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

Investigations on the high-performance flexible ultraviolet photodetectors have been becoming one of the interesting research focuses in recent years. ZnO is considered as suitable material for ultraviolet photodetection due to its wide bandgap (~3.37 eV). In this work, ZnO nanorod arrays were prepared using the hydrothermal method at the temperature of 70 ℃ on flexible substrates. Polyethyleneimine (PEI) was added into hydrothermal solution as the growth additive to achieve the performance improvement of the ZnO nanorod arrays ultraviolet photodetector. SEM, XRD, absorption spectroscopy, Raman spectroscopy and XPS were employed to characterize the morphology, crystallinity, optical properties and chemical composition. The introduction of PEI adjusts the growth process of ZnO nanorod arrays and affects the distribution of defect states, which brings out the improvement of the optoelectronic performance of ZnO nanorod arrays ultraviolet photodetectors. Compared with pure ZnO, the higher photo to dark current ratio and responsivity, and quicker time response speed are demonstrated in the PEI-assisted ZnO nanorod arrays photodetectors. And more photoresponse parameters are also discussed and compared. Furthermore, the photodetectors also display outstanding mechanical flexibility and robustness under multiple bending cycle tests. Our work presents a potential approach for improving the optoelectronic performance of simple-operated flexible ultraviolet photodetectors.