Abstract
The nature of solar radiation is not steady, therefore having a solar-capacitor device that can simultaneously capture, convert and store solar energy is a considerable device. A self-charging capacitor is designed and fabricated as a functional solar energy storage device, which is accomplished in situ self-assembled storage technique. The solar-capacitor device is assembled on a multilayered photoelectrode combining different concentration of cationic dye (i.e. methylene blue, MB) and conducting polymer (i.e. polyaniline, PANI) in contact with H2SO4-Polyvinyl alcohol (PVA) gel electrolyte. The mechanism of storage the photo-generated charges takes place at the changing of redox oxidation states. Due to the high porosity of the multi-walled carbon nanotube (MWCNT) based counter electrode and PANI at the working electrode the device is working as photocapacitor. But, because of the presence of MB molecules that embed in the PANI can absorb the light and excite the electron from the highest occupied molecular orbital (HOMO) level to the lowest unoccupied molecular orbital (LUMO) level. Therefore, the supercapacitor can be charged when the working electrode is illuminated. In this study, a photo-electrochemical device based on two-terminals that combines H2SO4-PVA, MWCNT, and fluorine doped tin oxide conductive substrate (FTO) as working electrode is successfully designed and fabricated. This device can work independently as solar cell, supercapacitor, or a solar-capacitor device. Different concentrations of the cationic dye, MB, composite with PANI have been used as a thin film coated electrochemically on the surface of the FTO. The experiments are carried out in the dark at the beginning and then repeated when the working electrode is under the effect of solar irradiation. After illumination, the experiments repeat in dark again to see the effect of the light on the performance of the device. When the device is exposed to the light, the redox oxidation peaks of PANI/MB change. This clearly shows the photo-electrochemical reaction of the PANI/MB. The open circuit voltage across the cell in the dark is 0.92 mV. Then, the cell voltage is increased gradually from 0.92 mV to 4.9 mV in 400 s of illumination. After turning off the light, the voltage is dropped to the dark value immediately. The results of electrochemical and electrical characterization techniques such as Cyclic Voltammetery (CV), Electrochemical Impedance Spectroscopy (EIS), Open Circuit Voltage (OSV), and Short Circuit Current (SCC) on the solar-capacitor device have been addressed in this study. The results are encouraging for application of PANI/dye composite film for solar-capacitor devices to harvest solar energy and store charges in a single device with two-terminals.
Figure 1