The chemical side reaction between a lanthanum strontium cobalt ferrite (LSCF) cathode and an yttria-stabilized zirconia (YSZ) electrolyte is a key problem for solid oxide fuel cell (SOFC) fabrication. Herein, we demonstrate rapid fabrication of an LSCF cathode using a novel flash light sintering (FLS) technique to suppress the chemical side reaction; notably, no Gd-doped ceria interlayer is required. The FLS-fabricated LSCF cathode shows comparable crystalline development and microstructural evolution to a cathode fabricated using the conventional high-temperature sintering process. A clear LSCF/YSZ interface appears, indicating suppression of detrimental chemical side reactions via rapid and surface-dominant sintering kinetics. Detailed interfacial microstructure analysis reveals the absence of Sr segregation and SrZrO3 formation at the FLS-LSCF cathode/YSZ electrolyte interface. Remarkable performance of 0.9 W cm–2 power density at 750 °C is achieved for a cell incorporating the rapidly fabricated LSCF cathode on the interlayer-free YSZ electrolyte owing to suppression of the insulating secondary phases and significantly reduced polarization resistance. Hence, rapid LSCF cathode fabrication via the novel FLS method effectively suppresses secondary phase formation at the LSCF/YSZ interface and greatly simplifies SOFC fabrication by eliminating the doped-ceria-based interlayer. Moreover, this novel method could help overcome interfacial chemical reaction problems in various solid-state devices, while also providing new application opportunities for high-performance electrolyte/electrode materials.