Effect of contact area and depth between cell cathode and interconnect on output power density and degradation of stack for planar SOFCs has been investigated systematically. The results indicate that the maximum output power density (MOPD) of repeating units inside stack increases firstly and then decreases slightly with the increasing interface contact area and depth, respectively, showing an approximate convex parabolic relation of power density to interface contact area and depth. The degradation rate of repeating units decreases gradually for 972 h' operation under 0.75 V unit-cell voltage, 0.476 A cm(-2) current density and 41.8% fuel utilization with different contact area. At the optimum value of the interface contact area, the repeating unit inside stack appears no degradation under operation for 1060 h under 0.8 V unit-cell voltage, 0.444 A cm(-2) current density, and 78% fuel utilization efficiency. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.