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Students postdocs and scientists receive outstanding training

Students postdocs and scientists receive outstanding training

Students, postdocs, & scientists in CISSEM experience outstanding training. photo by Jim Bosch, NREL

Kippelen plastic solar cell

Kippelen plastic solar cell

From left to right, Jaewon Shim, Professor Bernard Kippelen, Canek Fuentes-Hernandez, and Yinhua Zhou (first author on the Science article) from Georgia Tech, displaying a completely plastic solar cell.
Photo credit: Georgia Institute of Technology

GT graduate student in clean room

GT graduate student in clean room

photo credit: Yongjin Kim, Georgia Tech

Publications collage

Publications collage

An important goal for CISSEM is to facilitate highly visible and wide-spread dissemination of the results of our interfacial research.

Arizona graduate student working in the lab

Arizona graduate student working in the lab

photo by davidsandersphotos.com

Anne Lemon and Raj Giridhagopal CISSEM Alumni

Anne Lemon and Raj Giridhagopal CISSEM Alumni

Read Dr. Anne Simon’s profile                                      Read Dr. Rajiv Giridharagopal’s profile

News & Updates

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Dr. Rajiv Giridharagopal earned his Ph.D. from Rice University, later training as a postdoc with CISSEM in the Ginger research group at the University of Washington. His primary postdoc task was in scanning probe development with application to organic photovoltaic (OPV) studies. He developed fast free time-resolved electrostatic force microscopy (FF-trEFM) and applied that to studying OPV devices, and he collaborated with CISSEM researchers in the Armstrong group at the University of Arizona on OPV scanning probe work. CISSEM’s unique collaborative training culture has been instrumental to his success in his current work as an Optical Probing Tool Development Engineer at Intel. To quote Dr. Giridharagopal “Particularly in a position like mine that has to interact with a wide range of groups of highly disparate backgrounds, just being able to talk to others on the same level is important. In CISSEM I had to do that a lot – much of my FF-trEFM project was somewhat esoteric signal processing, but translating that language (Hilbert Transforms) into a different language (in situ measurements of OPV device performance) is a useful skill. Working in the Center was highly important in that it let me directly interact with a broad range of excellent individuals of varying educational backgrounds. It is hard to understate how important it is to get an outside perspective.” Dr. Giridharagopal’s final piece of advice to current and incoming CISSEM members is to use the inherently cross-institutional nature of CISSEM to help build a personal network.


Collaborative research funded as part of CISSEM at The University of Arizona (Monti), Georgia Tech (BrĂ©das, Kippelen) and NREL (Berry, Ginley) integrates experiments and theory to study a prototypical perylene acceptor (PTCDI)/zinc oxide (ZnO) interface. We show how the types of defects at or near the ZnO surface critically impact its interfacial energy-level alignment with PTCDI, and the appearance of a new interface state inside the ZnO band gap. By combining density functional theory with ultraviolet and X-ray photoelectron spectroscopies, we successfully predicted and observed the interfacial gap states that arise from ZnO-to-PTCDI partial charge transfer; caused by interstitial-zinc defects near the ZnO layer surface. Such gap states can play a key role in charge harvesting or injection at metal-oxide electrodes in organic electronic applications. Our findings highlight the overriding importance of explicitly considering defects to achieve a fundamental understanding of energy-level alignment at heterojunctions between conductive metal oxides and organic semiconductors. Deliberate control of near-surface defects and interfacial gap states could ultimately lead to a useful tool for ‘engineering’ the electronic properties of hybrid interfaces.

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Collaborative research funded as part of CISSEM at NREL (Olson, Ginley) and Princeton University (Kahn) has focused on the energetics and performance of tunable magnesium-doped zinc oxide (MgZnO) interlayers deposited from solution by sol-gel for electron harvesting. Our MgZnO interlayers were characterized in bulk heterojunction (BHJ) inverted organic photovoltaic solar cells (OPVs) based on poly(3-hexylthiophene) blended with the fullerene compounds [6,6]-phenyl-C61-butyric acid methyl ester or indene-C60-bisadduct. By combining photoelectron and photoemission spectroscopies, and device measurements, we have determined that ten percent cationic substitution of zinc by magnesium creates excellent sol-gel MgZnO electron-collecting interlayers; superior to traditional zinc oxide. Our spectroscopy data reveal the bandgap in MgZnO increases due to a downshift in the valence band maximum of the metal oxide, which is in contrast to prior assumptions for MgZnO. The substantially improved open-circuit voltage and fill factor realized by OPV devices with our sol-gel MgZnO interlayer suggest that the substitution of zinc by magnesium reduces charge recombination at the metal oxide/BHJ interface under illumination, and translate to an increased overall efficiency for these devices.

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Message From The Director

Neal Armstrong and CISSEM map

Welcome to the Center for Interface Science: Solar Electric Materials.  We are an EFRC established in 2009, funded by the U.S. Department of Energy, Office of ScienceOffice of Basic Energy Sciences which contribute to our nation’s development of economical, terawatt-level solar energy sources for the 21st century. CISSEM is comprised of a great team of scientists, engineers, and staff located at major universities and research centers in Arizona, Colorado, Georgia, New Jersey, and Washington. An integral part of our mission is to inspire, recruit, and train future energy scientists and leaders in the basic science of solar electric energy conversion.  Our research is focused on the basic science underpinning the development of thin-film photovoltaic energy conversion technologies by understanding and controlling the electronic properties of critical regions called “interfaces” on nanometer length scales.  The chemical composition and energetics of these interfaces significantly affect the overall efficiency and lifetime of solar cells.

Neal R. Armstrong



Center for Interface Science: Solar Electric Materials, an Energy Frontier Research Center
funded by the U.S. Department of Energy, Office of Basic Energy Sciences,
under Award Number DE-SC0001084
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