Moreover, the potassium sodium niobate (KNN) nanorodbased
LINGs were fabricated by our group. As known, the
piezoelectric constant of the biocompatible KNN is much
higher than ZnO, and the free charge carrier density in
KNN is lower than ZnO. The KNN nanogenerators may
have higher electromechanical conversion efficiency than
ZnO-based nanogenerators. In our KNN-LINGs, the KNN
nanorods synthesized by hydrothermal and parallel connected
by interdigitated electrodes (IDEs) on a flexible PI
substrate. The PDMS packaged KNN LINGs can generate
parallel open-circuit voltage of about 0.1Vunder finger pressing
or bending movements [23, 45]. However, the fabrication
process of such devices is complex, which would limit the
large-scale fabrication of the nanogenerators.
In order to improve and simplify the fabrication process
of LINGs, Zhu and coauthors have carried out a scalable
sweeping-printing-method for fabricating flexible devices
with ZnO nanowire array, which were connected by parallel
stripe type of electrodes [22]. The generated open-circuit
voltage was up to 2.03V due to the series connection of
nanowires, while a peak output power density of 11mW/cm3
was obtained. Another method for one-step fabrication of
ZnO nanowire networks was reported by Xu and coworkers
[33]. As shown in Figure 9, the nanowires were directly
synthesized between the Au/Cr and Au electrodes by lowtemperature
chemical method and were oriented-aligned
with parallel to the substrate surface. By this direct integration
process,more than 700 rows of nanowires can be connected
in series to increase the output of the nanogenerator, which
is up to 1.2V in open-circuit voltage and 26 nA in shortcircuit
current at a strain rate of 2.13%/s and strain of
0.19%.