Photoluminescence and photoconductance in annealed ZnO thin films

Drastic evolution of point defects in vertically grown ZnO nanorods induced by lithium ion implantation

The evolution of various point defects in 100 keV lithium (Li) ion-implanted ZnO nanorods (NRs) by varying the fluences from 1 × 10¹⁴ to 7 × 10¹⁵ ions per cm² has been investigated experimentally and using a simulation by stopping and range of ions in matter (SRIM). The X-ray photoelectron spectroscopy results indicate that the Li¹⁺ ions have been incorporated at Zn²⁺ sites, which forms Li_Zn acceptors in the implanted NRs. The structural disorder and the number of oxygen vacancies in the implanted ZnO NRs increase drastically with an increase in the Li fluence as indicated by the X-ray diffractometry and Raman scattering analyses. Both the formation of acceptors and implantation-induced defects make the Li-implanted NRs electrically highly resistive. The yellow-orange photoluminescence (PL) emission of the as-grown ZnO NRs has evolved into green emission in the implanted NRs. A suppression of the green PL at higher fluences is possibly due to an apparent decrease in the zinc vacancy concentration. The SRIM results explain the quantitative energy loss, the distributions of the implanted Li ions and the point defects along the target ZnO NRs. The consistency between the experimental and theoretical simulations validates our analyses on the formation and evolution of various point defects in highly resistive Li-implanted ZnO NRs.

Fabrication of Self-Powered Fast-Response Ultraviolet Photodetectors Based on Graphene/ZnO:Al Nanorod-Array-Film Structure with Stable Schottky Barrier

A Schottky UV photodetector based on graphene/ZnO:Al nanorod-array-film (AZNF) structure has been fabricated. Different from the previously reported graphene/ZnO photodetectors, this photodetector has a stable Schottky barrier which does not disappear under UV light. Thus, the UV photodetector can work as a high-performance self-powered device. The key to improve the stability of the Schottky barrier is a two-step surface treatment process. As a result, the self-powered photodetector exhibits a UV-to-visible rejection ratio of about 1 × 10², a responsivity of 0.039 A W^1-, a short rise time of 37 μs, and a decay time of 330 μs. Furthermore, the photodetector is able to keep the responsivity under low light conditions. In comparison with the previously reported graphene/ZnO UV photodetectors, the photodetector exhibits a higher responsivity at zero bias and a faster response speed. This study provides a potential way to fabricate high-performance self-powered UV photodetectors.

Fabrication of nanostructured ZnO film as a hole-conducting layer of organic photovoltaic cell

We have investigated the effect of fibrous nanostructured ZnO film as a hole-conducting layer on the performance of polymer photovoltaic cells. By increasing the concentration of zinc acetate dihydrate, the changes of performance characteristics were evaluated. Fibrous nanostructured ZnO film was prepared by sol-gel process and annealed on a hot plate. As the concentration of zinc acetate dihydrate increased, ZnO fibrous nanostructure grew from 300 to 600 nm. The obtained ZnO nanostructured fibrous films have taken the shape of a maze-like structure and were characterized by UV-visible absorption, scanning electron microscopy, and X-ray diffraction techniques. The intensity of absorption bands in the ultraviolet region was increased with increasing precursor concentration. The X-ray diffraction studies show that the ZnO fibrous nanostructures became strongly (002)-oriented with increasing concentration of precursor. The bulk heterojunction photovoltaic cells were fabricated using poly(3-hexylthiophene-2,5-diyl) and indene-C60 bisadduct as active layer, and their electrical properties were investigated. The external quantum efficiency of the fabricated device increased with increasing precursor concentration.

A novel and simple approach to enhance ultraviolet photosensitivity: activated-carbon-assisted growth of ZnO nanoparticles

An activated-carbon (AC) assisted route is developed to synthesize a ZnO nanoparticle network. The route involves simple addition of AC to the solution containing the zinc salt and finally removing them by burning at higher temperature to form a sponge-like porous ZnO nanoparticles. The surface area measurements show that AC-assisted ZnO nanoparticles (AC-ZnO) have a higher surface area than those synthesized without AC (B-ZnO), which is further confirmed by the field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM) images. Ultraviolet (UV) absorbance results show that the optical quality remains almost unchanged for both types of nanoparticles. Enhanced and faster UV photosensitivity has been observed for the AC-ZnO. The change in the UV photosensing properties demonstrated here provides a new approach to synthesizing other high surface area materials for novel physical and chemical properties.