A Photophysical Study of Electronic Transfer from Battery Active Materials to an Organic Dye: Towards Developing an Operating Photobattery

Abstract

Intensive efforts are currently dedicated towards developing devices that can convert and store renewable energy that is 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. The also have the benefit of mitigating 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 to 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 a high energy density along with 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 focused on developing a single device that can collectively harvest the sun light energy and store it 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, its role as a photoactive layer has not been experimentally validated. 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 the required electron transfer from the lithium active compound of the battery upon photoexcitation was therefore evaluated. Systematic studies of both steady-state and time-resolved emission quenching measurements will be presented. These will be complemented with transient absorption spectroscopy measurements. It will then be presented that the spectroscopic studies provide sound evidence for electron transfer between the constitutional “solar” and “battery” components, laying the experimental groundwork for an all-in-one photobattery. Step-wise electrochemical studies such as galvanostatic cycling in the presence of the dye using various photo-cathode architectures, and post-cycling chemical analyses on the different photoactive and battery components will also be presented. The photophysical and electrochemical studies will provide sound evidence that both the photoactive and batteries technologies can be successfully merged. It will further be presented that conventional solvents in batteries can be replaced with environmentally benign water. The combined aqueous photobattery is expected to have a positive ecological impact both in terms of using sustainable means for energy harvesting/storage and the constitution components used for assembling the device.