Layered double hydroxides (LDHs) have been extensively investigated for various applications such as drug delivery, energy storage, catalysis, and luminescence. In this study, an eco-friendly ZnAl–CO3–LDH-poly(vinylidene fluoride) (ZnAl–LDH–PVDF) composite acting...

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This paper presents a highly cost-effective design for an aluminum (Al) foil-based ZnO/Ag/ZnO-stacked piezoelectric nanogenerator (ZAZ-NG) fabricated using radio frequency magnetron sputtering. Both Al foil sheets and a silver (Ag) paste layer are utilized to make a ZAZ-NG composed of an Ag paste layer sandwiched between two zinc oxide (ZnO) layers. The output voltages of the ZAZ-NGs with various ZnO thicknesses are measured for three different bending strains. As a result, the devices could generate a relatively high peak-to-peak output voltage (Vpp) of up to 2.5 V, which is 28 times higher than that of the single ZnO layered device. In addition, the device performance shows a strong dependence on the thickness of the ZnO layer. Moreover, the ZAG-NG device is structurally stable and can be fabricated using cost-effective methods.

Recent studies have focused on the development of efficient, flexible, and highly sensitive ultraviolet photodetectors (UV PDs) with various wide band-gap materials. In the present study, the application of environmentally friendly zinc−aluminum layered double hydroxide (ZnAl−CO 3 :LDH) is demonstrated for a high-performance, flexible UV PD. The vertically oriented ZnAl:LDH nanosheets (ZnAl:LDH Ns) are facilely synthesized by dipping the sputtered 10 wt % aluminum-doped zinc oxide thin films in deionized water at room temperature. Without passivation, the UV PDs exhibit an exceptional light-to-dark current ratio of 10 4 and a responsivity of ∼34.7 mA/W at a bias of 1 V. Moreover, the spectral responsivity and detectivity are enhanced to ∼148.3 mA/W and 2.5 × 10 12 Jones, respectively, by passivating the ZnAl:LDH Ns with polydimethylsiloxane (PDMS), thus making the device suitable for application in UV detectors. In addition, the ambient atmosphere effect on PD performance, which elucidates the clear understanding of the PD working mechanism, is also investigated. The passivation of the Ns by PDMS also helps to enhance the mechanical robustness and long-term stability of the PD. The methodology demonstrated herein highlights the potential of the ZnAl:LDH material in realizing the next generation of flexible UV PDs.

Abstract:In this paper, we present a study of various ZnO/SiO 2 -stacked thin film structures for flexible micro-energy harvesting devices. Two groups of micro-energy harvesting devices, SiO 2 /ZnO/SiO 2 micro-energy generators (SZS-MGs) and ZnO/SiO 2 /ZnO micro-energy generators (ZSZ-MGs), were fabricated by stacking both SiO 2 and ZnO thin films, and the resulting devices were characterized. With a particular interest in the fabrication of flexible devices, all the ZnO and SiO 2 thin films were deposited on indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrates using a radio frequency (RF) magnetron sputtering technique. The effects of the thickness and/or position of the SiO 2 films on the device performance were investigated by observing the variations of output voltage in comparison with that of a control sample. As a result, compared to the ZnO single-layer device, all the ZSZ-MGs showed much better output voltages, while all the SZS-MG showed only slightly better output voltages. Among the ZSZ-MGs, the highest output voltages were obtained from the ZSZ-MGs where the SiO 2 thin films were deposited using a deposition power of 150 W. Overall, the device performance seems to depend significantly on the position as well as the thickness of the SiO 2 thin films in the ZnO/SiO 2 -stacked multilayer structures, in addition to the processing conditions.

In this letter, we present the fabrication and characterization of a zinc oxide (ZnO)-based nanogenerator for piezoelectric micro-energy harvesting by combining thin films of amorphous silicon (a-Si) and ZnO. We utilized the a-Si thin film as an interlayer to assemble several a-Si/ZnO-stacked piezoelectric nanogenerators (SZPNGs) on indium tin oxide (ITO)-coated polyethylene naphthalate substrates. We investigated the influence of the a-Si layer thickness on the output voltages of the SZPNGs and demonstrated the existence of an optimal a-Si thickness for maximizing the output voltage. Overall, the SZPNGs generated higher output voltages than a conventional ZnO-based piezoelectric nanogenerator (ZPNG) lacking an a-Si interlayer, indicating enhanced performance. In particular, the SZPNG based on the optimal a-Si thickness exhibited a sixfold higher output voltage compared with the conventional ZPNG. This improved performance was ascribed to a combination of the Schottky barrier at the ITO/a-Si interface, preventing the screening effect and the relatively high dielectric constant (εr≈13) of a-Si, minimizing the loss of the piezoelectric potential induced in the ZnO layer. The results herein are expected to assist the development of even more advanced ZnO-based piezoelectric nanogenerators in the future.

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