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To minimize alteration of the La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF)/Gd 0.2 Ce 0.8 O 2-δ (CGO20)/Y 0.06 Zr 0.94 O 2-δ (3YSZ) interface via strontium zirconate formation in solid oxide cells, electron beam physical vapor deposition was employed to manufacture dense, thin gadolinium-doped ceria (CGO) interlayers. CGO layers with thicknesses of 0.15, 0.3, and 0.5 μm were integrated in state-of-the-art 5 × 5 cm 2 -large electrolyte-supported cells, and their performance characteristics and degradation behavior were investigated. Electrochemical impedance spectroscopy measurements are correlated with a postmortem scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis to show that 0.15 μm-thick layers lead to the formation of a continuous Sr-containing secondary phase at the CGO/YSZ interface, likely related to the formation of a SrO-ZrO 2 phase. Major performance losses were confirmed by an increase in both Ohmic and polarization resistance with an increase in the frequency region ∼10 3 Hz. Cells with 0.3 μm- and 0.5 μm-thick CGO layers showed similar high performance and low degradation rates over a testing period of ∼800 h. The YSZ/CGO interface of the cells with a 0.3 μm-thick CGO layer showed the formation of a discontinuous Sr-containing secondary phase; however, performance losses were still successfully prevented. Furthermore, it is observed that 0.5 μm-thick CGO layers were sufficient to suppress the formation of the Sr-containing secondary phase.