Transparent electrodes are a necessary component in a number of devices such as touch screens, liquid crystal displays, and organic light-emitting diodes. The most commonly used transparent conductor, indium tin oxide (ITO), is expensive, has limited mechanical flexibility, and requires high deposition temperatures. Recent advances in nanomaterials have generated alternatives to ITO. Of the various materials, films consisting of random networks of solution-synthesized silver nanowires have emerged as a leading candidate [1
]. Current conducts through the nanowires while light is able to pass through the open spaces between the nanowire networks. We have synthesized the nanowire films that have transparency and conductivity values better than competing new flexible technologies (e.g., carbon nanotube films, graphene, conductive polymers) and comparable to ITO. Furthermore, the nanowire electrodes are inexpensive, flexible, and compatible with roll-to-roll deposition techniques.
In addition, silver nanowire electrodes also scatter a portion of the transmitted light [3
], making these electrodes particularly attractive for use in solar cells. Indeed, there are numerous reports about the promising device characteristics of organic solar cells using silver nanowire electrodes [4
]. Silver nanowires are known to oxidize and corrode over a period of months in air [6
]; however, there are no studies on the stability of the nanowire electrodes during use (i.e., when they are conducting current). In contrast to ITO where current conducts throughout the entire area of the film, in nanowire electrodes, electronic transport occurs only through the metal wire pathways, and these nanowire pathways have diameters less than 100
nm. Because of this, although the current densities generated in organic solar cells are relatively low (on the order of 10
, with the best performing devices generating about 17
]), the resulting current densities in the nanowires are very high. For example, if we assume that half of the nanowires in 12
Ω/sq silver nanowire electrodes participate in current conduction, a solar cell current density of 17
(i.e., total current divided by the total top surface area of the film) would result in an approximate current density in the nanowires of 4
(i.e., current flowing through a single nanowire divided by its cross-sectional area)a
. For comparison, this same current flowing through a 250-nm thick ITO film results in a cross-sectional current density of 103
, more than an order of magnitude less.
In this paper, it is shown that at current density levels incurred in organic solar cells, silver nanowire electrodes fail in a matter of days. We report how parameters such as sheet resistance and current density affect the time to failure, as well as characterize the electrodes to investigate the failure mechanism.