Photovoltaically Self-Charging Battery

Abstract

For many low-power applications, solar cells are used as an environmentally friendly power supply. In order to provide electrical power also in the absence of solar radiation, we invented a device which unifies both a solar cell and a rechargeable battery in one unit. The main components are a photoactive layer on a charge-storage layer. Thus, this new device represents a flat battery, which charges itself on illumination. In principle it can be produced cheaply, e.g., by screen printing. The characteristics of charging and discharging are presented with special consideration of the variation of light intensity and ion concentration in the electrolyte. A relatively high reverse reaction at the WO 3 electrode still takes place. After charging for 1 h under an illumination of 1000 W/m 2 , the first samples yielded 1.8 C/cm 2 when discharged in the dark.The dye-sensitized solar cell represents an electrochemical solar cell in which an organic dye is excited by illumination with light and transfers an electron from a redox couple in an electrolyte ͑I Ϫ /I 3 Ϫ in an organic solvent͒ to a highly porous TiO 2 layer. 1 By this, the energy of the electron is increased and this energy can be used to supply an external load. The electrons are re-injected into the I Ϫ /I 3 Ϫ couple in the electrolyte via a catalyst like Pt. This dye sensitized solar cell already contains most of the components of a battery, one redox couple (I Ϫ /I 3 Ϫ ), an electrolyte ͑mostly an organic solvent͒, and two electrodes ͑TiO 2 and Pt͒. To complete the battery, only a second redox couple is needed. TiO 2 is usually not sufficient, because its reduction potential for Li ϩ intercalation is too high, as can be concluded from Ref. 2. The charge capacity of a typical dyesensitized solar cell is measured in Ref. 3 to be about 20 C/ cm 2 , which is due to surface adsorption phenomena. In this paper, we present the idea to add a second redox couple in the form of an additional layer (WO 3 ), which is able to store the energy generated by the solar cell. The reduction potential for Li ϩ -intercalation of WO 3 is close to 0 V vs. standard hydrogen electrode, 4 and therefore it is suitable for the potentials in a dye-sensitized solar cell, where the reodox potential of the I Ϫ /I 3 Ϫ couple is about 0.53 V vs.hydrogen, 5 and the open-circuit potentials of the dye-sensitized TiO 2 layer vs. the I Ϫ /I 3 Ϫ couple on the Pt electrode are about 0.7 V. 6The design of the photovoltaically self-charging battery ͑PSB͒ is shown in Fig. 1. It consists of a photoactive layer ͑dye-coated nanocrystalline TiO 2 ͒ which is situated on a charge-storage layer ͑e.g., nanocrystalline WO 3 ͒ on a glass substrate coated with a transparent conductive oxide ͑TCO͒. The opposing electrode is a platinized, TCO-coated glass substrate. The Pt layer is so thin that it is still transparent. The pores of the WO 3 and TiO 2 layers and the space between the two electrodes are filled with an electrolyte which contains Li ϩ and a redox couple ͑I Ϫ and I 3 Ϫ ͒ in an organic solvent ͑e.g.,pro...

Design Considerations for Unconventional Electrochemical Energy Storage Architectures

“…The I 3− /I − has a redox potential of 0.53 V vs. hydrogen and operates through a shuttle effect between both electrodes For example, Hauch et al have designed a WO 3 | LiWO 3 || LiI | LiI 3 cell having a dye-sensitized TiO 2 cell incorporated at the anodic site and a catalytic Pt fi lm at the cathodic site. [ 717 ] Under illumination, the photons absorbed by the photovoltaic layer generated an electron-hole pair triggering a redox reaction at the shared electrode as well as in the electrolyte: 3I − / I 3− -WO 3 mobility. The cell delivered 1.8 C cm −2 in dark after being illuminated at 1000 W m −2 for 1 h. Other photorechargeable cells based on I − /I 3− redox-electrolytes have been explored making use of polypyrrole redox electrodes, [ 718 ] CNT-polyaniline composite electrodes, [ 719 ] symmetric activated carbon, [ 720,721 ] TiO 2 /poly(3,4-ethylenedioxythiophene)-polypyrrole polymeric storage electrodes, [ 722 ] poly (3,4-ethylenedioxythiophene), [ 723 ] and poly (3,3- [ 724 ] supercapacitor electrodes, interdigitated comb-like electrodes, [ 725 ] electrocatalytic mesh supported TiN nanotube arrays [ 726 ] as well as for the realization of LIB-solar cells power pack, [ 727 ] integrated energy wires, [ 274,728 ] as well as hybrid harvest-store-sense devices.…”

Dye-Sensitized Solar Cells

“…Several types of DSSC systems have been reported that combine DSSC with other solar cells in tandem structures [118] or the ones with an additional charge storage layer [119][120][121]. In the later, the sol-gel chemistry in the preparation of their components is necessary; therefore the emphasis of this section is on hybrid DSSC systems with additional charge storage (Fig.…”

“…Hybrid DSSC systems implement the device with chromogenic properties resulting in photoelectrochomic smart windows [119,120] or allow the storage of the electrical energy produced by solar cell (solar-charging battery) [121]. In both systems tungsten oxide (WO 3 ) has been studied as a charge storage layer and lithium ions (Li + ) were incorporated into the electrolyte in order to maintain the charge balance of the systems during coloration/charging and bleaching/discharging processes (Eq.…”

Light Energy Conversion and Storage with Soft Carbonaceous Materials that Solidify Mesoscopic Electrochemical Interfaces

“…In this respect, efforts have been made to combine a photovoltaic electrode and redox-active materials for rechargeable reactions. [43][44][45] Repeated oxidations and reductions, however, shorten the lifetime of the cell. The capacitor is a more desirable tool for its long lifetime due to redox-free electrolytes and for rapid response to current change (light variation).…”