silver nanowires via layer-by-layer method for organic photovoltaic devices

Journal of Colloid and Interface Science 505 (2017) 79–86

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Fabrication of a transparent conducting electrode based on graphene/ silver nanowires via layer-by-layer method for organic photovoltaic devices B. Tugba Camic a, Faruk Oytun b, M. Hasan Aslan a, Hee Jeong Shin c, Hyosung Choi c,⇑, Fevzihan Basarir d,e,⇑ a

Department of Physics, Gebze Technical University, 41400 Gebze, Kocaeli, Turkey Department of Chemistry, Istanbul Technical University, 34469, Maslak, Istanbul, Turkey Department of Chemistry and Research Institute for Natural Sciences, Hanyang University, 04763 Seoul, South Korea d Materials Institute, TUBITAK Marmara Research Center (MRC), 41470 Gebze, Kocaeli, Turkey e Next Chemicals & Plastics, 34490, Ikitelli, Istanbul, Turkey b c

g r a p h i c a l a b s t r a c t Highly transparent and conductive graphene/Ag NWs hybrid electrode has been successfully developed by using layer-by-layer method for organic photovoltaic cells as an alternative to conventional indium tin oxide electrode.

a r t i c l e

i n f o

Article history: Received 13 March 2017 Revised 18 May 2017 Accepted 19 May 2017 Available online 22 May 2017 Keywords: Transparent conducting electrode Silver nanowire Graphene oxide Layer-by-layer deposition Organic photovoltaics

a b s t r a c t A solution-processed transparent conducting electrode was fabricated via layer-by-layer (LBL) deposition of graphene oxide (GO) and silver nanowires (Ag NWs). First, graphite was oxidized with a modified Hummer’s method to obtain negatively-charged GO sheets, and Ag NWs were functionalized with cysteamine hydrochloride to acquire positively-charged silver nanowires. Oppositely-charged GO and Ag NWs were then sequentially coated on a 3-aminopropyltriethoxysilane modified glass substrate via LBL deposition, which provided highly controllable thin films in terms of optical transmittance and sheet resistance. Next, the reduction of GO sheets was performed to improve the electrical conductivity of the multilayer films. The resulting GO/Ag NWs multilayer was characterized by a UV–Vis spectrometer, field emission scanning electron microscope (FE-SEM), optical microscope (OM) and sheet resistance using a four-point probe method. The best result was achieved with a 2-bilayer film, resulting in a sheet resistance of 6.5 X sq
1 with an optical transmittance of 78.2% at 550 nm, which values are comparable to

⇑ Corresponding authors at: TUBITAK Marmara Research Center (MRC), Materials Institute, 41470 Gebze, Kocaeli, Turkey (F. Basarir), 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, South Korea (H. Choi). E-mail addresses: [email protected] (H. Choi), [email protected] (F. Basarir). http://dx.doi.org/10.1016/j.jcis.2017.05.065 0021-9797/Ó 2017 Elsevier Inc. All rights reserved.

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those of commercial ITO electrodes. The device based on a 2-bilayer hybrid film exhibited the highest device efficiency of 1.30% among the devices with different number of graphene/Ag NW LBL depositions. Ó 2017 Elsevier Inc. All rights reserved.

