Lightweight flexible self-powered photo-supercapacitors with good stability through photoelectrochemical deposition of tellurium on PPy–V2O5 films as a new visible light active dual photoelectrode†

Abstract

In this research, electrodeposition and photo-electrodeposition methods have been used to prepare some tellurium (Te)/polypyrrole (PPy)–vanadium oxide (V₂O₅) multi-layer films on flexible indium tin oxide electrodes, as photo-responsive supercapacitor electrodes. Tellurium, which is the major light-absorbing part, has a narrow bandgap well matching the visible light wavelength. However, PPy–V₂O₅ is bifunctional and acts in both photoelectric conversion and energy storage. Taking advantage of the synergetic effect of the corresponding components, Te@PPy–V₂O₅ shows high specific capacitances of 532 and 302 mF cm⁻² at 2.0 and 2.8 mA cm⁻² current densities, respectively, in a neutral electrolyte. In addition, areal capacitance has been measured in the dark and under light illumination. The areal capacitance of the Te@PPy–V₂O₅ electrode increases from 412 to 532 mF cm⁻² under light irradiation at 2.0 mA cm⁻², which is 3.5, 3.7, and 4.1 times larger than the corresponding values for PPy–V₂O₅, Te–V₂O₅, and Te–PPy electrodes, respectively, under identical conditions. This indicates the considerable enhancement of light-induced capacitance. Furthermore, the charge generation and storage mechanism under light irradiation have been verified by phototransient response and open-circuit potential measurements. The Te@PPy–V₂O₅ electrode shows the highest photocurrent and photovoltage, which shows its outstanding photosensitivity. Contributions by diffusion and non-diffusion-controlled capacitance have been calculated and the results have been discussed considering different sweep rate ranges. A flexible photoresponsive symmetrical supercapacitor based on Te@PPy–V₂O₅ electrodes and a PVA–LiCl polymer gel electrolyte have been prepared to study the enhancement of the capacitance under visible light illumination. Areal-specific capacitances of 131 and 45 mF cm⁻² were shown by this flexible solid-state photosupercapacitor (FSSPC) at 1.0 and 3.0 mA cm⁻² current densities, respectively. This indicates great capacitance gain under light illumination (65% at 3.0 mA cm⁻² current density) and superior retention of capacitance (93% over 12 000 cycles). High capacitance retention and specific capacitance are shown by the FSSPC device, which is suitable for different bending angles in a wide range of temperatures from −10 to 50 °C. The favorable capacitance retention (∼98%) in the bending mode of this electrode in bendable devices makes Te@PPy–V₂O₅ promising for photo-chargeable smart devices.