To develop more highly-efficient SOFCs, we have investigated the thickness of highly resistive layer which consist of solid solutions of CeO2-ZrO2 system generally observed between YSZ electrolyte and cathode-interlayer made of doped CeO2. In terms of the effect of the dopant in the CeO2-based interlayer materials on the thickness of the solid solution, the use of YDC or LDC for the interlayer results in a thinner solid solution compared to that obtained when a GDC interlayer was used. When adapted into SOFCs, I-V tests at 800 degrees C indicated that the cell with a YDC interlayer exhibited substantially better performance than the cell with a GDC interlayer. (C) 2015 Elsevier B.V. All rights reserved.