1. Introduction Transparent conducting electrodes (TCEs) play an important role in organic electronic devices such as solar cells, light emitting diodes, and transistors [1,2]. Indium tin oxide (ITO) is typically used in TCEs for its superior optical and electrical characteristics. Although ITO has excellent transparency in the visible spectrum, low sheet resistance, and effective work function for injection and collection of charge carriers in organic semiconductors, its further use has been restricted because of the lack of indium resources, brittleness, and complex processing system [3]. Therefore, cheap, flexible and solution-processable ITO alternatives need to be developed for next-generation optoelectronic devices. Recently, new materials have been developed, including graphene nanosheets (GNs) [4], carbon nanotubes (CNTs) [5], conducting polymers [6], and metallic nanowires [7]. Among them, onedimensional (1D) silver nanowires (Ag NWs) and GNs have been attracting more attention because of properties alternative to conventional ITO. Generally, the sheet resistance of Ag NWs electrodes is less than 80 X sq
1 for 90% transmittance in the visible region [8]. These optoelectrical properties meet industrial requirements, however the Ag NWs electrodes have several drawbacks such as resistance [9], high surface roughness [10], and a hollow-space area between the Ag NWs [11]. The voids between neighboring nanowires create shunting and a corresponding leakage current, resulting in a high sheet resistance. The oxidation of Ag NWs also increases sheet resistance due to junction–junction resistance between nanowires [12], and haziness [13]. A combination of Ag NWs and GO is an effective method to overcome these problems. Graphene has been widely used in optoelectronic devices because of its unique properties such as high carrier mobility [14], a quantum hall effect [15], high thermal and electrical conductivity [16], large surface area [17], ease of surface modification, and excellent electrocatalytic activity [18]. Moreover, a GO layer can prevent the oxidation of Ag NWs in a graphene/Ag NWs (G/Ag NW) hybrid film because of the gas barrier property of graphene. GO laminates the Ag NWs surface by filling empty space, resulting in a low roughness. GO is also an electrical insulator because of the oxygencontaining functional groups. Alternatively, these polar groups make the GO surface hydrophilic, which leads to high dispersibility in a polar solvent, particularly in water [19]. Moreover, this property enables easy chemical modification or functionalization of the GO sheet. Chemical or thermal reduction render the GO conductive. Chemical reducing agents eliminate the oxygen containing functional groups on GO and restore sp2 carbon networks [20]. Researchers have investigated various reducing agents, including hydrazine (N2H4) [21], sodium borohydride (NaBH4) [22], lithium triethylborohydride [20], and hydrohalic acids [23]. Among these reducing agents, GO reduction by hydrazine causes a high sheet resistance, while it is not suitable for practical applications because of its high toxicity [24]. In this perspective, NaBH4 is a more effective reductant of GO by reducing the C@O species [25]. However, NaBH4 does not effectively reduce epoxy groups and carboxylic acids [26], and alcohol groups still remain after the reduction [27]. In this study, we fabricated G/Ag NWs hybrid transparent electrodes as an ITO alternative. 3- and 2-bilayer G/Ag NWs structures exhibited good electrical conductivity and optical transparency, which are comparable to those of ITO. We first prepared

positively-charged Ag NWs (Ag NWs-NH2) by grafting of cysteamine, which forms ANH2 functional groups on the Ag NWs. After the Ag NWs-NH2 were coated on the GO surface, the Ag NWs-NH2 reacted with the epoxy functional groups of GO. By the strong electrostatic interaction between GO and Ag NWs-NH2, the hybrid film was obtained using a layer by layer (LBL) coating, which is a versatile method to assemble the solution processed nanomaterial on the thin film. Furthermore, this technique makes it possible to control the thickness, transmittance, and sheet resistance. For LBL coatings of GO and amine-functionalized Ag NWs (Ag NWs-NH2), a spin-assisted assembly and dip coating method were used, respectively. Researchers have reported many methods of coating GO on the glass substrate, including spin coating, dip coating, vacuum filtration, liquid-liquid assembly, LangmuirBlodgett assembly, and a chemical vapor deposition (CVD) technique [28]. Most of these methods are difficult for obtaining homogeneous GO thin film because of the tendency to crumble. However, the spin-assisted assembly coating is a convenient and simple method for GO coating. Although many methods have been used to fabricate Ag NW thin films, including vacuum filtration [29], drop-casting [30], Meyer rod coating [31], and transferring [32] methods, dip coating is considered more convenient and powerful for self-assembly of Ag NWs-NH2 on a GO layer. Finally, the GO/Ag NWs hybrid film is reduced by NaBH4. The LBL process allows for the production of G/Ag NWs hybrid TCEs with a low sheet resistance and high optical transmittance. 2. Experimental 2.1. Materials Graphite flakes (150 lm flakes), sulfuric acid (H2SO4, 95–98%), phosphoric acid (H3PO4, 85%), potassium permanganate (KMnO4), cysteamine (HSCH2CH2NH2), sodium borohydride (NaBH4), hydrogen peroxide (H2O2, 30%), 3-aminoproplytriethoxysilane (APTES), anhydrous ethanol, methanol, and isopropyl alcohol (IPA) were purchased from Sigma–Aldrich. Silver nanowires (Ag NWs) dispersed in IPA (20 mg/ml) with an average diameter of 50 nm and length of 5–10 lm were obtained from ACS Materials. Glass slides (Menzel-Glaser, 15  15 mm2) were sonicated in acetone and ethanol for 15 min and treated with piranha solution (7:3 H2SO4/H2O2) at 90 °C for 1 h (Caution: Piranha solution is a strong oxidant and should be handled with care). The samples were then sonicated in deionized (DI) water for 5 min and dried under N2 flow. 2.2. Synthesis of GO GO was synthesized according to a modified procedure [33]. Briefly, graphite flakes (3.0 g) were added to 400 ml of a concentrated H2SO4/H3PO4 mixture (9:1 v/v) and stirred until a homogeneous suspension was obtained. Then, KMnO4 (18.0 g) was added to the mixture slowly and allowed to stir at 50 °C for 24 h. After the reaction was cooled to room temperature, the solution was poured onto ice (360 g) and stirred with a magnetic stirrer. Next, hydrogen peroxide (7 ml, 30%) was added to the solution and stirred for 4 h in an ice bath, followed by centrifuging (5000 rpm, 20 min) to remove the acid and other impurities. The final product was washed with DI water, hydrochloric acid (HCl), and ethanol sequentially, followed by drying overnight under vacuum at 50 °C.

