National Science Foundation     |     Directorate for Engineering  (ENG)
Division of Chemical, Bioengineering, Environmental, & Transport Systems  (CBET)
CBET Award Achievements 
Notable Accomplishments from CBET Awards
Engineers Overcome Processing Challenges
to Produce More Efficient Solar Cells

Kenneth K.S. Lau  -  Drexel UniversityPhiladelphia, Pennsylvania

Simplified Description

Outcome:  Lau and his team at Drexel University in Pennsylvania have synthesized polymers (plastics) in an entirely liquid-free and environmentally green process that can be used to produce more efficient solar cells for converting sunlight into electricity.

Impact/Benefits:  Using plastic materials in the fabrication process could lead to cheaper and more flexible solar cells, making it easier to adopt this sustainable technology.  Introducing materials processing methods that don't use toxic liquid solvents also minimizes the impact on the environment.

Background/Explanation:  Solar cells that rely on a photosensitive dye to absorb sunlight currently use a liquid electrolyte (a liquid that conducts charges) as part of the cell assembly.  By replacing the liquid electrolyte with a polymer electrolyte (a solid containing long chain molecules that conducts charges) would make the cells more robust and eliminate any leakage.  However, solar cells with polymers are currently constructed using liquid processing methods that are not effective in creating efficient cells.
Lau's liquid-free processing technique for making polymers overcomes liquid processing problems and enables more efficient cells to be made in a more environmentally friendly way that eliminates any use of toxic liquids.  Lau's research is engaging engineers from underrepresented groups, including women and African Americans, and providing opportunities for high school students to participate in science projects.  In addition, Lau plans to establish solar testing stations in Philadelphia area high schools to evaluate solar cell shelf life, and create unique experiences for learning science and engineering.

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Detailed Engineering Description

Background:  A dye sensitized solar cell (DSSC) is a solar cell that uses a photosensitizer dye to absorb sunlight and convert solar energy to more practical electrical energy.  As part of the DSSC makeup, a liquid electrolyte is used to conduct charges within the cell.  However, a liquid electrolyte is prone to leakage and severely limits how the DSSC can be deployed.  Replacing it with a solid polymer electrolyte that can perform the same function as the liquid electrolyte would be a significant step forward.  However, current ways to construct the DSSC with polymers utilize liquid processing methods that interfere with how much polymer can be effectively built into the solar cell as a result of wettability issues.  This leads to reduced solar cell efficiency.  Thus, a more effective polymer processing strategy is critical for making the DSSC a viable solar cell technology.

Results: Lau and his research team at Drexel University in Philadelphia, Pennsylvania have developed a novel liquid-free processing method that overcomes current liquid processing challenges and enables the effective use of polymer materials in constructing more efficient solar cells.  By not using any liquid solvent during polymer processing, wettability issues are eliminated and the process is more environmentally friendly.  DSSCs made using this processing technology have shown higher efficiencies.  These results are recently published in the scientific journal Nano Letters.

Kenneth K.S. Lau Image   Figure 1.  Scanning electron microscope images of a polymer electrolyte effectively built into a solar cell using Lau's liquid-free and environmentally green process.  The polymer is able to completely fill into the nanoscale pore spaces of the solar cell construct that leads to higher cell efficiency.
Image Credit:  Kenneth K.S. Lau;  Drexel University
Scientific Uniqueness:  The liquid-free processing method is known as initiated chemical vapor deposition (iCVD).  This is a novel one step process for chemically synthesizing and physically growing polymers within solar cell constructs.  By tuning both the rate of polymer synthesis (kinetics) and the rate of reactant delivery (transport), the proper amount of polymer can be integrated within DSSC constructs for maximizing solar cell efficiency.

This project addresses the NSF Strategic Outcome Goals, as described in the NSF Strategic Plan 2006-2011, as follows:
- 1 Primary Strategic Outcome Goal:       (1) Discovery:  A liquid-free polymer processing method, initiated chemical vapor deposition (iCVD), has been developed that effectively integrates polymer electrolytes within dye sensitized solar cells that lead to higher efficiencies.
- 2 Secondary Strategic Outcome Goal:  (2) Learning:  Engineers from underrepresented groups, including women and African Americans, are being trained.  High school students are being engaged in science projects.  Science and engineering concepts stemming from the research have enhanced undergraduate and graduate curriculum.
- 3 Additional Strategic Outcome Goal:   (3) Research Infrastructure:  The novel iCVD processing technology is available as a more general technique for liquid-free processing of polymers resulting in collaborations with academic peers at Drexel University and the University of Pennsylvania in Philadelphia, Pennsylvania, and with companies, including GVD Corporation and Syngenta Corporation.

This Award Achievement represents potentially Transformative Research:  The research is potentially transformative as a new technique has been developed that overcomes current processing challenges and creates polymer-based solar cells that achieve higher efficiencies.  Introducing polymers in solar cell technologies could potentially reduce cost and lead to flexible cells that can be deployed in a wider range of options than are currently available.

The Intellectual Merit of this project is the ability to utilize the iCVD processing technology requires fundamental understanding of reaction kinetics and mass transport during polymer synthesis and growth.  With a liquid-free environment, these processes are not well understood and research in this area will enable effective polymer processing and application in a wide range of fields.

The Broader Impacts of this activity include:
- 1Benefits to society:  Facilitating polymer integration in solar cells could lead to more robust, flexible, and efficient cells that could ultimately lead to more widespread adoption of solar energy as a sustainable energy resource. Utilizing a liquid-free processing technique could reduce the impact of toxic liquid solvents on the environment.
- 2Broadening participation of underrepresented groups:  A woman and African American engineers are currently being engaged in research.  High school students, including the disabled, have been involved with science projects related to the research.
- 3Advancing discovery and understanding while promoting teaching, training, and learning:  The research has enabled significant gains in the understanding of liquid-free synthesis and growth of polymers as well as the role of polymers in solar cell operations.  This has led to a major publication in Nano Letters.  In addition, the research involves the training of two Ph.D. graduate students, one being an African American woman, as well as several undergraduate and high school students.  The new science and engineering concepts from the research have been incorporated into undergraduate and graduate curriculum.
- 4Enhancing the infrastructure for research and education, such as facilities, instrumentation, networks, and partnerships:  The research has established a state-of-the-art liquid-free polymer processing system which has promoted collaborations with researchers at Drexel University and the University of Philadelphia in Philadelphia, Pennsylvania in extending the solar cell research.  In addition, the processing facility has attracted companies in utilizing the technology in applications outside of solar cells.  Solar cell testing stations are planned for installation in Philadelphia area high schools to enhance the understanding of alternative energies and to practically test solar cell life times.
- 5Results disseminated broadly to enhance scientific and technological understanding:  The research has been presented at major conferences, including meetings of the Materials Research Society, American Vacuum Society, American Institute of Chemical Engineers, and the Electrochemical Society.  In addition, the work has been presented at international conferences, including the International Conference on Hot Wire Chemical Vapor Deposition and EuroCVD meeting.  Publications have been made in scientific journals, including Nano Letters, Thin Solid Films, ECS Transactions, and the MRS Proceedings.

Program Director:
Maria Burka
CBET Program Director - Process and Reaction Engineering
NSF Award Number:   0846245
Award Title:   CAREER: Engineering and Integration of Polymer Electronic Materials for Alternative Energies
PI Name:   Kenneth K.S. Lau
Institution Name:   Drexel University
Program Element Code:   1403
CBET Award Achievement:

  FY 2011

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This Award Achievement was Updated on 23 March 2011.