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Physical Sciences
Research Highlights

August 2015

A New Material for Transparent Electronics

Specialized crystalline films revealed to be highly conductive and transparent

Designer film
Scanning transmission electron micrograph of a p-Sr0.12La0.88CrO3/n-SrTiO3(001) heterojunction. The Sr0.12La0.88CrO3 conducts holes and the SrTiO3 conducts electrons. When particles of sunlight (photons) are absorbed in the material, an electron and a hole are created, and they move to opposite sides of the junction: the electron to the SrTiO3 and the hole to the Sr0.12La0.88CrO3. If the junction is connected to an electrical circuit, the electricity created by the light can be used for electrical power (solar cell application), or to detect the incoming light (photodetector application). zoom Enlarge Image.

Results: The performance of solar cells, flat panel displays, and other electronics are limited by today's materials. A new material, created by modifying a transparent insulating oxide, replacing up to 25 percent of the lanthanum ions in the host material with strontium ions, offers considerable promise. The new perovskite film, with the formula SrxLa1-xCrO3, (x up to 0.25), conducts electricity more effectively than the unmodified oxide and yet retains much of the transparency to visible light exhibited by the pure material.

Why It Matters: Materials that are both electrically conductive and optically transparent are needed for more efficient solar cells, light detectors, and several kinds of electronic devices that are by nature transparent to visible light. Of particular importance are new materials that conduct electricity by using missing electrons, otherwise known as "holes." The new perovskite film falls into this category.

Methods: The development of high-performance transparent conducting oxides (TCOs) is critical to many technologies ranging from flat panel displays to solar cells. Although electron conducting (n-type) TCOs are presently in use in many devices, their hole-conducting (p-type) counterparts have not been commercialized as candidate materials because they exhibit much lower conductivities. Scientists at Pacific Northwest National Laboratory along with collaborators at Binghamton University and the Paul Drude Institute in Berlin show that La1-xSrxCrO3 (LSCO) is a new p-type TCO with considerable potential. The researchers demonstrate that crystalline LSCO films deposited on SrTiO3(001) by molecular beam epitaxy show figures of merit which are highly competitive with best p-type TCOs reported to date, and yet are more stable and structurally compatible with the workhorse materials of oxide electronics, as seen in the image. Being structurally and chemically compatible with other perovskite oxides, perovksite LSCO offers considerable promise in the design of all-perovskite oxide electronics.

Acknowledgments

Sponsors: This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award #10122. The computational work was supported in part by the Pacific Northwest National Laboratory Laboratory Directed Research and Development program. The synchrotron measurements were funded in part by the National Science Foundation under DMR 1409912.

Research Area: Materials Science

User Facilities: The work was performed in EMSL, the Environmental Molecular Sciences Laboratory, a national science user facility sponsored by the Department of Energy Office of Science's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Use of the National Synchrotron Light Source at Brookhaven National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-98CH10886. Beamline X24a, which was used for our measurements, is supported by the National Institute of Standards and Technology.

Research Team: Scott A Chambers, Hongliang Zhang, Yingge Du, Petr Sushko, Mark E Bowden, V Shutthanandan, PNNL; Shawn Sallis and Louis F. J Piper, State University of New York at Binghamton; Liang Qiao, University of Manchester; Guixin Cao and Zheng Gai, Oak Ridge National Laboratory; Alexandra Papadogianni and Oliver Bierwagen, Paul-Drude-Institut fr Festkrperelektronik

References:

Zhang KHL, Y Du, PV Sushko, ME Bowden, V Shutthanandan, S Sallis, LFJ Piper, and SA Chambers. 2015. "Hole-Induced Insulator-to-Metal Transition in La1-xSrxCrO3 Epitaxial Films." Physical Review B 91:155129. DOI: 10.1103/PhysRevB.91.155129

Zhang KHL, Y Du, PV Sushko, ME Bowden, V Shutthanandan, L Qiao, GX Cao, Z Gai, S Sallis, LFJ Piper, and SA Chambers. 2015. "Electronic and Magnetic Properties of Epitaxial Perovskite SrCrO3(001)." Journal of Physics: Condensed Matter 27:245605. DOI: 10.1088/0953-8984/27/24/245605

Zhang K, Y Du, A Papadogianni, O Bierwagen, S Sallis, LFJ Piper, ME Bowden, V Shutthanandan, PV Sushko, and SA Chambers. 2015. "Perovskite Sr-doped LaCrO3 as a New p-type Transparent Conducting Oxide." Advanced Materials27:5191-5195. DOI: 10.1002/adma.201501959


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