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2.3. Preparation of amine-functionalized Ag NWs Amine-functionalized Ag NWs (Ag NWs-NH2) were synthesized according to a modified procedure [34]. First, Ag NWs (10 mg) were centrifuged to remove IPA and dispersed in 50 ml ethanol. Then, cysteamine (30 mg) was added to the Ag NWs solution followed by stirring for 24 h at room temperature. Then, the Ag NWs-NH2 were precipitated by centrifugation and the final product was dispersed in DI water. 2.4. Preparation of G/Ag NWs hybrid conducting films The LBL coating of GO and Ag NWs-NH2 was performed for preparation of TCE, which is schematically shown in Fig. 1. First, the glass substrates were functionalized by immersing in a 3% APTES solution for 3 h, followed by rinsing with excess methanol and drying under N2 flow. The substrates were then annealed at 100 °C for 1 h to enable crosslinking of the APTES molecules on the surface. The GO solution (1 mg/mL, 150 lL) was spin-coated (2500 rpm and 25 s) on the APTES modified substrate, washed with DI water vigorously, and dried at 50 °C for 30 min. Next, the substrates were dipped into the Ag NWs-NH2 dispersion (0.5 mg/ml) for 20 min, followed by rinsing with DI water and drying at 50 °C for 30 min. Multilayer films were obtained by repeating these processes. Consequently, the films were dipped in the 150 mM NaBH4 solution at room temperature for 2 h to reduce the GO and then washed with excess DI water. Finally, the films were annealed in a tube furnace at 230 °C for 30 min under an air atmosphere (see Fig. 2). 2.5. Film characterization Structural changes of the GO sheets were investigated by a Raman spectrometer (Invia, Renishaw) using a 514 nm argon ion laser in the range of 100–3200 cm
1. The surface composition of the Ag NWs-NH2 was detected by X-ray photoelectron spectrometer (XPS, K-Alpha, Thermo). Surface charges of GO and NH2-Ag NWs were determined by zeta potential analysis (Nano ZS, Malvern Instruments, UK). The surface morphology of the TCEs was analyzed by optical microscope (OM, ECLIPSE L150, Nikon), atomic

