# Strategic Development of Piezoelectric Nanogenerator and Biomedical Applications
## 3 Strategies
### Doping and Compositing
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Sr. No**} & \multicolumn{1}{c}{**Material**} & \multicolumn{1}{c}{**Morphology**} & \multicolumn{1}{c}{**Synthesis**} & \multicolumn{1}{c}{**Operation**} & \multicolumn{1}{c}{**Output**} & \multicolumn{1}{c}{**Output**} & \multicolumn{1}{c}{**Power**} & \multicolumn{1}{c}{**Ref.**} \\ \hline \multirow{8}{*}{2.} & \multirow{4}{*}{PZT} & \multirow{4}{*}{Nanoflake} & Aqueous precipitation method & Room temperature & 110 & 67 \(\mu\)A/cm\({}^{2}\) & - & [63] \\ \cline{3-8}  & & & Leaser lift off (LLO) & - & 200 & 150 \(\mu\)A/cm\({}^{2}\) & \begin{tabular}{c} 17.5 \\ \(\mu\)W/cm\({}^{2}\) \\ \end{tabular} & [67] \\ \cline{2-8}  & & \multirow{2}{*}{Nanorod} & Hydrothermal & 180 \({}^{\circ}\)C & 8 & - & \
\begin{tabular}{c} 5.90 \\ \(\mu\)W/cm\({}^{2}\) \\ \end{tabular} & [65] \\ \cline{3-8}  & & & Nanoribbons &
\begin{tabular}{c} Sputtering/dry transfer \\ \end{tabular} & - & 0.25 & 40 nA & - & [66] \\ \hline \multirow{3}{*}{3.} & \multirow{2}{*}{BaTiO\({}_{3}\)} & Nanotubes & Hydrothermal & 200 \({}^{\circ}\)C & 5.5 & 350 nA & - & [70] \\ \cline{3-8}  & & Nanowire & Hydrothermal & 200 \({}^{\circ}\)C & 7.0 & 360 nA & - & [71] \\ \cline{3-8}  & & \multirow{2}{*}{Nanopillar} & Nanoprimiting process & 60 \({}^{\circ}\)C & 13.2 & 0.33 \(\mu\)A/cm\({}^{2}\) & - & [72] \\ \cline{3-8}  & & & Solid State reaction & 800 \({}^{\circ}\)C & 22 & 140 nA & - & [74] \\ \cline{3-8}
4. & & KNN & Nanorods & Hydrothermal & 160 \({}^{\circ}\)C & 17 & 0.522 \(\mu\)A & 9.135 \(\mu\)W & [75] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._results in the improved piezoelectric performance of the device. In the case of I-, the ionic radius is much larger than that of the oxygen ion, which results in distortion of the lattice structure and decreased piezoelectric performance. For instance, [PERSON] et al. [90] fabricated a PENG based on Br-doped ZnO nanosheets; in their work, ZnO nanosheets were synthesized via the facile hydrothermal method. The fabricated devices generated an output voltage of 8.82 V, which is greater than that of undoped ZnO nanosheets. Br\({}^{-}\) doping reduces the screening effect on the 2D nanosheets, which improves the performance of the fabricated device. Recently, [PERSON] et al. [91] fabricated a piezoelectric sensor based on Er-doped ZnO. In their work, they compared the performance of ZnO, Er-doped ZnO, Er-doped GO/ZnO (1:10), and Er-doped GO/ZnO (1:5). The different compositions were synthesized via the wet chemical method. After the successful fabrication of the materials, they analyzed their performance which was as follows: (70 V, 1.85 \(\upmu\)A/cm \({}^{2}\)), (80 V, 2.16 \(\upmu\)A/cm\({}^{2}\)), and (100 V, 2.47 \(\upmu\)A/cm \({}^{2}\)) for Er-doped ZnO, Er-doped GO/ZnO (1:10), and Er-doped GO/ZnO (1:5) nanocomposite-based NGs, respectively, under a periodic force of 0.21 kgf. (II) BTO  
The piezoelectric performance of BTO can also be improved by selecting an appropriate dopant. Dopants, such as zirconium (Zr) [92] and tin (Sn) [93], can enhance the performance of BTO-based piezoelectric devices. Carbon-containing compounds are used as dopants to maintain a uniform distribution of BTO nanoparticles in polymers such as PDMS and PVDF. In one study, BTO was doped with Zr; thus, the piezoelectric coefficient improved. Further, the Ti\({}^{4+}\) ions were replaced with Zr\({}^{4+}\) ions with smaller ionic radii, thus creating lattice distortion. The TiO\({}_{6}\) octahedron of Zr-doped BTO doubled the piezoelectric performance compared with undoped BTO. Moreover, the peak-to-peak voltage and current of Zr doped BTO were observed to be 11.9 V and 1.35 \(\upmu\)A, respectively, which was more significant than undoped BTO (1.01 \(\upmu\)A) [94]. Another example is Sn\({}^{-}\) and Ca\({}^{-}\)-doped PENGs.