(Press-News.org) EUGENE, Ore. -- Nov. 20, 2014 -- A potential path to identify imperfections and improve the quality of nanomaterials for use in next-generation solar cells has emerged from a collaboration of University of Oregon and industry researchers.
To increase light-harvesting efficiency of solar cells beyond silicon's limit of about 29 percent, manufacturers have used layers of chemically synthesized semiconductor nanocrystals. Properties of quantum dots that are produced are manipulated by controlling the synthetic process and surface chemical structure.
This process, however, creates imperfections at the surface-forming trap states that limit device performance. Until recently, improvements in production quality have relied on feedback provided by traditional characterization techniques that probe average properties of large numbers of quantum dots.
"We want to use these materials in real devices, but they are not yet optimized," said co-author Christian F. Gervasi, a UO doctoral student.
In their study, detailed in the Journal of Physical Chemistry Letters, researchers investigated electronic states of lead sulfide nanocrystals. By using a specially designed scanning tunneling microscope, researchers created atomic-scale maps of the density of states in individual nanocrystals. This allowed them to pinpoint the energies and localization of charge traps associated with defects in the nanocrystal surface structure that are detrimental to electron propagation.
The microscope was designed in the lab of co-author George V. Nazin, a professor in the UO Department of Chemistry and Biochemistry. Its use was described in a previous paper in the same journal, in which Nazin's lab members were able to visualize the internal structures of electronic waves trapped by external electrostatic charges in carbon nanotubes.
"This technology is really cool," said Peter Palomaki, senior scientist for Voxtel Nanophotonics and co-author on the new paper. "When you really dig down into the science at a very fundamental level, this problem has always been an open-ended question. This paper is just the tip of the iceberg in terms of being able to understand what's going on."
The insight, he said, should help manufacturers tweak their synthesis of nanocrystals used in a variety of electronic devices. Co-author Thomas Allen, also a senior scientist at Voxtel, agreed. The project began after Allen heard Gervasi and Nazin discussing the microscope's capabilities.
"We wanted to see what the microscope could accomplish, and it turns out that it gives us a lot of information about the trap states and the depths of trap states in our quantum dots," said Allen, who joined Voxtel after completing the Industrial Internship Program in the UO's Materials Science Institute. "The information will help us fine-tune the ligand chemistry to make better devices for photovoltaics, detectors and sensors."
The trap states seen by the microscope in this project may explain why nanoparticle-based solar cells have not yet been commercialized, Nazin said.
"Nanoparticles are not always stable. It is a fundamental problem. When you synthesize something at this scale you don't necessarily get the same structure for all of the quantum dots. Working at the atomic scale can produce large variations in the electronic states. Our tool allows us to see these states directly and allow us to provide feedback on the materials."
INFORMATION:
Sony Corp. supported the research. Quantum dots were synthesized by VoxtelNanophotonics, a division of Voxtel Inc., which has research space in the UO's Lorry Lokey Laboratories. The microscope, which was described in a recent paper in the journal Review of Scientific Instruments, was built with funding from the National Science Foundation (grant DMR-0960211).
Co-authors with Gervasi, Allen, Palomaki and Nazin are Dmitry A. Kislitsyn and Jason D. Hackley, both doctoral students, and Ryuichiro Maruyama, a courtesy research associate in the Nanoscale Open Research Initiative of the UO's Department of Chemistry and Biochemistry.
Sources: George Nazin, assistant professor of physical chemistry, Department of Chemistry and Biochemistry, 541-346-2017, gnazin@uoregon.edu; Christian Gervasi, doctoral student, 541-346-8150, cgervasi@uoregon.edu; Peter Palomaki, senior scientist, VoxtelNano, a division of Voxtel Inc., 541-346-8131, peterp@voxtel-inc.com; and Thomas Allen, senior scientist, VoxtelNano, a division of Voxtel Inc., 541-346-8131
Note: The University of Oregon is equipped with an on-campus television studio with a point-of-origin Vyvx connection, which provides broadcast-quality video to networks worldwide via fiber optic network. In addition, there is video access to satellite uplink, and audio access to an ISDN codec for broadcast-quality radio interviews.
