3.3.2. Post Print Processing

NW networks are often cured without sintering because the particles naturally contact when randomly dispersed, but welding NWs can significantly reduce wire-to-wire resistances when significant PVP coatings are present. For instance, Lee et al. used thermal sintering at 200 ◦C for 20 min to reduce resistance in a printed AgNW trace from 1000 to 100 Ω/sq [118] and Li et al. photonically welded NWs to reduce sheet resistances from 53 to 7.1 Ω/sq [23]. An example SEM image of laser-welded AgNWs is provided in Figure 7c [119]. Finally, NWs can be welded by NPs embedded in a matrix film. In one demonstration, Triambulo created a highly conductive (5.0–7.3 <sup>×</sup> <sup>10</sup><sup>5</sup> S/m) AgNW-AgNP matrix film on a flexible PET substrate with similar optical transmittance (>90%) compared to a pure AgNW film, and SEM images of the resultant network are provided in Figure 7d [120]. Despite the advantages of welding NWs for improving conductivity, the ability to process NWs at room temperature for many ink formulations is a key advantage in roll-to-roll integration, especially when attempting to limit start-up costs [11].
