Due to the intermittent nature of solar energy availability, often an energy storage element such as a battery or supercapacitor is required to store the energy from a solar cell. The combination of a separate solar cell and an energy storage device is not usually suitable for small and compact electronic circuits with small footprints. Although various hybrid solar cell-supercapacitor devices have been studied before, the majority of them are two cells in one package with one electrode being shared between the two cells. We have designed and studied a new class of two-terminal hybrid electrochemical cells made of conducting polymer (e.g., polyaniline) composites with porous electrodes. In one design, a polymer film with embedded dye molecules has been used as a photoactive electrode in a supercapacitor presenting open circuit voltage changes up to 430 mV under illumination. In another design, the conducting polymer was employed in the electrolyte of the cell making a supercapacitor with the capability of harvesting light through the electrolyte. Voltages as high as 138 mV were achieved in the new device. Due to the storage property, the voltage drop 10 min after the secession of light was ~15 mV. While the fabrication of devices with the photoactive gel is easier, the higher efficiency in thin-film devices is more promising. Further development of two-terminal hybrid cells can open doors for designing compact and self-powered wireless sensors for various applications, including wearable electronics.
In recent years, the interest in photovoltaic supercapacitors has been increasing in order to develop self-powered sensors for a sustainable system. Hence, significant research efforts are needed to enhance the photoelectric and electrochemical performances of hybrid devices. Herein, we have studied the effect of the porosity of different counter electrodes on the performance of the hybrid photovoltaic supercapacitors. The photovoltaic supercapacitors were fabricated in one package with a simple structure including a titanium dioxide (TiO2) coated on fluorine-doped tin oxide (FTO) glass as a working electrode and polyaniline (PANI)-based gel electrolyte. The performance of the hybrid device was studied with four different counter electrodes: a multi-walled carbon nanotube (MWCNT) porous electrode, PEDOT:PSS coated on FTO glass, carbon monolithic electrode, and a carbon-based conductive fabric. The specific capacitance of the device with PEDOT:PSS coated FTO electrode was 255 mF/g in the dark and increased to be 274 mF/g under the light based on the mass of the gel. The hybrid device can be charged when the working electrode is illuminated. The variation in the open circuit voltage (DV) was reached 256 mV in 400 s under illumination, and the voltage drop was 4 mV (−4%) in 600 s of the dark. The current results of the hybrid photovoltaic supercapacitor, with a simple fabrication process and basic structure, are boosting the study for the electrode materials selection to enhance the performance of the hybrid device.
The integration of energy-harvesting and storage in a single device is considered to be one of the most demanding technologies for future wireless sensors. Photovoltaic supercapacitors are among promising solutions with the dual properties of photoelectric and electrochemical charge storage. In order to improve the efficiency in hybrid photovoltaic supercapacitors, most research has focused on studying electrode materials. In this work, we have studied the effect of polyaniline (PANI) concentration in a composite gel-based electrolyte on the impedance of the device. The photovoltaic supercapacitors were fabricated in a two-electrode configuration combining a titanium dioxide (TiO2) coated on fluorine-doped tin oxide (FTO) glass as the working electrode, a multi-walled carbon nanotube (MWCNT) porous electrode as the counter electrode, and a composite gel-based electrolyte. The composite gel was made of polyvinyl alcohol (PVA), hydrochloric acid (HCl), ammonium persulfate (APS), and different concentrations of aniline (ANI). The impedance study of the gel with 0.5 mM concentration of PANI showed a two-stage charge storage mechanism associated to the double-layer at the electrode-electrolyte interface and a pseudo-capacitive charge storage mechanism in the bulk of the electrolyte. The absorption spectrum of the synthesized gel shows a strong absorption peak near 780 nm confirming the formation of the emeraldine salt of PANI in the gel. The current results are inspiring the research for optimizing the composite material to improve both energy harvesting and the charge storage stability in photovoltaic supercapacitors.
Dye sensitized solar cells (DSSCs) are electrochemical solar cells depending on dye molecules that absorbing the radiation and start generating the photoelectrons. DSSCs are the most harmonious device among the other types of solar cells to be coupled with the energy storage devices such as pseudocapacitors to make a solar-capacitor device because of their electrochemical nature. Pseudocapacitors are electrochemical devices that can store charges through the double layer structure and changing the oxidation state of conducting polymer materials (i.e. Polypyrrole, Ppy). The effect of adding methylene blue dye molecules (MB) to the solar capacitor device was absorbed in the previous work by recording the voltage of the composite materials Ppy+MB under the effect of illumination by 23 ∆mV. In this work, TiO2 as electron transport layer (ETL) was added to the anode electrode to facilitate the movement of photo generated electrons. The results of solar-capacitor device exhibited 570 ∆mV open circuit voltage under the effect of light condition in 400 s. The short circuit current results showed a 2 uA under the light condition. The presented results are hopeful to enhance the performance of solar energy and charge storage devices.
In the past few years, with the advance of laser technology, laser engraving has been considered as an alternative method to traditional lithography in the fabrication of microfluidic devices. Considering solution-based method as the main technique for perovskite deposition, the capillary motion of perovskite precursor can be employed for filling a laser-engraved patterned conducting layer. Herein, we used CO2 laser micromachining for the fabrication of the perovskite photodetector. First, several microchannels were formed by laser engraving of indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. Power, speed and frequency parameters of the laser were varied in order to achieve the desired channel roughness. The samples were characterized by scanning electron microscope (SEM) and potentiostat. The I-V characteristics and bode plots of the sample showed a capacitive and an inductive behavior. Finally, a simulation tool was used to analyze the experimental data. This approach offers a simple, rapid and low-cost fabrication method for perovskite photodetector and can be used in large-scale commercial application.
Integrating both electrochemical solar cells (harvesting energy) and supercapacitors (energy storage) into a single device is unquestionably one of the great challenges nowadays. There has been an extended research in the design and construction of integrated solar energy harvesting and storage systems that can simultaneously capture and store various forms of energies from nature. Here, we successfully designed, fabricated and characterized a compact and monolithically photoelectrochemical device combining a polyvinyl alcohol (PVA)/hydrochloric acid (HCl)- based gel electrolyte, multi-walled carbon nanotube (MWCNTs), and fluorine doped tin oxide (FTO) as counter and working electrodes, respectively. The combination device can act either as an independent solar cell, a supercapacitor, or as a solar cell/supercapacitor device. In this structure, energy harvesting takes place only at the working electrode (WE) that made of a thin film composite of a conducting polymer (i.e. Polyaniline, PANI) and synthetic dyes materials that coat on the FTO surface by electrochemical deposition technique. The energy storage occurs in both WE and counter electrode (CE) that made of (MWCNTs) in addition to the gel electrolyte materials. Different synthetic dyes have been used such as Methylene Blue (MB), Methyl Orange (MO), and Prussian Blue (PB). Among them, MB has shown the strongest photoelectrochemical reaction in HCl-PVA gel electrolyte. The cyclic voltammetry was used to show the effect of PANI/synthetic dyes on the cell, and impedance spectroscopy demonstrated the effect of surface modification of MWCNTs on the performance of the CE.
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