Synergistic integration of energy harvesters and supercapacitors for enhanced performance

In this paper, it is integrated a piezoelectric energy harvester and a supercapacitor storage device on a flexible substrate with a connection through an innovative alternative current (AC) to direct current (DC) boosting power management system for wearable biosensors' power supply. Flexible substrates can conform to irregular surfaces or shapes, enabling energy harvesting and storage devices to be integrated into a variety of form factors, including curved or bendable surfaces. Having an integrated energy harvester and storage system ensures a reliable and portable power source, providing power autonomy. The proposed element was layer-by-layer design including silver electrode, polyvinylidene fluoride-trifluoroethylene/multiwall carbon nanotubes, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate: carbon nanotubes, aluminium oxide, graphene and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate: carbon nanotubes (Ag/PVDF-TrFE:MWCNT/PEDOT:PSS:CNT/Al₂O₃/Gr/PEDOT:PSS:CNT), prepared by spray coating. A voltage rectifier with a low-pass filter and a direct current to direct current (DC-DC) converter was used as a power management system and intermediate unit between the harvester and storage part of the element. The type of the electronic circuit is voltage-doubler rectifier. It was found that piezoelectric harvester can generates voltage with a magnitude of 2V at loading of 110 g/cm²@10 Hz and with the proposed electronic circuit can be determined the workability of the created element during repeated charging and discharging, without introducing interfering changes in the capacity. The behaviour of the supercapacitor part is dependent on the thickness of Al₂O₃ and demonstrates more favourable characteristics at the thicker film of 750 nm, where the charging time is short (6s), the voltage ripples are small (±0.50 mV), and the maximum output voltage after charging almost reached the input supply voltage (∼1.94 V output voltage at 2 V input voltage). In addition, it resists up to 15500 cycles and shows a stable retention capacitance of 1.63 mF. The devices retain their capacity at multiple bending (1000) to 93 % and 91 %, according to the aluminium oxide film thickness, which is suitable for wearable devices.