3.3.2. Comparison of Paste Inks Prepared with Vehicle 2

Paste inks containing copper nitride, copper(II) oxide, or copper(I) oxide were prepared with vehicle 2 and subjected to IPL sintering (sintering conditions, Table 4; copper conversion ratio and sheet resistance, Table 5; X-ray diffraction patterns, Figure S7). The appearances of the samples before and after IPL irradiation are shown in Figure 7. For the copper nitride films, the surface color was clearly changed from dark to light brown. In contrast, the color of the copper(II) oxide and copper(I) oxide films remained largely unchanged (minor changes were observed for copper(II) oxide under conditions P.S.3 and P.S.4).

**Figure 7.** Appearance of films prepared with vehicle 2 and containing (Cu3N), copper(I) oxide (Cu2O), or copper(II) oxide (CuO) before and after intense pulsed light irradiation under the conditions shown in Table 4.

The sheet resistances of the copper(II) oxide and copper(I) oxide films could not be determined because they were beyond the maximum limit of quantitation of the instrument (>9.999 × <sup>10</sup><sup>7</sup> <sup>Ω</sup>). Thus, in the case of copper(I) oxide film, sheet resistance was not improved despite the film having improved mechanical strength compared to the film prepared by liquid ink.