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force microscope (AFM, Bruker Dimension Icon), and field emission scanning electron microscope (FE-SEM, JEOL 63335F JSM). The sheet resistances of the TCEs were measured with a four-point probe technique (RM3000, Jandel) while the optical properties were examined using an ultraviolet visible spectrometer (UV–Vis, Lambda 750, Perkin-Elmer, USA). 2.6. Device fabrication and characterization For fabrication of the reference device, ITO-coated glass substrates were cleaned by ultrasonicating sequentially in DI water, acetone, and IPA. The following procedure was utilized for both ITO and G/Ag NWs TCE substrates. A precursor solution of vanadium oxide (vanadium (V) triisopropoxide:IPA = 1:60 [vol.%]) was spin-cast on ITO-coated or G/Ag NWs-coated glass substrates at 6000 rpm for 40 s, forming the hole transport layer. After transferring samples into the nitrogen-filled glovebox, the active layer was spin-cast on the V2O5 layer using a P3HT:PCBM solution (1:0.8 [wt. %]) dissolved in a mixed solvent of dichlorobenzene:diphenylether (97:3 [vol.%]). Without thermal annealing, an aluminum electrode with a thickness of 100 nm was deposited on the active layer via a thermal evaporator at 10
6 torr. The J-V curves of the devices were measured under AM 1.5G illumination (100 mW cm
2) and inside a nitrogen-filled glove box without encapsulation (Keithley 2401 SourceMeter). 3. Results and discussion The obtained GOs were characterized by Raman spectroscopy (Fig. 3a). The first-order G and D peaks, both arising from the vibrations of sp2 carbon, appeared at approximately 1580 cm
1 and 1350 cm
1, respectively. The G peak is due to the optical E2g phonons at the Brillouin zone center resulting from the bond stretching of sp2 carbon pairs in both rings and chains [35]. The D peak is due to the breathing modes of sp2 atoms in the rings [36]. In order to obtain positively-charged Ag NWs, the amine moiety was introduced to Ag NWs using cysteamine via a ligand exchange reaction. The thiol group of cysteamine reacts with the silver atoms on the surface of Ag NWs, which in turn led to the formation of amine-functionalized silver nanowires (Ag NWs-NH2). The XPS

Fig. 1. Schematic illustration for (a) modification process of Ag NWs with cysteamine and (b) grafting of Ag NWs-NH2 on the GO layer.

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Fig. 2. Schematic process for LBL assembly of GO and Ag NWs-NH2.

analysis was utilized for evaluating the composition of the Ag NWs after surface modification. As shown in Fig. 3b, the XPS spectra of Ag NWs-NH2 illustrated peaks at 162.3, 163.3, and 164.4 eV, which could be attributed to the S–Ag bond between cysteamine and Ag NWs, S–H bond of unreacted cysteamine, and the S–C bond of cysteamine, respectively. These results are in good agreement with previous publications [37,38]. Zeta potential measurements were performed for Ag NWs-NH2 and GO dispersions in DI water to determine the surface charges and stability. Regardless of the pH, the surface charge of GO was highly negative due to the oxygen groups (Fig. S1a). However, the best dispersion was obtained for pH 10 (
40.8 mV in) due to the protonation of the COOH groups. Additionally, the surface charge of Ag NWs-NH2 was determined as +31.2 mV (Fig. S1b). Particles with highly negative or positive zeta potentials (more than 30 mV or less than
30 mV) provide sufficient mutual repulsion to ensure a stable dispersion [39]. The results indicate that GO and Ag NWs-NH2 possessed sufficient surface charge for the stability of the dispersions. The morphology of the GO/Ag NWs films was strongly influenced by the number of GO/Ag NWs bilayers. As shown in Fig. 3 (c–e), the density of the Ag NWs on the substrate was increased with an increasing number of bilayers, indicating successful LBL deposition. It is noticeable that even 1-bilayer film resulted in a high density of nanowires (Fig. 3c). Increasing the number of bilayers led to an increase in the packing density of the nanowires and a decrease in the size of the voids (Fig. 3d and e). Macro-images of the GO/Ag NWs multilayer films with different bilayers are shown in Fig. 4a. It is clear that increasing the number of bilayers increased the concentration of the yellowish color due

to the increase in the Ag NWs density. This implies successful LBL deposition. The sample is still transparent after deposition of 3-bilayer. As shown in Fig. 4b, the optical transmittance of hybrid films decreased with increasing the number of layers. Each GO and Ag NWs layer led to a decrease in optical transmittance of approximately 2.3% and 8.6%, respectively. The transmittance values of 1-, 2- and 3-bilayer TCEs were 89.1%, 78.3% and 67.5%, respectively. These results proved that GO and Ag NWs were successfully coated. This strong bonding between the GO and Ag NWs was derived from the ionic interactions between the negatively-charged hydroxyl groups on the GO and the positively-charged protonated amine groups on the Ag NWs-NH2. Table 1 shows the sheet resistance and transmittance values of the GO/Ag NWs and G/Ag NWs hybrid films with different number of bilayers. The sheet resistances of 2- and 3-bilayer GO/Ag NWs films were 537 kO sq
1 (78.3%) and 520 kO sq
1 (67.5%), respectively. Compared to Ag NWs, GO has a lower electrical conductivity due to the rich hydrophilic oxygen-containing groups such as carbonyl, epoxide, and carboxylic acid. For this reason, when GO was introduced to the top layer of the multilayer film (TCE), the sheet resistance increased from kO sq
1 to MO sq
1 (Table 1). Upon reduction, most of the oxygen-containing groups, in particular the hydroxyl, epoxide, and carboxylic acid, were completely removed [40] and the sheet resistance of the 2- and 3-bilayer GO/Ag NWs films decreased from 537 and 520 kO sq
1 to 6.5 and 5.7 X sq
1, respectively (Table 1). We suspect that both graphene and Ag NWs network contributed to the conductivity of the hybrid film. The graphene acted as a conducting bridge between disconnected Ag NWs and linker molecules, which generated closer contact of overlapped Ag NWs. Alternatively, the Ag NWs played a role

