Tuning output of ZnO piezoelectric nanogenerators through V-doping and SiO2 interlayer

Abstract In recent years, ZnO based piezoelectric nanogenerators (PENGs) have gained considerable attention for vibration energy harvesting and self-powered applications. This study reports the development and optimization of flexible ZnO based PENGs (ITO/ZnO/Al) through vanadium (V) doping and the insertion of a SiO 2 interlayer. When V concentration was increased to 3% the open-circuit voltage and short-circuit current of the PENG increased from ~0.9 V/0.1 μA to 2.2 V/0.3 μA. However, further increasing the V doping to 5% reduced the output to ~1.9 V/0.2 μA. X-ray photoelectron spectroscopy (XPS) analysis showed that at low to moderate V doping levels (1%-3%), the V 5+ /V 3+ ratio increases, leading to enhanced internal polarization and, consequently, an improved piezoelectric output performance. At higher V doping levels (5%), excess vanadium introduces structural defects in ZnO, increasing oxygen vacancies and thereby deteriorating the output performance of the PENG. A 100 nm SiO 2 interlayer was inserted between the 3% V-doped ZnO (VZO) and the Al electrode which introduces a conduction band offset of ~6.4 eV as evaluated from band offset studies. This band offset effectively reduces the leakage current in VZO piezoelectric layer and enhanced the output to ~4.4 V/0.6 μA. The optimized PENG generated an instantaneous power density of ~0.1 μW/cm 2 with normalized power density per unit force and frequency ~8.3 × 10 -4 μW·cm 2 /(N·Hz) which was successfully powered commercial capacitors (1 μF to 10 μF), stopwatch LCD screen and LEDs. This work highlights the role of vanadium states, oxygen vacancies and SiO 2 interlayer in tuning ZnO based PENG performance and demonstrates its potential for powering micro/nanoelectronic devices in self-powered applications.