October 2014: SunShot Initiative Supports Group to Develop Hybrid Perovskite Tandem Solar Cells
The Next Generation Photovoltaics 3 Program, which is part of the U.S. Department of Energy SunShot Initiative, supports the Hillhouse Group to explore the chemistry of high bandgap hybrid perovskites and develop novel tandem solar cells that utilize a hybrid perovskite as the top cell. Hillhouse and group member Ian Braly have patented unique tandem device architectures that may allow these solar cells to reach 30% efficiency. See the UW news article here.
October 2014: Andrew Collord's article on combinatorial exploration of native point defects in CZTS to appear in the IEEE Journal of Photovoltaics
We report the systematic investigation of native point defect chemistry in Cu2ZnSn(S,Se)4 and the effects of selected extrinsic dopants by spray coating films from DMSO-thiourea inks in an upcoming issue of the IEEE Journal of Photovoltaics. Over 6,000 unique compositions of Cu2ZnSn(S,Se)4 have been analyzed along with the effects of Cd, Fe, and Na doping. The most likely SRH-active defects appear to be defects and defect clusters involving SnZn, CuSn, and SnCu antisite defects, particularly the cluster [2CuZn + SnZn]. However, it is important to note that we observe high quasi-Fermi level splitting (QFLS) relative to the theoretical limit. In several regions, the ratio QFLS/QFLS,SQ is 0.69. This is higher than the ratio of the measured open circuit voltage to theoretical limit observed even in the record 12.6% efficient CZTSSe devices from hydrazine reported by IBM, which is 0.57. This suggests that the Voc still has significant room for improvement, even without changes to the material itself. While this is very positive, there is still a gap with respect to high efficiency devices from other materials. For instance the ratio of the measured Voc to theoretical Voc in 28.8% GaAs devices, 25.0% c-Si devices, 20.4% CIGSe devices, and 19.6% CdTe devices are 0.96, 0.80, 0.82, and 0.75, respectively.
October 2014: John Katahara's article on semiconductor photoluminescence to appear in the J. Applied Physics
A good photovoltaic material will also be a good radiative emitter. This may seem counter-intuitive at first since radiative recombination of excited carriers is a loss mechanism. However, the mechanism is always present, and it tends to be the slowest recombination pathway. Thus, if you turn off all the faster recombination pathways, you observe the photoluminescence. As a result, the magnitude and spectral character of the photoluminescence can reveal a lot about the inherent material quality and potential device performance. However, in many PV materials, even GaAs, sub bandgap states (Urbach tails and other phenomena) alter the spectral distribution of luminescence. This has hindered previous efforts to accurately extract the quasi-Fermi level splitting or reveal the character of the sub-bandgap states in materials like CIGS and CZTS. In an article to appear in the Journal of Applied Physics, we develop a new and general model of direct bandgap semiconductor absorption coefficients. We then use this model with a corrected Lasher-Stern-Wurfel equation (referred to as a non-equilibrium Planck emission law by some) to model photoluminescence. We validate the model and show a tremendous range of applicability to model PL data from GaAs, CIGS, and CZTS. We use the model to extract the quasi-Fermi level splitting and characterize the sub-bandgap "tail" states. The quasi-Fermi level splitting matches exactly to the measured open circuit voltage in devices fabricated from the materials.
October 2014: Austin Miner Wins the WRF Fellowship
Austin Miner was one of only ~7 undergraduate students from the entire state who received the Washington Research Foundation Fellowship.
The scholarship awards Austin $6000 to conduct research over the next three quarters. In the group, Austin has set-up an instrument that can map the photocurrent across a solar cell down to resolutions of 500 nm using two different excitation wavelengths. He is using this technique, called LBIC, to study copper zinc tin sulfoselenide (CZTS) solar cells.
September 2014: Ian Braly Wins Best Poster at ORCAS for Hybrid Perovskites
Ian Braly won best poster this year at the International Conference on Energy Conversion and Storage (ORCAS). Ian reported the results of combinatorial experiments to develop high bandgap hybrid perovksite photovoltaic materials. Well done Ian!
