Solid oxide fuel cells with thin electrolyte of two types, Sm0.2Ce0.8O1.9 (SDC) (15 mu m) single-layer and 8 mol% Yttria stabilized zirconia (YSZ) (5 mu m) + SDC (15 mu m) bi-layer on NiO-YSZ cermet substrates were fabricated by screen printing and co-firing. A Sm0.5Sr0.5CoO3 cathode was printed, and in situ sintered during a cell performance test. The SDC single-layer electrolyte cell showed high electrochemical performance at low temperature, with a 1180 mW cm(-2) peak power density at 650 degrees C. The YSZ + SDC bi-layer electrolyte cell generated 340 mW cm(-2) peak power density at 650 degrees C, and showed good performance at 700-800 degrees C, with an open circuit voltage close to theoretical value. Many high Zr-content micro-islands were found on the SDC electrolyte surface prior to the cathode preparation. The influence of co-firing temperature and thin film preparation methods on the Zr-islands' appearance was investigated. (c) 2006 Elsevier B.V. All rights reserved.