Grantee Research Project Results
Final Report: Don’t Eat Your Spinach: Nature Inspired Biohybrid Solar Cells
EPA Grant Number: SU836022Title: Don’t Eat Your Spinach: Nature Inspired Biohybrid Solar Cells
Investigators: Jennings, G. Kane , Anilkumar, Amrutur V. , Dilbone, Eric , Ingram, Philip , Locke, Trevan , McDonald, Paul , Ogg, Jason
Institution: Vanderbilt University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2011 through August 14, 2012
Project Amount: $14,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2011) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Air Quality , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities
Objective:
The development of a secure energy future requires unique approaches to classical problems. Recent work has sparked interest in the development of solar cells that utilize the largest solar energy conversion process on the planet, photosynthesis, as a means of producing electrical energy. The lab of Dr. Kane Jennings of the Department of Chemical and Biomolecular Engineering at Vanderbilt University has developed a method for employing Photosystem I (PSI), a photoactive protein present in plants and some bacteria, in solar cells. When assembled onto a working electrode as a film, PSI absorbs light to trigger a flow of electrons from the underlying electrode that can be captured by mediator molecules in solution and routed to a transparent counter electrode to produce a photocurrent that can power simple devices. We aim to build on these results to construct novel, large-scale, biohybrid solar panels for power production. This task presents a number of unique challenges to be addressed:
- Determine the best materials to allow affordable mass production of individual solar cells.
- Optimize the electrolyte/mediator solution to increase the individual cell performance.
- Investigate alternative packaging options to promote long-term durability.
- Overcome issues associated with connecting a large number of cells to form a large panel.
- Deploy the panel outdoors and measure the solar conversion voltage and current output, as well as the overall efficiency, using direct solar irradiation over a period of a month.
As an end product, our team aims to construct a solar panel consisting of 1-ft by 1-ft modules with each module containing up to 32 individual solar cells. Each individual cell would contain a 1-μm thick film of PSI as the active light-conversion coating in contact with a mediator solution. Quick disconnects on each module will allow the panel to be easily deployed in an outdoor environment. Unlike traditional solar cells, which require the use of rare metals, the most essential component of our device, Photosystem I, is mass produced in abundance by Nature. Overall, the production and use of our Nature-inspired cells poses no threat to the environment and further develops a means for reducing fossil fuel consumption. These cells are straightforward to prepare in a typical lab, and they do not require expensive fabrication facilities or materials. Thus, we envision that this technology, once matured, will become established in developing countries where energy is mostly off grid to reduce energy poverty and increase economic development.
Summary/Accomplishments (Outputs/Outcomes):
Cell Design. After a detailed materials and economic analysis, we have designed individual solar cells as schematically shown in Figure 1. From the bottom up, glass slides were selected as the base substrate due to their inexpense and robustness. Nanoporous gold films were prepared by dealloying gold leaf (a 50:50 Au/Ag alloy priced at 3.5 cents/ cm2) and attaching the 100-nm thick film via a molecular linker to the surface of glass. We selected nanoporous gold due to its high surface area to enable much higher interfacial areas between the electrode and the PSI for electron injection, as compared to a smooth gold film, as well as the electrochemical stability of gold as an electrode and the thinness of the nanoporous film to allow good penetration by light. The PSI film was prepared by first extracting PSI from spinach using a new approach that dramatically boosted our yield over previously published methods. The extracted PSI was deposited onto the nanoporous gold substrate by a vacuum-assisted deposition method developed by the Jennings group to achieve a 1-μm thick PSI film. Within the biohybrid cell, the PSI film is in contact with an electrolyte solution containing mediator molecules that have the ability to both receive and donate electrons to the active sites of PSI to maintain good electron transfer throughout the PSI film. The mediator solution is in contact with a transparent counter electrode, indium tin oxide (ITO), to allow light to enter the cell while maintaining a conductive surface to pull electrons from the reduced mediators. Finally, we are using poly(methylmethacrylate), also known as acrylic, for the sides of the cell. Acrylic is transparent to allow good light penetration into the cell and works much more effectively than poly(dimethylsiloxane) for preventing leaks of the electrolyte solution, as we have observed. Our selection of acrylic will thus lead to much longer cell lifetimes, as water leaks and associated problems are the most common reasons for underperformance of the cells. A photograph of a completed cell (7.5 cm x 3.8 cm) is shown in Figure 2. The copper tape shown in the cell is used to connect individual cells to make the modules. The total materials/supplies cost for the cell is $0.17 per cm2, showing economic viability even at this early stage of development.
Figure 1. Schematic of the Phase I cell design. Light is transmitted through the transparent glass and ITO-coated PET and is absorbed by the Photosystem I film, causing electrons to be pulled from the nanoporous gold electrode and routed to oxidized mediators in solution. The mediators diffuse to the ITO electrode, discharging their electrons, and creating both a light-generated current flow and potential difference.
Figure 2. Photograph of a biohybrid cell.
Cell Testing. We have tested individual cells with artificial white light at an intensity of 95 mW/cm2. Figure 3 shows the photoresponse of a typical cell. Initially, the current is low as the cell is in the dark. This dark current is due to oxidized mediator molecules receiving electrons at the nanoporous gold surface. When the light is turned on, the current increases sharply as the oxidized mediators now can be reduced by activated PSI proteins to increase the number of electrons pulled from the nanoporous electrode and yielding an average photocurrent of 2.6 μA/cm2. When the light is turned off, the photocurrent decreases sharply and falls back near the original “dark current” baseline, which is now at higher current due to the redistribution of oxidized and reduced mediators in the PSI film.
Figure 3. Effect of white light (95 mW/cm2) on the measured current versus time for a biohybrid cell. The average photocurrent density here is 2.6 μA/cm2.
Module Assembly. We are now working to assemble individual cells into 1 ft by 1 ft modules, and individual modules into larger panels. The schematic view of a module is shown in Figure 4, where 32 individual cells are connected in series so that cell potentials add across the module. This assembly work will continue until mid April with field testing of the modules and panels under real solar conditions over the summer months. We will show a 1’ by 1’ module and a few individual cells at the National Sustainable Design Expo in April.
Figure 4. Schematic of a 1’ x 1’ module containing 32 individual cells connected in series.
Conclusions:
We have designed and fabricated biohybrid solar cells where Photosystem I proteins serve as the active light-harvesting components. The cells are straightforward to mass produce by undergraduate students, and the materials have been selected to optimize photocurrent and enhance the longevity of the cells. The individual cells, which cost $0.17 per cm2 to produce, can be connected together in series to create modules with elevated photopotentials. The ease of preparing these truly “green” biohybrid solar panels opens doors for their use in developing countries to combat energy poverty, which would benefit overall societal education and health, as well as boosting local economies by employing regenerable natural resources within the region as key raw materials for sustainable energy
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 1 publications | 1 publications in selected types | All 1 journal articles |
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Beam JC, LeBlanc G, Gizzie EA, Ivanov BL, Needell DR, Shearer MJ, Jennings GK, Lukehart CM, Cliffel DE. Construction of a semiconductor–biological interface for solar energy conversion:p-doped silicon/photosystem I/zinc oxide. Langmuir 2015;31(36):10002-10007. |
SU836022 (Final) SU835287 (Final) |
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Supplemental Keywords:
solar energy, biohybrid, proteins, solar panels, solar cells, Photosystem IP3 Phase II:
Don't Eat Your Spinach: Nature Inspired Biohybrid Solar Cells | 2013 Progress Report | 2014 Progress Report | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.