Supporting Information - IOPscience

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networks via spin coating at 2500, 1500 and 1000 rpm. Pressing during annealing were also evaluated for minimizing the roughness values of the networks.
Supporting Information Optimization of Silver Nanowire Networks and Their Utilization in Polymer Light Emitting Diodes Sahin Coskun, Elif Selen Ates and Husnu Emrah Unalan* Department of Metallurgical and Materials Engineering, Middle East Technical University, Ankara, Turkey (06800). Tel:+ 90 312 210 5939 Fax: +90 312 210 25 18 *e-mail: [email protected]

Figure S1 shows effect of annealing process at 200°C for 30 min on optoelectronic properties of Ag NW networks. As it can be seen from the graph, annealing does not effect the transmittance of Ag NW networks. However, sheet resistance of Ag NW networks decreases dramatically with annealing.

Figure S1. Effect of annealing on the optoelectronic properties of Ag NW networks with different nanowire densities.

Figure S2 (a) shows the variation in the sheet resistance values of the Ag NW networks fabricated in this work taken from various locations on a substrate. A mean sheet resistance of 6.8 Ω/sq has been obtained, were the maximum and minimum sheet resistance of 8 and 5 Ω/sq were measured, respectively for that particular sample. This result reveals the uniformity of the Ag NW networks fabricated through simple spray coating. This clearly indicates that transparent and conducting Ag NW networks can be reproducibly produced via spray coating without any substrate size limit. Figure S2 (b) shows current versus time graph, in other words, the current carrying capacity for the Ag NW networks, in comparison to commercially available ITO. For this purpose, a constant voltage (1.5 V) was applied to these samples for 14 hours. Both samples were found to be still conductive after 14 hours. As it is seen from the graph, Ag NW networks were found to be highly stable, more than ITO under constant voltage.

Figure S2. (a) Sheet resistance variation of Ag NW networks. (b) Current stability of commercially available ITO and the Ag NW networks fabricated in this work.

The PEDOT:PSS deposition onto Ag NW networks with same sheet resistance and RMS roughness values were conducted. Right after spin coating, composite thin films were annealed at 100°C for 20 minutes in a vacuum oven. In the first part of the experiments, PEDOT: PSS were diluted with isopropyl alcohol (IPA) at a volume ratio of 1:1. This was done to improve the solvent evaporation and wettability of the polymer layer. In the second part, pure PEDOT: PSS solution was used. PEDOT: PSS solutions were coated onto Ag NW networks via spin coating at 2500, 1500 and 1000 rpm. Pressing during annealing were also evaluated for minimizing the roughness values of the networks. Figure S3 (a)-(h) shows AFM 3D images of Ag NW networks that have all been treated differently. Comparing the AFM images, it can be said that the covering ability of PEDOT:PSS increases as spin coating speed decreases. Moreover, since IPA quickly evaporates after spin coating, pure PEDOT: PSS forms thicker films than PEDOT: PSS / IPA mixture solution under the same spin coating rate. As it is shown in Figure S3 (g) and (h), when pure PEDOT: PSS was spin coated at 1500 and 1000 rpm, respectively, it totally covers Ag NW networks without any discernible nanowire features on the substrates.

Figure S3. AFM 3D images of Ag NW networks that are (a) as deposited, (b) pressed during annealing, PEDOT:PSS/ IPA spin coated at (c) 2500, (d) 1500, (e) 1000 rpm, PEDOT:PSS spin coated at (f) 2500, (g) 1500 and (h) 1000 rpm.

Figure S4 shows the change in RMS roughness values with the PEDOT: PSS coating processes. As-deposited Ag NW networks have a RMS roughness of approximately 54 nm. Pressing during standard annealing process (200°C for 30 minutes) decreases the RMS roughness value down to 42 nm. Spin coating the PEDOT: PSS / IPA solution at 2500 rpm, RMS roughness decreases to 25 nm. Conducted experiments revealed that, this RMS roughness value was enough for the fabrication of a PLED. For various other applications, by simply adjusting the spin coating parameters, desired RMS roughness values can be obtained. An RMS roughness value down to 4 nm was obtained for Ag NW network that were coated with PEDOT: PSS spin coated at 1000 rpm.

Figure S4. RMS roughness values for Ag NW networks.