The widely used cathode La0·7Sr0·3Co0·5Fe0·5O3-δ (LSCF) perovskite and excellent electrolyte LaPr-codoped ceria (LCP) are combined into a double-layer LSCF-LCP electrolyte. Leveraging the semiconductor-ion material nature, a built-in electric field (BIEF) is established at the junction between the semiconductor LSCF and ionic conductor LCP layers to enhance ionic transport, consequently improving fuel cell power output. Comparative research on the double-layer LCP with LSCF brushing thin films, varying LSCF thickness from 50 μm to 150 μm, reveals that the LSCF layer with 100 μm thickness yields the highest fuel cell power output, 567 mW/cm2 at 450 °C. Based on analysis of experimental results, we attribute these intriguing properties to the enhanced ion transport and delves into the BIEF effect. This study presents alternative avenues for advancing fuel cell technologies, offering insights valuable for research and development.