Quantum dot-sensitized solar cells (QDSCs) have been attracting much attention due to their unique characteristics such as multiple exciton generation and a tunable band gap. Supporting materials of photoelectrodes for QDSCs like TiO2 and ZnO are some of the most important parts because they absorb sensitizers and also function as photo-injected electron pathways. Particularly, ZnO has many advantages for the photoelectrodes of QDSCs. In this study, we investigated the effect of ammonia treatment on ZnO nanoflower-based QDSCs by varying the concentration of ammonia. The influence of ammonia treatment is discussed with respect to the power conversion efficiency from the J-V curve, electrochemical impedance spectroscopy (EIS), and other analyses. (C) 2014 Elsevier Ltd. All rights reserved.