Interfaces for Solar Energy Conversion
The interest and expertise of the group lie at the intersection of materials and interfaces for solar energy conversion. Our research efforts focus on new understanding of and pathways toward photovoltaics and solar fuels generation with disruptively high power efficiency, large earth-abundance, or low-cost fabrication. While commercial solar energy conversion is growing at an explosive rate, the basic understanding of the surface chemistry and the optoelectronic processes necessary to develop affordable and sustainable solutions to world's energy need has just begun. As such, we aim to ascertain and influence the arrangement of atoms at interfaces, which largely dictate the underlying physics of solar energy conversion devices. Recent studies include the use of atomic layer deposition to grow hematite (the main component in rust) and catalysts for solar fuels production, the stabilization and surface passivation of sulfide-based thin film solar absorbers, and the rational design of multi-gap absorbers for the next generation of photovoltaics.
Shannon Riha (EERE Postdoctoral Fellow)
Stabilizing Cu2S. Copper sulfide, Cu2S, functioned as the solar absorber in one of the first efficient thin film photovoltaics. However, large and uncontrollable electronic doping resulted in limited efficiency and ultimately, to poor solar cell stability. Here, the surface of semiconducting Cu2S films are observed to oxidize in minutes under ambient atmosphere resulting in an orders of magnitude change in conductivity. In order to address these instabilities, Argonne scientists have introduced the atomic layer deposition of a barrier layer to reduce the intrinsic doping and further slow the aging process, even in air. Taken together, these experiments detail a mechanism for the environmentally induced degradation mechanism in Cu2S-based photovoltaics. Furthermore, through preliminary efforts to control oxygen incorporation at the interface, a more stable and efficient Cu2S-based solar cell may be envisioned. Now, the allure of such an ideal solar absorber comprising these highly earth-abundant and non-toxic elements has stimulated new efforts to understand and stabilize the material. (ANL Solar Energy Systems Highlight)
Atomic Layer Deposition of Water Oxidation Catalyst. Earth-abundant semiconductors capable of directly converting sunlight into fuels may provide a singular solution to solar energy conversion and energy storage. Fuels are a particularly attractive form in which to store renewable energy owing to the high energy density and portability of chemical bonds. Argonne researchers, working with collaborators at Michigan State University, have shown that the efficiency of water splitting with hematite - the most prevalent iron oxide in rust - is dramatically enhanced by additional of an ultra-thin cobalt-based coating. Atomic layer deposition was employed to grow a cobalt oxide film of less than one atomic layer that is transparent, stable, and capable of accelerating the rate at which O2 is generated at the semiconductor/water interface. When viewed as a general approach to accelerating the photoelectrochemical conversion of sunlight to fuels this methods paves the way for improvement of a wide variety of catalytically-limited solar fuels reactions. (ANL Solar Energy Systems Highlight)
Low-Temperature Iron Oxides. Iron oxides are a family of nontoxic, earth-abundant materials with a variety of oxidation states and stoichiometries that exhibit a plethora of useful electronic and magnetic properties. However, targeting a specific stoichiometry from a family of materials is challenging for ALD and requires careful design of the molecular precursor. An additional challenge for the ALD of specific iron oxide targets is low-temperature deposition. Until now, there has been no report on the direct deposition of crystalline iron oxide (Fe3O4 or α-Fe2O3) below 180 °C without postdeposition annealing. Low-temperature deposition routes are appealing for many of the applications pertaining to the iron oxide family, especially where the need for flexible and thermally sensitive supports/substrates is paramount. We report a low-temperature (T = 120 °C) route to conformal deposition of crystalline Fe3O4 or α-Fe2O3 thin films determined by the choice of oxygen source selected for the second surface half-reaction. We utilized this process to prepare conformal iron oxide thin films on a porous framework, for which α-Fe2O3 is active for photocatalytic water splitting. (publication link)
Martinson and Pellin are 2 of 25 principal investigators in a large collaborative research program conducted through the Argonne Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Pellin further serves the Center as Deputy Director. Funding has also been provided by the U.S. Department of Energy, Energy Efficiency and Renewable Energy Office through the SunShot Program. Publications with US and international universities including Northwestern University, Michigan State University, and Universitat Jaume I de Castelló have resulted from fruitful collaborations in recent years.
Postdoctoral Positions - No funded positions are currently available. However, positions are always available for exception candidates with the possibility of thier own support. For example, current and prior postdocs have received funding through the highly competitve EERE SunShot Fellowship and ANL Director's Postdoctoral Fellowship.
Undergraduate Research Positions - Summer internships are available through the Science Undergraduate Laboratory Internships (SULI) Program. Highly motivated students with interest in solar energy technology at the sub-nanometer scale are encouraged to apply.