December 2015: Ian Braly's paper on effect of composition on optoelectronic quality in hybrid perovskites to appear in The Journal of Physical Chemistry C.
We have reported the effect of composition on optoelectronic quality and stability of hybrid perovskites in an upcoming issue of The Journal of Physical Chemistry C. By using a combinatorial spray coating apparatus, we explored thousands of compositions of hybrid perovskites, ranging from MAPbI3 to MAPBI2Br. Absolute Intensity Photoluminescence (AIPL) mapping was then used to determine the quasi-Fermi level splitting (QFLS) at each composition. We have found that QFLS increases as expected with band gap, reaching a maximum of 1.27 eV for Eg = 1.75 eV. Comparing the QFLS to the maximum theoretical QFLS at each Eg, we have determined that the optoelectronic quality decreases with band gap from 88% (Eg = 1.60 eV) to 82% (Eg = 1.84 eV). Link to Ian's article.
December 2015: Dr. Alex Uhl's paper on solution-processed CIS and CIGS to appear in Energy and Environmental Science.
We have reported record efficiency solution-processed CIS in an upcoming issue of Energy and Environmental Science. We have used benign solvent solution processes to achieve a CIS solar cell with 13.0% PCE. Careful exploration of the redox chemistry has identified high thiourea to metal ratios as leading to the best devices. Our optimized processing yields devices with Vocs (507 mV) close to those of state-of-the-art vacuum-processed absorbers (515 mV and 491 mV). This work marks a high-water mark for non-toxic solution processed CIS. Link to Alex's article.
September 2015: Jac Clark Wins 1st Place Poster Prize in 8th Annual UW Chemical Engineering Graduate Student Symposium
Jac won the 1st Place Poster Prize in 8th Annual UW Chemical Engineering Graduate Student Symposium for his poster titled "Cu2ZnSn(S,Se)4 Solar Cells from Inks: Combinatorial Screening and High Efficiency Device Fabrication". Congratulations Jac!
September 2015: John Katahara Wins 2nd Place Oral Presentation Prize in 8th Annual UW Chemical Engineering Graduate Student Symposium
John was awarded 2nd place in the oral presentation division of the 8th annual UW Chemical Engineering Graduate Student Symposium. He presented on his work "Illuminating the Potential of Solar Cells." The talk was well received by the audience, which included numerous professional attendees from local companies like Boeing and the Fred Hutchinson Cancer Research Center. He was described by one audience member as the "Bob Ross of PV". Congratulations John!
September 2015: Dr. Alex Uhl Wins Best Poster Prize at EU-PVSC 2015
Dr. Alex Uhl won best poster prize at the 2015 EU-PVSC for his work entitled "Molecular-ink Route to 13.0% Efficient Low-bandgap CuIn(S,Se)2 and 14.7% Efficient Cu(In,Ga)(S,Se)2 Solar Cells". Congratulations, Alex!
August 2015: Dr. Hao Xin's and Sarah Vorpahl's article on lithium-doping of CZTSSe to appear in Physical Chemistry Chemical Physics.
We have reported on the effect of Li-doping at the grain boundaries (GB) of CZTSSe in an upcoming issue of Physical Chemistry Chemical Physics. We show that Li inverts the electric field at grain boundaries in solution-processed CZTSSe, resulting in pushing the minority carriers away from the GB. Repelling the minority carriers effectively passivates the grain boundaries, allowing us to achieve devices with a non-hydrazine, solution-processed record of 11.8% PCE. Possible mechanisms are formation of LiCu, which reduces the concentration of less favorable ZnCu defects, and formation of LiZn defects, which are shallower than CuZn. Link to Hao's and Sarah's article.
June 2015: Dr. B. Selin Tosun's article on vapor-equilibrated regrowth (VERG) of triiodide hybrid perovskites to appear in The Journal of Physical Chemistry Letters.
We report the improvement of crystallinity and optoelectronic quality of methylammonium lead triiodide (MAPbI3) hybrid perovskites via VERG in an upcoming issue of The Journal of Physical Chemistry Letters. Solution processed planar films of MAPbI3 are often of poor quality - poor surface coverage, small grains, and large numbers of defects. We have developed a novel post-deposition treatment to correct morphology and optoelectronic quality. Treatment of films results in a large improvement in minority carrier lifetime, improving from 10 ns to over 200 ns. Link to Selin's article.
June 2015: Andrew Collord's article on impact of nanocrystal reaction time on nanocrystal CSTSSe solar cells to appear in Solar Energy Materials and Solar Cells.
We report the effect of CZTS nanocrystal reaction time on CZTSSe solar cells in an upcoming issue of Solar Energy Materials and Solar Cells. Longer reaction times yield nanocrystal with larger size and more compositional uniformity. This translates into devices with improved performance - better current collection, higher Voc, and higher efficiency. The larger grains also reduce the number of grain boundaries, limiting potential non-radiative recombination sites. Link to Andrew's article.
June 2015: Trevor Martin's article on ligand-free CdS nanoparticle synthesis to appear in Chemical Communications.
Our report of ligand-free CdS nanoparticles made in a sulfur copolymer matrix will be published in an upcoming issue of Chemical Communications. We have developed a procedure to synthesize CdS nanoparticles using a sulfur copolymer. The copolymer is simultaneously the S source and solvent, yielding ligand-free CdS nanoparticles. This allows us to avoid needing to remove any ligands before the CdS can be used. Link to Trevor's article.
April 2015: Paws-On-Science at Pacific Science Center
John Katahara and Wesley Williamson joined other members of the UW Clean Energy Institute for the annual Paws-On-Science weekend at Pacific Science Center. These UW researchers fielded questions from members of the Puget Sound community on topics ranging from solar cells to next-generation batteries, as well as what Washington is doing with clean energy generation. Children were able to explore some of these concepts first-hand by building and racing solar cars.
March 2015: Bryant Elementary School 4th/5th Grade Science Fair
Graduate students John Katahara, Jac Clark and undergraduate student Austin Miner volunteered their time in March for the 2015 Bryant Elementary School Science Fair. Over the course of 9 weeks, these members of the Hillhouse Group joined other researchers from UW in mentoring 4th/5th graders on basics of conducting scientific research. The science fair is an annual event.
February 2015: Andrew Collord's article on the temporal evolution of CZTS and CZTGS nanocrystals synthesis to appear in Chemistry of Materials.
We report the effects of reaction time on composition of kesterite nanocrystals synthesized by hot-injection in an upcoming issue of Chemistry of Materials. We have determined that short reaction times result in nanocrystal inks with large size and composition heterogeneity. Increasing reaction time narrows the size and stoichiometric variation, yielding inks with compositions near that of the starting precursors. We have also found that the choice of starting metal reagent only has a minor role in determining final ink composition. We can leverage this knowledge to produce kesterite nanocrystal inks with our desired off-stoichiometric compositions. Link to Andrew's article.
November 2014: Hillhouse-Ginger Lab article on surface potential variation in solution processed CZTSSe to appear in Nano Letters
The results of a Hillhouse-Ginger Lab collaboration correlating nanoscale surface potential in solution-processed CZTSSe with local S/Se ratio is reported in an upcoming issue of Nano Letters. We have used scanning Kelvin probe microscopy (SPKM) to correlate local surface potential of CZTSSe films with local stoichometry from EDS. We have found that S-rich regions have more negative surface potentials, implying an increase in acceptor-like defect density. Link to article.
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. Link to Andrew's article.
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. Link to John's article.
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.