Other Applications - Hierarchical Nanostructures for Energy Devices - page 270

also because the high temperature annealing process to improve junction
resistance is not compatible with heat sensitive flexible or stretchable sub-
strates. To address this current issue in metal nanowire percolation network
transparent conductors, Lee et al. 1,27 presented a series of combined novel
approaches to develop a very long Ag NW synthesis method and applied it as
a new type of high performance flexible and transparent metal conductor
combined with a low temperature nano-welding process as shown in
Figure 12.1. Very long metallic NWs are critical factors enabling the high
transparency, high electrical conductivity and superior mechanical com-
pliance and strength at the same time, which are usually hard to achieve
simultaneously. We found that very long metallic nanowire percolation
network conductors combined with a low temperature nano-welding process
enabled highly transparent flexible conductors with high transmittance (90-
96%) and high electrical conductivity (9-70 ohm sq 1 ) with good mechanical
strength. These values beat the other related class of reported flexible and
transparent conductors including carbon-based nanomaterials (CNT and
graphene) and other metallic nanomaterial-based devices. To demonstrate
the feasibility of our approach for high performance transparent and flexible
conductors, a fully functioning transparent touch panel and highly flexible
LED circuits were demonstrated for the first time as shown in Figure 12.2.

d n 3 r 4 n g | 8

.

Figure 12.1 Nano-welding of a very long Ag NW network electrode for highly
transparent and flexible electrodes. (A) Magnified SEM (pseudo-col-
ored) and (B) HRTEM images of nano-welded spots between very long
Ag NWs at optimum processing conditions. Note the high crystalline
characteristics of each NW and the nano-welded spot between Ag NWs.
The HRTEM sample was prepared by focused ion beam (FIB).
Reproduced with permission from ref. 1.