Available on-demand - F.EL06.03.04
Graphene Oxide Encapsulated Silver Nanowire Transparent Electrodes—Stability and Device Applications
Woo Hyun Chae1,Thomas Sannicolo1,Jeffrey Grossman1
Massachusetts Institute of Technology1
Among many candidate materials that can overcome the high cost and brittleness of indium tin oxide (ITO), silver nanowire (AgNW) networks appear as a promising substitute. The percolating networks of AgNWs exhibit high flexibility and excellent optoelectronic properties, with sheet resistance of a few Ω/sq and total transmittance of 90% at 550 nm, fulfilling the requirements for many applications such as solar cells or transparent heaters.1,2 In addition, the fabrication of these electrodes can be achieved by scalable solution-based methods. However, AgNW’s susceptibility to corrosion and thermal instability remain limiting factors to its widespread market adoption. Depending on the application target, bare AgNW networks usually require stabilization by encapsulation layers to increase resilience to chemical or electrical stress.
In this study, we present a scalable and economically viable process involving electrophoretic deposition (EPD) to fabricate a highly stable hybrid transparent electrode with a sandwich-like structure where the AgNW network is covered by GO on both sides.3 The newly developed process allows the conductive transparent film to be transferred to an arbitrary surface after deposition and demonstrates excellent sheet resistance (15 Ω/sq) and transmittance (87% at 550 nm) on glass substrates. Unlike the uncoated AgNW network, the hybrid electrode was found to retain its original conductivity under long-term storage at 80○C. This chemical resilience was explained by the absence of major silver corrosion products for the AgNW encapsulated by GO as indicated by X-ray photoelectron spectroscopy (XPS).
In situ electrical ramping and resistance measurement up to 20V combined with Infrared Thermography were also conducted in order to assess the electrical stability of our electrodes. The electrical behavior of bare AgNW networks typically undergoes distinct phases comprising “optimization” (Joule-effect-induced sintering of the junctions) at first,4 then “degradation” (Joule-effect-induced morphological instabilities of some AgNWs), and finally “breakdown”. It was demonstrated experimentally that the latter breakdown stage involves the formation and propagation of a crack parallel to the contact electrodes.5 On the other hand when encapsulating in GO, the results indicate a novel stabilization mechanism enabled by the presence of GO that prevents abrupt divergence of the resistance to the MΩ range.
Finally, we will explain the benefits of using these transferrable GO-stabilized AgNW networks in devices by giving some examples of successful integration into organic solar cells (OSC). Importantly, our film can be used as a transparent top electrode for OSC, paving the way for transparent photovoltaics with longer lifetimes. Our unique double-sided EPD-GO/AgNW/GO design where GO is already integrated with the AgNW network serves a dual purpose of encapsulating the entire device as well as enhancing the contact between AgNW and underlying device stack. This results in an enhanced device performance along with increased lifetime by a factor of 5 compared to an unencapsulated device with sprayed AgNWs as top contact.
(1) T. Sannicolo, M. Lagrange, A. Cabos, C. Celle, J.-P. Simonato, D. Bellet, 2016. Small, 12 (44), 6052–6075
(2) M. Lagrange, T. Sannicolo, D. Muñoz-Rojas, B.G. Lohan, A. Khan, M. Anikin, C. Jiménez, F. Bruckert, Y. Bréchet, D. Bellet, 2017. Nanotechnology, 28 (5), 55709
(3) W.H. Chae, T. Sannicolo, J.C. Grossman, 2020, ACS Applied Materials and Interfaces, 12 (15), 17909-17920
(4) T. Sannicolo, D. Muñoz-Rojas, N.D. Nguyen, S. Moreau, C. Celle, J.-P. Simonato, Y. Bréchet, D. Bellet, 2016. Nano Letters, 16 (11), 7046–7053
(5) T. Sannicolo, N. Charvin, L. Flandin, S. Kraus, D.T. Papanastasiou, C. Celle, J.-P. Simonato, D. Muñoz-Rojas, C. Jiménez, D. Bellet, 2018. ACS Nano, 2018, 12, 4648−4659