Performance improvement of flexible ultraviolet photodetectors based on ZnO nanorod arrays by hydrothermal method with assistance of polyethyleneimine

•ZnO nanorod arrays were prepared using hydrothermal assisted with PEI.•The photodetectors based on PEI-ZnO show a quick response time (~4 s) and high responsivity (~56 A/W).•The flexible devices display reliable stability and robustness under bending tests.•Raman and XPS spectra reveal the defect mechanisms on improved performance.