Previous release: Special UO microscope captures defects in nanotubes: http://uonews.uoregon.edu/archive/news-release/2014/10/special-uo-microscope-captures-defects-nanotubes
New paper abstract: http://pubs.acs.org/doi/abs/10.1021/jz5019465
About Voxtel: http://voxtel-inc.com/about-voxtel/
Nazin faculty page: http://chemistry.uoregon.edu/profile/gnazin/
Nazin Lab: https://wiki.uoregon.edu/display/Nazin/Nazin+Group
Department of Chemistry and Biochemistry: http://chemistry.uoregon.edu/
About the microscope: http://scitation.aip.org/content/aip/journal/rsi/85/10/10.1063/1.4897139
CHAMPAIGN, Ill. -- The majority of preschoolers may not be getting the amount of sleep they need each night, placing them at higher risk of being overweight or obese within a year, according to a new study.
Published online by the journal Sleep Medicine, the study investigated links between mothers' employment status and their children's weight over time, exploring the impact of potential mediators, such as children's sleep and dietary habits, the amount of time they spent watching TV and family mealtime routines.
"The only factor of the four that we investigated that ...
Washington, DC--Levels of testosterone and other naturally-occurring reproductive hormones play a limited role in driving menopausal women's interest in sex and sexual function, according to a new study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.
While testosterone is the main sex hormone in men, women also have small amounts of it. The ovaries naturally produce testosterone. Researchers set out to examine the role the hormone plays in sexual function as women go through menopause.
"While levels of testosterone and other reproductive ...
Washington, DC--As many as one in five people with Type 2 diabetes do not see any improvement in blood sugar management when they engage in a supervised exercise regimen, according to a new scientific review published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.
People develop Type 2 diabetes when their bodies become resistant to the hormone insulin, which carries sugar from the blood to cells. This leads to excess sugar in the bloodstream. The U.S. Centers for Disease Control and Prevention projects about 40 percent of Americans will develop ...
Enzymes carry out fundamental biological processes such as photosynthesis, nitrogen fixation and respiration, with the help of clusters of metal atoms as "active" sites. But scientists lack basic information about their function because the states thought to be critical to their chemical abilities cannot be experimentally observed.
Now, researchers at Princeton University have reported the first direct observation of the electronic states of iron-sulfur clusters, common to many enzyme active sites. Published on August 31 in the journal Nature Chemistry, the states were ...
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BANGALORE, INDIA (November 20, 2014) - Participation of non-scientists as volunteers in conservation can play a significant role in saving wildlife, finds a new scientific research led by Duke University, USA, in collaboration with Wildlife Conservation Society and Centre for Wildlife Studies, Bengaluru.
The study has shown that citizen science projects greatly contribute to 'increased environmental awareness among the general public'. It also reported direct impacts on conservation including - shift in formal profession by volunteers to become conservationists, initiation ...
Moderate rainfall was occurring around the center of Tropical Storm Adjali before it dissipated, according to data from NASA and the Japan Aerospace Exploration Agency's Global Precipitation Measurement or GPM satellites.
Adjali became the first named storm of the Southwest Indian Ocean 2014/2015 cyclone season when it formed on November 16, 2014. Adjali became a strong tropical storm the next day and just two days later started to dissipate.
The GPM observatory captured data on Adjali's rainfall rates on Nov. 18. GPM's Microwave Imager (GMI) instrument is similar to ...
This new survey was released November 19 as a Web First by Health Affairs. The full text is available free until November 26.
International Survey Of Older Adults Finds Shortcomings In Access, Coordination, And Patient-Centered Care
By Robin Osborn, Donald Moulds, David Squires, Michelle M. Doty, and Chloe Anderson
All authors are affiliated with The Commonwealth Fund in New York.
This study was supported by The Commonwealth Fund and also will appear in the December issue of Health Affairs.
The study surveyed 15,617 adults ages sixty-five and older in Australia, ...
In many firms sales people spend as much time negotiating internally for lower prices as they do interacting with customers. A new study appearing in the November issue of Marketing Science, a publication of the Institute for Operations Research and the Management Sciences (INFORMS) finds that firms should allow their sales people to "waste" energy on internal negotiations. In fact, it says, firms should make the process wasteful on purpose.
The study, "Why do sales people spend so much time lobbying for low prices?" was conducted by Duncan Simester, the Nanyang Technological ...
When blood vessels are damaged through surgery, it can trigger an endless cycle of scarring and repair.
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Ameer, who is also ...
