Abstract Electron transporting later (ETL) with nanorod structure provides a special passage for which free electrons can easily travel through the layer. ETL also helps to prevent the recombination and to enhance the attaching ability of the perovskite layer and thus improving the conversion efficiency of the perovskite solar cell. In this work, the investigation on the hydrothermal process of n-type ZnO nanorods (ZnO NRs) layer is carried out at the temperature below 100 °C and under the atmospheric pressure. Four concentrations of aqueous precursor solution consisting of zinc nitrate hexahydrate and hexamethylenetetramine are used in the experiment (25 mM, 50 mM, 75 mM and 100 mM). Subsequently, the perovskite solar cells, with normal structure of FTO-glass/ZnO dense layer/ZnO NRs/PCBM/Perovskite/P3HT/Ag, are fabricated. The optimum power conversion efficiency of 2.26% was obtained from the device prepared with 100 mM precursor solution. The concentration of solution used in the hydrothermal process affects the size and density of ZnO NRs and, in turn, affects the conversion efficiency of the cells.