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. 2022 Sep 1;13(9):1450.
doi: 10.3390/mi13091450.

Effects of Group-I Elements on Output Voltage Generation of ZnO Nanowires Based Nanogenerator; Degradation of Screening Effects by Oxidation of Nanowires

Mansoor Ahmad  1 , M K Ahmad  1 , M H Mamat  2 , A Mohamed  3 , A B Suriani  3 , N M A N Ismail  1 , C F Soon  1 , N Nafarizal  1
Affiliations

Effects of Group-I Elements on Output Voltage Generation of ZnO Nanowires Based Nanogenerator; Degradation of Screening Effects by Oxidation of Nanowires

Mansoor Ahmad et al. Micromachines (Basel). .

Abstract

Here, we report the successful incorporation of group I elements (K, Na, Li) to ZnO nanowires. Three distinct (2, 4, and 6 wt.%) doping concentrations of group I elements have been used to generate high piezoelectric voltage by employing a vertically integrated nanowire generator (VING) structure. X-ray photoelectron spectra (XPS) indicated the seepage of dopants in ZnO nanowires by substitution of Zn. Shallow acceptor levels (LiZn, NaZn, KZn) worked as electron trapping centers for intrinsically n-type ZnO nanowires. Free moving electrons caused a leakage current through the nanowires and depleted their piezoelectric potential. Reverse leakage current is a negative factor for piezoelectric nanogenerators. A reduction in reverse leakage current signifies the rise in output voltage. A gradual rise in output voltage has been witnessed which was in accordance with various doping concentrations. K-doped ZnO nanowires have generated voltages of 0.85 V, 1.48 V, and 1.95 V. For Na-doped ZnO nanowires, the voltages were 1.23 V, 1.73 V, and 2.34 V and the voltages yeilded for Li-doped ZnO nanowires were 1.87 V, 2.63 V, and 3.54 V, respectively. Maximum voltage range has been further enhanced by the surface enrichment (oxidized with O2 molecules) of ZnO nanowires. Technique has been opted to mitigate the screening effect during an external stress. After 5 h of oxidation in a sealed chamber at 100 ppm, maximum voltage peaks were pronounced to 2.48 V, 3.19 V, and 4.57 V for K, Na, and Li, respectively. A low-cost, high performance mechanical transducer is proposed for self-powered devices.

Keywords: Schottky contact; VING; ZnO nanowires; nanogenerator; piezoelectric potential.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic diagram of ZnO based VING and oxidized ZnO nanowire.
Figure 2
Figure 2
SEM images of ZnO nanowires, (a) pristine ZnO nanowires, (b) Li-doped ZnO nanowires, (c) Na-doped ZnO nanowires, and (d) K-doped ZnO nanowires.
Figure 3
Figure 3
Histogram showing diameter range of ZnO nanowires, (a) pristine ZnO nanowires, (b) Li-doped ZnO nanowires, (c) Na-doped ZnO nanowires, (d) K-doped ZnO nanowires.
Figure 4
Figure 4
XRD pattern of vertically grown ZnO nanowires, (a) Na-doped ZnO nanowires, (b) K-doped ZnO nanowires (c) Li-doped ZnO nanowires, and (d–l) concentration mapping of doped Li, Na, and K, respectively.
Figure 4
Figure 4
XRD pattern of vertically grown ZnO nanowires, (a) Na-doped ZnO nanowires, (b) K-doped ZnO nanowires (c) Li-doped ZnO nanowires, and (d–l) concentration mapping of doped Li, Na, and K, respectively.
Figure 4
Figure 4
XRD pattern of vertically grown ZnO nanowires, (a) Na-doped ZnO nanowires, (b) K-doped ZnO nanowires (c) Li-doped ZnO nanowires, and (d–l) concentration mapping of doped Li, Na, and K, respectively.
Figure 5
Figure 5
XPS spectra, (a) Zn 2p (b) O 1s, (c) Li 1s, (d) K 2p, and (e) Na 1s.
Figure 5
Figure 5
XPS spectra, (a) Zn 2p (b) O 1s, (c) Li 1s, (d) K 2p, and (e) Na 1s.
Figure 6
Figure 6
Output voltage values generated by ZnO nanowires based VING, (a) as- grown, (c) 2%K/ZnO (d) 4% K/ZnO (e) 6% K/ZnO (b) voltage histogram, (f) voltage bar graph for various K doping concentrations.
Figure 6
Figure 6
Output voltage values generated by ZnO nanowires based VING, (a) as- grown, (c) 2%K/ZnO (d) 4% K/ZnO (e) 6% K/ZnO (b) voltage histogram, (f) voltage bar graph for various K doping concentrations.
Figure 7
Figure 7
Output voltage values generated by ZnO nanowires based VING, (a) as-grown, (c) 2%Na/ZnO (d) 4% Na/ZnO (e) 6% Na/ZnO (b) voltage histogram, (f) voltage bar graph for various Na doping concentrations.
Figure 8
Figure 8
Output voltage values generated by ZnO nanowires based VING, (a) as-grown, (c) 2% Li/ZnO (d) 4% Li/ZnO (e) 6% Li/ZnO, (b) voltage histogram, and (f) voltage bar graph for various Li doping concentrations.
Figure 9
Figure 9
Output voltage values generated by ZnO nanowires based VING oxidized for 5 h, (a) 6%K/ZnO, (b) 6%Na/ZnO, (c) 6% Li/ZnO, (d) voltage increment by changing load resistance, and (e) voltage comparison for all three cases with and without oxidation.
Figure 9
Figure 9
Output voltage values generated by ZnO nanowires based VING oxidized for 5 h, (a) 6%K/ZnO, (b) 6%Na/ZnO, (c) 6% Li/ZnO, (d) voltage increment by changing load resistance, and (e) voltage comparison for all three cases with and without oxidation.
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