW) successfully.At the same time, to make device more practically meaningful, output voltage was measured with a function of distance between the R2R-printed WeHL and the smartphone.For this purpose, output voltages were measured with distance from 5 to 35 mm.At 5 mm, the output voltage was 8.5 V while 35 mm distance showed 1.5 V output (Figure S5, Supporting Information).The low output voltage at 35 mm would be caused by the high resistance of the R2R-printed antenna.Thus, to improve the performance, we will adopt intense pulsed light photonic sintering in the near future.Also, toward all printed WeHL, we are planning to replace commercial supercapacitors with all R2R-printed supercapacitors by using the in-plane structure consisting of the Ag/carbon/Al-doped lithium-lanthanum-zirconated oxide with poly(methyl methacrylate) soon.

Conclusion
For the first time, the R2R gravure system was demonstrated as an additive high-throughput manufacturing platform to massproduce WeHLs by integrating six Schottky diodes, six filter capacitors.Herein, the fully R2R-printed WeHL can rectify up to 50 MHz and successfully demonstrate the wireless energy harvesting from the NFC carrier signal of the smartphone.The Schottky junction in the diode was induced by employing the printed PEDOT:PSS layer on the printed Ag electrode using the R2R gravure-printing process.After studying the function of the printed PEDOT:PSS layer, the 600 nm thickness of PEDOT: PSS-based diode with the RR of >10 2 showed the highest output (%2.5 V).However, the device yield (%66%) was higher in the 900 nm thickness of PEDOT:PSS layers than the others (00%-25% for 150 and 300 nm of PEDOT:PSS layer).In summary, the fully R2R-printed WeHL have been demonstrated to harvest energy with 50% efficiency from the NFC carrier of the smartphone and would open the way to commercialize the energy-harvesting NFC labels on a flexible substrate such as PI, polyethylene naphthalate (PEN), and PET film.Furthermore, as a proof of concept for the wireless power transmission, we successfully demonstrated wirelessly lighting an LED (57 mW) based on the WeHL under the smartphone NFC mode.Thus, an inexpensive and printed label-like NFC rectenna could be used to develop various flexible NFC sensor labels while complementing the new era of sustainable R2R-gravure-printed electronics.

Experimental Section
Material: In the first step, Ag nanoparticle-based gravure ink for printing the bottom electrode and BaTiO 3 -based gravure ink for printing the dielectric layer were formulated based on our previously reported ones. [28]The formulation of PEDOT:PSS-based high-work function ink was carried out by following our previously reported method. [10]Briefly, 3.0 mL of dimethyl sulfoxide (99.7%, Sigma Aldrich, USA) and 2 mL of isopropyl alcohol (99.9%,Duksan, Korea) were dissolved in 40 mL of PEDOT:PSS (PH-1000, Heraeus Clevios, Germany).After stirring for 4 h, 1.35 g of PVA (Mw 66000, Sigma Aldrich, USA) and 0.1 mL of Triton X-100 (Sigma Aldrich, USA) were added into this ink to meet the gravure-printing process.For the formulating the IGZO gravure ink, we followed previously reported procedure, [10] which was based on the mixture of 50 g of indium (III) nitrate hydrate (In(NO 3 ) 3 •xH 2 O, 99.9%, Sigma Aldrich, USA), 6.246 g of gallium (III) nitrate hydrate (Ga(NO 3 ) 3 •xH 2 O, 99.99%, Sigma Aldrich, USA), and zinc acetate dihydrate (Zn(CH 3 COO) 2 •2H 2 O, 98%, Sigma Aldrich, USA) with 2-methoxy ethanol (99.8%,Sigma Aldrich, USA) via hydrothermal process.At the last step, 5 wt% of PVA was added into IGZO ink to meet the final gravure ink formulation.The carbon and copper ink in this study were purchased from Dozentech (DC-14, Korea), Changsung Nanotech (ECOSIL-COP102HS, Korea), respectively.Furthermore, after mixing with diethylene glycol monoethyl ether acetate (99%, Sigma Aldrich, USA) for carbon ink and terpineol (96%, Sigma Aldrich, USA) for copper ink, we used those inks for printing the top layers of the filter capacitor and diode, respectively.A roll of the PET (AH71D, SKC, Korea) film with a thickness of 100 μm and width of 250 mm was employed as a flexible substrate in R2R gravure printing.
R2R Gravure Printing: For printing the WeHL (six diodes and six capacitors), six different electronic inks were prepared and printed on PET film via the R2R-printing system (i-PEN, Korea) under ambient conditions (24 AE 2 °C of temperature, 40 AE 5% of humidity).After the ink transferring to the film, the film was passed through a 2 m length of heating chamber (150 °C) for 5 s.In more detailed printing conditions including the inks, we discussed the results and discussion part.
Ink and Printed Device Characterization: The surface tension and viscosities of six different inks were measured using SV-10 Vibro Viscometer (A&D Co., Japan).The semiconductor analyzer (Keithley 4200, USA) and an LCR meter (E4980A, Agilent, USA) were used to measure the capacitance-voltage (C-V) and I-V characteristics of the printed

Figure 1 .
Figure 1.a) The schematic of the fully roll-to-roll (R2R) gravure-printing process for fabricating the wireless energy-harvesting label (WeHL) in which six diodes and six capacitors were integrated.Optical images of printed carbon electrodes to bridge printed indium gallium zinc oxide (IGZO) layer and printed Ag electrode with a noticeable height difference using the carbon inks with viscosity of b) 800 cp and c) 1,600 cP.

Figure 3 .
Figure 3. a) A single printing unit of the R2R gravure-printing system to control the blade angle.b) The overlay printing registration accuracy of R2R gravure-printing system.

Figure 4 .
Figure 4. a) A circuit layout of the WeHL.b) Optical image of R2R gravure-printed WeHLs on poly(ethylene terephthalate) foil.c) Optical image of detailed WeHL where six Schottky diodes and six filter capacitors were integrated.d) Cross-sectional scanning electron microscope (SEM) image of fully R2R-printed diode.

Figure 6 .
Figure 6.a) Current-voltage (I-V ) characteristic of Ag/PEDOT:PSS/IGZO/carbon-based diode with different thicknesses of PEDOT:PSS layer.b) Rectifying DC output signal on different thicknesses of PEDOT:PSS layer.c) On/off ratio characteristics on different thicknesses of PEDOT:PSS layer.d) Plot for showing the frequency dependence of Ag/PEDOT:PSS (600 nm)/carbon-based diode.e) Device yield of Ag/PEDOT:PSS/carbon-based diodes with different thicknesses of PEDOT:PSS layer.f ) The output variation of Ag/PEDOT:PSS (600 nm)/carbon-based diodes along 10 m of the printing length.

Figure 8 .
Figure 8. a) Rectified bipolarized DC power (red and blue lines) in the printed WeHL from near-field communication (NFC) carrier signal of the smartphone (black line).b) Bipolarized DC output voltage of printed WeHL from the NFC carrier signal of a smartphone after connecting commercial supercapacitors.c) Demonstration image for showing to turn on a commercial light-emitting diode under a fully printed rectifier system.