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Fig. 3. (a) Raman spectra of GO and graphite (b) XPS S2p spectra of Ag NWs-NH2 (c) Optical microscope images of 1 layer, (d) 2 and (e) 3 layer GO/Ag NWs films.

as a conducting path in the G/Ag NWs film. Therefore, the G/Ag NWs film revealed better electrical conductivity. To date, a wide range of chemical reducing agents have been reported to eliminate oxygen-containing functional groups and restore pi-pi conjugation of GO. Among them, GO reduction by NaBH4 is simple and effective in the restoration of the graphene structure [25]. As a result, NaBH4 was employed for GO reduction in this work. The molarity of NaBH4 and reduction time are important for the efficient reduction of GO. The degree of reduction affected the sheet resistance of the reduced GO. According to literature [22], the sheet resistance was still high with 15 mM NaBH4reduced GO due to the presence of boron oxide complexes. A low sheet resistance was obtained when using 150 mM NaBH4 for GO reduction. At a low molar concentration, boron oxide complexes were formed and produced a slightly expanded interlayer distance by interacting with functional groups of GO. In contrast, at a higher concentration, functional groups of GO removed, and thus boron oxide complexes eliminated along with functional groups in GO. And higher NaBH4 concentration resulted in decreasing interlayer distance and sheet resistance. In this work, 150 mM NaBH4 was used for reduction processes and reduction was performed for a dipping time of 2 h to prevent the self-oxidation of NaBH4 in water. Finally, the sheet resistance of the 2- and 3-bilayer TCEs decreased to 6.5 O sq
1 (transmittance: 78.2%) and 4.0 O sq
1 (67.3%) after thermal annealing at 230 °C (Table 1). The annealing treatment further decreased the sheet resistance by inducing nanowire welding [41]. The G/Ag NWs-NH2 hybrid film showed lower optical

transmittance than GO/Ag NWs-NH2, suggesting a slightly higher optical absorption due to partial restoration of the p-electron system within the carbon structure after reducing the GO film [42]. The performances of TCEs in terms of transparency and sheet resistance were calculated by the figure-of-merit (FOM) equation, which is the ratio of the electrical and optical conductivity of the film, FOM ¼ Z 0 =2Rs ðT
1=2
1Þ, where Z0 is the impedance of free space [377 X], Rs is the sheet resistance of the film [X sq
1], and T is the transmittance of the film. The FOM values of 2- and 3bilayer TCEs were 218 and 214, respectively. For comparison, the FOM of ITO TCE was 297, which is calculated from its sheet resistance of 15 X sq
1 and transmittance of 85% [43]. This evaluation indicated that hybrid TCEs had comparable FOM values to that of typical ITO. Fig. 5 shows typical scanning electron microscope (SEM) images of the surface morphology of GO/Ag NWs hybrid films as a function of the number of layers. It is difficult to understand from the SEM images of GO whether it fully covers the substrate. However, a sparse network of Ag NWs in Fig. 5a illustrates that a fully covered GO layer was not obtained. Although the Ag NWs network was sparse, it created electrical conductive paths for the TCEs. However, this structure caused a high sheet resistance. The Ag NWs network became dense with increasing the number of GO layers (Fig. 5b and c). The GO sheets circumvents Ag NWs due to the flexible and stretchable properties of graphene [44]. This situation ensures a tight contact between the Ag NWs that decreased the sheet resistance of the film.

