# Presentation: 805163

## Time-Resolved Electrostatic Force Microscopy of Polymer Solar Cells

**Time-Resolved Electrostatic Force Microscopy**** of Polymer Solar Cells**

**Height**

**Charging Rate**

**arb. units**

**Faster**

**Slower**

- D. C. Coffey and D. S. Ginger, Nature Materials, 2006, doi:10.1038/nmat1712

- Time-resolved electrostatic force microscopy allows direct mapping of variations
-   in local charging rates when donor/acceptor polymer blends are illuminated
-  These maps help us understand how these photovoltaic blends operate—identifying
-   regions of loss, and pointing to ways to improve efficiency

- DMR-0449422

**Notes:**
We have introduced a new method—time resolved electrostatic force microscopy—to help understand how nanostructured excitonic solar cells operate.  We have applied this method to a model donor/acceptor polymer blend system.  Not only can the local measurements successfully predict the performance of a final bulk solar cell, but the results were surprising in suggesting that in some cases, mesoscale domain interfaces showed slower photoinduced charging than the bulk phases—we attribute this to differences in local composition and molecular scale mixing of the donor/acceptor polymers within each domain.

From left to right: (left) Schematic of the experimental approach: The polymer blend, cast on a transparent conducting electrode, is illuminated from below, while an electrostatic force microscope tip is used to measure the rate of charge accumulation at the film surface in point-by-point fashion.  (mid) Atomic Force Microscopy topography image of a donor/acceptor polymer blend (right) corresponding charging rate image, showing fastest charge generation at the domain centers

This work has been published online in Nature Materials: doi:10.1038/nmat1712  and is tentatively scheduled for print publication in the Sept 2006 issue

Future Plans:
We are applying this technique to learn more about other efficient and widely-studied polymer blends (such as MDMO-PPV/C60)
We are measuring carrier recombination rates as a function of local morphology
We are developing new conducting AFM methods to measure photocurrent with even higher resolution
We are applying similar EFM and CAFM techniques combined with single-molecule spectroscopy to semiconductor nanocrystal quantum dot samples to better understand blinking phenomena and the operation of hybrid quantum-dot LEDs

## NSF Broader Impacts

**David Ginger, Dept. of Chemistry, University of Washington, Seattle, WA**

**Technological and Societal:**

-  Reducing fossil fuel use and dependence on foreign oil is one of the most
-   important challenges facing society today
-  An enhanced microscopic understanding of polymer solar cell performance
-   bottlenecks in nanostructured photovoltaic blends will help us design better
-   nanostructured solar cells

**Educational:**

-  “Student Seminars in Nanoscience” Course at UW—undergraduate and
- graduate students from chemistry, physics, materials science, bioengineering, and
- communication presented interdisciplinary topics—improving cross-disciplinary
- understanding of nanoscience topics among students, and student abilities to
- communicate about science
-  Graduate Student Andrea Munro won a cash prize for her development of
- nanoscience outreach materials for high school students concerning quantum dots
-  Developed new computer-based modules for teaching undergraduate quantum
- chemistry

- DMR-0449422

**Notes:**
Educational: 

1)  This class has been a popular way for students to brush up on their presentation skills, and has become a venue for me to actively teach public speaking skills.  Students have used it to rehearse everything from conference talks, to their thesis defense, to demonstrations they are planning to give to middle school students.  Having an audience of fellow grad students from outside their home department quickly helps them realize how much better we all need to communicate across disciplinary boundaries

2) Encouraging graduate students to participate in outreach allows younger students to better see themselves as graduate students—Andrea Murno has been a star in this aspect, in fact we just got another email today from North Seattle Community College: “First let me thank you, Andrea, for the talks you gave at the high school nanotech seminar.  They were very good, they broadened the students understanding and I have also used some of your slides in teaching nano 101 at NSCC”

3) Computer-based modules: many quantum problems are mathematically challenging, in order to increase computer literacy AND allow a wider range of problems to be tackled by the students, I have developed a set of 6 Maple-based worksheets that I use to teach the discussion sections for my honors quantum chemistry sections (which are small enough to hold in a campus computer lab with Maple installed).  This spring I made my first Excel-based worksheet (a simple exercise on the variational theorem that also allowed students to encounter numeric rounding errors).  I plan to develop more Excel-based worksheets in the future and more fully integrate them into the “regular” class sections, which are too large to hold in campus computer labs.  My goal is that by using Excel, I will allow the students to actually edit the calculations on their home computers (rather than simply turn knobs on a web demo) without requiring them to purchase additional software (since Excel is available on almost all students computers).