Fluorescence and Electrochemistry to Study the Electronic Transfer from an Organic Dye to Battery Active Materials: Towards Developing an Operating Photobattery
Authors: Briqueleur Elsa , Dollé Mickael , Skene William 
Published: May 2020

Intensive efforts are currently dedicated towards developing devices that can convert and store renewable energy derived from renewable sources. These are to address the current global energy consumption needs and reduce the carbon footprint that is associated with the use of primary non-renewable energy resources. Indeed, many of these approaches are promising for reducing energy inequalities. They can also mitigate greenhouse emissions. Within this context, solar energy is among one of the best suited candidates to address the global energy needs in a sustainable manner. It is also an attractive energy source because of its widespread availability. A major challenge of using solar energy is that it must be stored for use during periods when there is no sun. Devices are therefore required that can convert, store, and deliver the stored energy during dark periods.

To address the energy storage needs, lithium-ion batteries have been successfully coupled to solar cells such as silica based photovoltaic panels. Indeed, lithium-ion batteries are suitable candidates because they are a proven technology that offers high energy density and a long cycle life. Furthermore, they are ideal for portable applications such as photobatteries. These are energy capturing and storage devices that combine a light harvesting solar cell with an energy storing battery. The collective efforts of our research groups have been focused on developing a single device that can collectively harvest the energy derived from sun light and store its energy courtesy of redox reactions that are specific to a battery. Our approach involves merging dye-sensitized solar cell technology (DSSC) with a proven lithium ion battery to ultimately make an all-in-one device. Towards this end, we investigated an organic dye as the light harvesting component. The given dye was selected because it satisfies many of the physical and electrochemical requirements for its use in the combined photobattery. Of importance, is the dye’s photophysical properties. It broadly absorbs in the visible spectrum, it is capable of being reduced by the battery’s electroactive component upon light absorption, it exhibits a high degree of colorfast, and it is photostable.

While the organic dye in principle possesses the required properties that are suited for its use as the light harvesting component of the photobattery, these have not been experimentally validated under. Both the photophysical and electrochemical properties of the dye under device-like conditions must therefore be evaluated. To confirm the concept, the capacity of the organic dye to undergo required electron transfer from the lithium active compound of the battery upon photoexcitation was therefore evaluated. Studies done by both steady-state and time-resolved emission quenching measurements in a systematic way will be presented. These will be complemented with transient absorption spectroscopy measurements. These were done to confirm that the desired dye radical anion was indeed formed by electron transfer from the lithium active component. Step-wise electrochemical studies such as galvanostatic cycling and chroroamperometry under illumination, with the various photoactive and battery components, will also be presented as evidence for the required light mediated electron transfer mechanism. It will be presented that collectively the individual photo- and electrochemical studies provide sound evidence for electron transfer between the constitutional “solar” and “battery” components, laying the experimental groundwork for an all-in-one photobattery. It will further be presented that conventional solvents in batteries can be replaced with environmentally benign water. The combined aqueous photobattery will therefore have a positive ecological impact both in terms of using sustainable means for energy harvesting/storage and the constitution components of the device.