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Fig. 4. (a) Macro-images and (b) transmittance of GO/Ag NWs multilayer films.

Table 1 Sheet resistance and transmittance of hybrid TCEs.

a

TCE

T (%)

Rs (O sq
1)

Pristine GO 1-Bilayer GO/Ag NWs 2-Bilayer GO/Ag NWs 2-Bilayer G/Ag NWs 2-Bilayer G/Ag NWs (anneal.)a 3-Bilayer GO/Ag NWs 3-Bilayer G/Ag NWs 3-Bilayer G/Ag NWs (anneal.)a

97.7 89.1 78.3 76.1 78.2 67.5 65.3 67.3

– 601,000 537,000 20 6.5 520,000 5.7 4.0

Anneal.: Thermal annealing.

The extensive morphological characteristics of the GO/Ag NWs and GO/Ag NWs/GO film were analyzed by AFM. The AFM images of the GO/Ag NWs (Fig. S2a and S2c) reveal that the Ag NWs adhered tightly to the GO sheets. AFM images of the GO/Ag NWs/ GO (Fig. S2b and S2d) show that the Ag NWs were embedded between the GO layers. To evaluate the performance of the G/Ag NWs hybrid film, the device was fabricated using G/Ag NWs film as the anode. We employed a conventional and simple device configuration of an anode/V2O5/active layer/Al (Fig. 6a). As the mismatch of the energy levels between the anode and hole transport material has a negative effect on device performance, the work function of the anode should be high and well matched to the valence band of HTL

[45]. The work functions of graphene and silver nanowire are 4.48 and 4.20 eV, respectively, which are similar to that of ITO (4.7 eV) and thus suitable for anode material. We introduced V2O5 as the hole transport layer because of excellent compatibility/wettability of vanadium precursor with G/Ag NWs. For the active layer, P3HT and PCBM were used as the electron donor and acceptor, respectively. Fig. 6b exhibits the current densityvoltage (J-V) curves of the devices based on the ITO and G/Ag NWs anode. The device with an ITO anode showed a short-circuit current density (JSC) of 7.31 mA cm
2, an open-circuit voltage (VOC) of 0.57 V, fill factor (FF) of 0.56, and power conversion efficiency (PCE) of 2.31%. In terms of electrical conductivity and transmittance, we chose G/Ag NWs film with 2-bilayer structure for device optimization. The device with 2-bilayer G/Ag NWs electrode showed a lower PCE than that of the device with ITO. A JSC of 7.21 mA cm
2, VOC of 0.52 V, FF of 0.35, and PCE of 1.30% were obtained for the device with the G/Ag NWs electrode. This situation resulted from high roughness of G/Ag NWs transparent electrode [46]. The electrical and optical performance of this hybrid electrode is still promising for future.

4. Conclusion We successfully fabricated a high performance G/Ag NWs transparent electrode as an alternative to an ITO transparent electrode using the LBL method in this work. GO thin film was prepared by

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Fig. 5. SEM images of the GO/Ag NWs films with different number of bilayers: (a) 1-bilayer, (b) 2-bilayer, and (c) 3-bilayer. Scale bar is 10 lm.

Fig. 6. (a) Device structure and (b) J-V curves of the devices based on ITO and G/Ag NWs as the anode.

spin coating on a functionalized glass substrate. After cysteamine was grafted to the surfaces of Ag NWs, the Ag NWs were deposited on the GO layer by electrostatic force using dip coating. Sodium borohydride reduction substantially improved the film conductivity. Additionally, the GO-Ag NWs hybrid electrode exhibited low sheet resistance. While a 2- bilayer hybrid film had a transmittance of 78.2% and a sheet resistance of 6.5 O sq-1, a 3-bilayer hybrid film had a transmittance of 67.3% and a sheet resistance of 4.0 O sq-1, which was comparable to ITO. Because of that, the FOM values of the 3-bilayer (214) and 2-bilayer (218) TCEs were also comparable to that of ITO (297). The P3HT:PCBM device based on 2-bilayer hybrid film as the anode exhibited PCE of 1.30%, implying that hybrid film is a promising electrode material as an alternative to conventional ITO electrode.

Acknowledgements This research was supported by the Technology Development Program to Solve Climate Changes of the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2016M1A2A2940914) as well as supported by TUBITAK (113M772).

Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2017.05.065.

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