April 2014: UW Seniors Design a Plant to Manufacture CZTS Ink
What if we mass produced CZTS solar cells from the inks developed in the Hillhouse lab? How much will the ink cost? How much energy will it take to create the precursor chemicals? What are the waste products? Are there health and environmental risks? To help answer these questions, senior undergraduate chemical engineering students have designed the manufacturing plants to create the ink precursors as their capstone design project. The team is studying how the manufacturing plants could impact the surrounding environment and determine if there are better ways to process the materials. The researchers in this project are adding to previous research and developing the big picture of how the technology can be sustainable, healthy for people and the environment, and economically viable. Read more here.
Volunteers from the Hillhouse Group went out to the Pacific Science Center at the Seattle Center for a fun weekend of science education. Graduate students Ian Braly, John Katahara, and Wesley Williamson engaged children of all ages on matters related to solar energy, energy production, energy and resource conservation, as well as general scientific principles. Paws-On-Science weekend is an annual event.
April 2014: Dr. Alexander Uhl Joins the Group
The Group welcomes Dr. Alexander Uhl as a Postdoctoral Research Associate. Dr. Uhl received his Ph.D. in Material Science from the ETH in Zurich Switzerland in 2013 after completing his Diploma degree in Nanostructural Engineering from the University of Würzburg in Germany. He has over 6 years of experience in photovoltaics having worked with Prof. Marika Edoff and Prof. Ayodhya Tiwari on non-vacuum deposition of semiconductor layers. With financial support from the Swiss National Science Foundation (Project P2EZP2_152168), Dr. Uhl is now conducting his postdoctoral research at the University of Washington with the Hillhouse Group.
January 2014: Clean Energy Institute Awards Exploratory Fellowship
Both Andrew Collord and Ian Braly have won Exploratory Fellowships from the newly launched UW Clean Energy Institute. They will both
receive funding for the next two quarters to pursue high-risk high-reward research projects
Governor Jay Inslee toured the Hillhouse lab to help launch the newly founded UW Clean Energy Institute. For more information see the UW CEI news page.
December 2013: Austin Miner Wins the Mary Gates Fellowship
Austin Miner has been awarded the Mary Gates Research Scholarship.
The scholarship awards a $4000 award to Austin over two quarters.
August 2013: Dr. Selin Tosun Joins the Group
Dr. Tosun received her first B.S. degree in Chemical Engineering from Istanbul Technical University in 2007. She earned a second B.S. in Materials Science and Engineering, also from Istanbul Technical University (2008). She joined Prof. Eray S. Aydil's group at the University of Minnesota for her PhD in Chemical Engineering. She worked on CIGS and CZTS based solar cells and related materials. After her graduation in June 2013, she joined Prof. Hugh W. Hillhouse's group at the University of Washington to pursue her career on Thin Film Photovoltaics as a Post-Doctoral Research Associate.
Several of our students joined other research groups from the University of Washington at Shoreline Community College for the NW Solar Fest 2013. Group members Ian Braly, Austin Minor, John Katahara, and Wesley Williamson joined other educators in teaching the public what a solar powered future could look like.
July 2013: Dr. Xin wins best poster
Dr. Hao Xin won best poster at the 2013 IEEE PVSC conference for her work entitled "8.3% Efficient Cu2ZnSn(S,Se)4 Solar Cells Processed from Environmentally Benign Solvent". Congratulations Hao!
The U.S. National Science Foundation has awarded PI Hillhouse and co-PIs Alison Cullen, Daniel Gamelin, Christine Luscombe, and Xiaodong Xu a $1.9M grant to explore a "Sustainable Pathway to Terawatt-Scale Solution-Processed Solar Cells from Earth Abundant Elements." For more information see the NSF Press Release and the UW ChemE news page.
Solar Fest is an annual event that brings together exhibitors, educators, and the public in a festival like environment with food, live music, and plenty of demonstrations. This year there were over 109 exhibitors at Solar Fest. The event is organized by the Shoreline Solar Project for the purpose of promoting the practical application of renewal energy and environmentally responsible practices to enhance the economic, ecological, and social environment of our community. This year Research Group members Cori Bucherl and John Katahara help teach folks about solar energy and what may be possible in the near future.
