ZnO Nanorods (NRs) are deposited on glass substrate using the hydrothermal method by applying a strategic growth control to improve their aspect ratios. In this research, the aspect ratio was tuned by tailoring the synthesis parameters, including the seed layer annealing temperature, absence/presence of polyethylenimine (PEI) in the growth solution, and the solution preheating process. The effects of these parameters on the morphology, crystal structure, room temperature photoluminescence properties, and current-voltage characteristics were examined by FESEM, XRD, PL, and I-V measurements. It was demonstrated that by varying the seed layer annealing temperature and presence of PEI solution as well as implementation of the solution preheating process, the aspect ratio of the NRs was increased from 7.9 to 64.4. The ZnO NRs with the high aspect ratio of 64.4, achieved from the solution containing PEI additive preheated at 95 °C for 1 h on the ZnO seed layer annealed at 250 °C that exhibited a maximum bandgap energy (3.32 eV), the highest responsivity of 4.5 mA/W, and the shortest response time (1.1 s). The UV photo detection performance of the deposited NR was improved by enhancing their aspect ratios. Finally, from the application point of view, the optimum value of responsivity is significantly increased to 44.1 mA/W using the deposited nanorods in the FTO/ZnO NRs/FTO device structure.