A highly conductive and transparent oxide/metal/oxide (OMO) multilayer transparent electrode is developed by flash lamp annealing (FLA). A transient thermal effect of FLA on the sandwich structure of the ultrathin Ag layer and zinc-doped indium oxide (IZO) layer is systematically investigated. FLA enables IZO/Ag/IZO multilayer to maintain the continuous ultrathin Ag interlayer and improve the crystallinity of the IZO layers. This is due to a very short processing time, absorption of visible light by the Ag layer, heat transfer from the Ag layer to the IZO layer, and mechanical constraint of the Ag layer by neighbor IZO layers. This combination of continuous ultrathin Ag layer and highly crystalline IZO layer decreases light scattering in a visible range and allows the electron donation from the Ag layer of a high electron concentration to neighbor IZO layers of a high electron mobility. IZO/Ag/IZO multilayer film from an optimal FLA process achieves a very low sheet resistance of 4.1 Ω sq^-1 and a high optical transmittance (90.1%) in the broadband range of 400-800 nm. A perovskite solar cell in the best IZO/Ag/IZO transparent electrode exhibits better current generation and higher fill factor than a device of FTO electrode.