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Highlights: [•] High quality thin film of multiferroic BiFeO3 on SrRuO3 is grown by RF Sputtering. [•] The Pt/BFO/SRO structure showed diode like behavior through I–V measurement. [•] Appreciable VOC and JSC were observed with illumination of white light. [•] The photoresponse at zero bias of BFO film showed rapid increase in photocurrent. [•] Application of BFO film for photosensitive capacitor is demonstrated. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerators (PENG), which convert random mechanical energy into electrical energy, have attracted considerable attention due to their application potential in self-powered micro and nano electronics devices, wearable electronics, sensors etc. PENGs based on ZnO nanostructures are particularly important due to their low cost, flexibility and bio-compatibility. Flexible PENGs based on ZnO nanostructures dispersed in Polydimethylsiloxane (PDMS) in ITO/ZnO:PDMS/ITO device configuration were fabricated and characterized for vibration energy harvesting applications. Surfactant free ZnO nanostructures were grown using co-precipitation route and ZnO:PDMS nano-composite films with ZnO content varying in the range of 1.5–7.5 wt% were deposited on ITO/PET substrates for PENG fabrication. The maximum open circuit voltage and short circuit current of ~ 2.5 V and ~ 4 µA respectively were obtained in PENG fabricated with 6 wt% ZnO. The output characteristics were further enhanced to 5 V and 6 µA with flowing oxygen ambient annealing of ZnO nanostructures generating an instantaneous power density of ~9.55 µWcm−2. X-ray photoelectron spectroscopy studies confirmed reduction in oxygen vacancy and enhancement in oxygen interstitial concentrations on oxygen annealing which leads to the suppression of free carrier induced internal screening in ZnO nanostructures. This suppression of internal screening effect is the possible reason for the enhancement in output characteristics of ZnO:PDMS PENG fabricated with oxygen annealed ZnO nanostructures. The electrical energy generated by the ZnO:PDMS PENG was rectified and effectively stored in capacitors and used to power LEDs and LCD display. • ZnO nanostructures were grown by co-precipitation method with air and oxygen annealing. • ZnO:PDMS PENG with variable wt% of ZnO in PDMS were fabricated in ITO/ZnO:PDMS/ITO configuration. • The output performance of ZnO:PDMS PENG is improved significantly by annealing ZnO nanostructures in flowing oxygen ambient. • XPS established a correlation between the oxygen related point defects in ZnO and output characteristics of ZnO based PENG. • The output energy from ZnO:PDMS PENG was rectified and effectively stored in capacitor to flash LEDs and LCD display. [ABSTRACT FROM AUTHOR]

The increasing demand of energy harvesting and wearable electronics applications requires the development of flexible and highly durable piezoelectric nanogenerators (PENG). In this work, We have fabricated flexible ZnO:PVDF based PENGs for vibrational energy harvesting and shoe insole pedometer application s. ZnO nanorods were grown by hydrothermal method and incorporated into PVDF matrixes in the concentration range of 5–15 wt%. These homogeneous ZnO:PVDF composite films were sandwiched between Al electrodes to realize flexible free standing PENGs. The open circuit voltage (Voc), short circuit current (Isc) and instantaneous power density of PENGs increased from ∼ 4 V, 0.4 µA and 1.6 µW/cm2 to ∼ 14.6 V, 0.6 µA and 21.3 µW/cm2 respectively when ZnO nanorods concentration in PVDF increased from 0 to 10 wt% and decreased with further increase in ZnO nanorods concentration. The enhancement in output characteristics of ZnO:PVDF PENG with increasing ZnO concentration was attributed to β-phase crystallization of PVDF, which was confirmed by XRD and FTIR measurements. The deterioration in output characteristics beyond 10 wt% of ZnO nanorods concentration was explained considering the variation of dielectric constant and remnant polarization. The rectified output of the PENGs was effectively stored in various commercially available capacitors and used to power LEDs and stopwatch displays. The PENG with 10 wt% ZnO concentration was used to develop shoe insole pedometer which was interfaced with android based mobile application via Bluetooth. The shoe insole pedometer was successfully tested for 5000 steps at different walking frequencies ranging from 0.5 Hz to 2 Hz in the speed range of ∼ 1.4 km/h to 5.5 km/h. This study not only gives an insight into the mechanism of ZnO:PVDF based PENGs but also opens up their potential in vibration energy harvesting and shoe insole pedometer applications. • ZnO:PVDF based flexible piezoelectric nanogenerators (PENGs) were fabricated with variable ZnO nanofiller concentrations. • The variation of output performance of ZnO:PVDF based PENGs was studied with ZnO nanofiller concentrations. • The PENGs were able to power capacitors, LEDs, and LCDs. • A pedometer device has been fabricated using the ZnO:PVDF based flexible PENG sensor. [ABSTRACT FROM AUTHOR]