In this study, the Y2O3 doping concentration of yttria stabilized zirconia (YSZ) thin film electrolyte deposited by plasma enhanced atomic layer deposition (PEALD) is optimized to maximize the performance of thin film solid oxide fuel cells (TF-SOFCs). The PEALD YSZ thin films are highly crystalline, and the Y2O3 concentration is controlled by changing the ratio between ZrO2 and Y2O3 ALD cycles. Electrochemical performances of TF-SOFCs are strongly dependent on the Y2O3 doping concentration in electrolytes. The cell with 10.7 mol% doped YSZ achieves the best performance (180 mW/cm(2)) at 450 degrees C due to decreased polarization loss because of its higher density of oxygen vacancies. These results demonstrate the effectiveness of PEALD process to deposit crystalline YSZ thin film electrolytes with optimal doping for high performance TF-SOFCs. (C) 2019 Published by Elsevier Ltd.