A paste (32) for use in metallization of a solar cell (12) includes an organic vehicle (44) and a mixture of copper-containing particles (46), metal-oxide-containing nanoparticles (50), and secondary oxide particles (52) different from the metal-oxide-containing nanoparticles (50). The secondary oxide particles (52) include particles (42) of a metal oxide and a metal of the metal oxide capable of reducing at least some of the metal-oxide-containing nanoparticles (50) to metal when heated. The organic vehicle (44) is capable of reducing the metal oxide of the secondary oxide particles (52) upon decomposition of the organic vehicle (44). A paste (32) includes a mixture of particles (42) including metallic copper particles (46), nanoparticles (50), and metal oxide particles (52) in the organic vehicle (44). The nanoparticles (50) include at least one oxide of nickel, copper, cobalt, manganese, and lead. The metal oxide of the metal oxide particles (52) has a more negative Gibbs Free Energy of Formation than a metal oxide of the at least one oxide of the nanoparticles (50).