June 2012: Hillhouse Group Moves into Beautiful New Digs
The Hillhouse Group moves into the brand new Molecular Engineering & Sciences (MolES) building. Other research groups that are also part of the new UW Molecular Engineering & Sciences Institute will be moving in throughout the summer. The entire first floor is dedicated to solar energy research and is home to the Advanced Materials for Energy Institute. The expansive basement is the new home to the Nanotechnology User Facility (NTUF) and has additional instrumentation space.
March 2012: M.J. Murdock Charitable Trust Award
The M.J. Murdock Charitable Trust was created from the estate of Jack Murdock, co-founder of Tektronix. The Trust supports education, scientific research, and enrichment programs in the Pacific Northwest. The Trust awarded Hillhouse and UW colleagues an infrastructure grant to build a unique suite of solar energy materials deposition and characterization instruments.
January 2012: New Group Members
The Group welcomes Dr. Hao Xin and John Katahara. Dr. Xin joins the group as an Acting Instructor with a background in organic solar cells. John Katahara joins the group from Brown University after a summer research experience at the University of Tokyo with Prof. Tatsuya Okubo.
Nanowerk.com features a news highlight focusing on research from Wooseok Ki on a new solution-processing method to form copper zinc tin sulfoselenide solar cells using non-toxic environmentally benign solvents. The full journal article appears in Advanced Energy Materials. Link to Wooseok's article.
September 2011: SunShot Initiative Award
The U.S. Department of Energy SunShot Initiative, whose goal is to develop solar cells that cost just $0.50 per watt, supports the Hillhouse Group with an award. With these funds the Hillhouse group will develop and use combinatorial methods with nanocrystals and molecular precursors to explore the defect chemistry and develop better copper zinc tin sulfoselenide solar cells made with novel inorganic inks.
The American Chemical Society reports that group member Grayson Ford's article is one of the Top 10 Most Read Articles in the journal Chemistry of Materials during the second quarter of 2011. The article reports the discovery that germanium may be used to effectively tune the bandgap of CZTSSe solar cells without degrading the optoelectronic quality of the material. This important phenomenon may let researchers create graded bandgap devices and reach higher efficiencies. Two other UW faculty have articles in the Top 10 list, Prof. Alex Jen and Prof. Sam Jenekhe, both related to solar energy materials. What does it mean? UW faculty are having a major impact on materials development to harness the power of the Sun. Link to Grayson's article.
April 2011: Outstanding Young Alumni Award
Clemson University selects Prof. Hillhouse for their Outstanding Young Alumni Award for his contributions to research in energy conversion. Hillhouse will be presented with the award at the banquet on April 28 in Clemson, SC. Hillhouse graduated with a B.S. in Chemical Engineering from Clemson in 1995.
January 2011: Hillhouse Lab Moves to Seattle
Group members pack-up the lab equipment and hand it over to the movers. After a brief separation and a few replacement purchases, researchers and equipment are reunited in Seattle, and the lab is back up and running.
Phys.org highlights the recent JACS article by group member Qijie Guo on the development of copper zinc tin sulfide nanocrystal-ink based solar cells that are 7.2% efficient at converting sunlight into electricity. Link to Qijie's article.
National Geographic posts a new article titled "Shining Light on the Cost of Solar Energy." The piece pulls together thoughts from Prof. Hillhouse and researchers from GE, NREL, and several other institutions to understand the cost of solar energy.
Research Corporation for Science Advancement (RCSA) selects Hillhouse for the inaugural class of awardees of their Scialog Fellowship on Solar Energy Conversion. The award provides unrestricted funds for the Fellows to pursue high-risk high-reward ideas that may lead to breakthroughs in the conversion of solar energy into electricity or fuels.
August 2010: University of Washington
After 8 wonderful years in the School of Chemical Engineering at Purdue University, Hillhouse accepts the Harry A. & Metta R. Rehnberg Endowed Chair Professorship at the University of Washington. The Rehnberg Chair was created in 1979 with a gift from Metta Rehnberg and was the first endowed professorship in Engineering at the University of Washington. While sadly leaving many good friends and colleagues at Purdue, he joins the ChemE Department at UW where he worked under Prof. John Berg 15 years ago. See the ChemE Departmental news item.