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April 09, 2019
A physics master’s degree opens doors to myriad careers
See what our own Ed Caner has to say about his program.
February 21, 2019
The Optical Society of America Highlights Physics’ Faculty
Thermally-Painted Metasurfaces Yield Perfect Light Absorbers for High-Tech Applications
This article highlights the work of Professors Giuseppe Strangi and Michael Hinczewski and grad student, Jonathan Boyd.
October 16, 2018
Physics Department Annual Pumpkin Drop!
21st Annual CWRU Physics Department Pumpkin Drop!
Wednesday October 26th @ 12:30pm
Outside Strosacker Auditorium.
October 11, 2018
Robert Badea Defense
Robert Badea will be defending his thesis on November 2, 2018 at 1:00 p.m. in the Rockefeller Building, Room 301.
His Dissertation Title is: Manipulation of Magnetic Vortex Dynamics Revealed by Optical and Single-spin Microscopy.
Let’s support him on this special day!
May 29, 2018
21st Eastern Gravity Best Student Presentation Winner – Laura Johnson!
The 21st Eastern Gravity Meeting, hosted by Long Island University--Brooklyn, was held Thursday, May 24 and Friday, May 25, 2018 in Brooklyn, NY.
This annual regional meeting is open to researchers of all levels, from undergraduate students to faculty, in all areas of gravitational physics, including classical, quantum, theory, observation, computation and experiment. The purpose of the conference is to encourage the interaction of researchers in the Northeastern region.
We are happy to announce that one of our own, Laura Johnson, was the winner of the Best Student Presentation. The title of her presentation was “Partially Massless Decoupling Limit of Massive Gravity”.
The award is $200 and gives the recipient the right to advertise her/himself as winning the Division of Gravitational Physics Best Student Presentation at the particular meeting.
Please join in congratulating Laura on this accomplishment!
March 30, 2018
Distinguished University Professor Glenn Starkman memorializes Stephen Hawking
Glenn Starkman, Distinguished University Professor and professor of physics and astronomy, wrote a piece describing the scientific and cultural achievements of the late Stephen Hawking. The article, titled "The reverberating glow of Stephen Hawking's daring theories and elastic mind," was written for cleveland.com.
Starkman depicts the complicated theories that Hawking proposed, noting that, as the physicist had amyotrophic lateral sclerosis, he lost his ability to write and had to perform all of his later calculations in his head. Additionally, Starkman commends Hawking's interest in bringing science to popular culture.
November 27, 2017
Physics’ Week of Defenses!
November 27, 2017
The Art of Calculation
Goldwater Scholar Ben Kuznets-Speck uses mathematical tools to understand complex biological systems.
Read the complete article at: Ben Kuznets-Speck Article
November 10, 2017
Physics’ Reading Day Potluck!
December 15, 2017
12:00 – 1:15 p.m.
2nd floor of Rockefeller Building
One of the year’s favorite events! Try dishes from all over the globe. (View Flyer) 2017 Reading Day Potluck
February 10, 2017
CWRU researchers directly measure how perovskite solar films efficiently convert light to power
Measurement shows potential for building better solar cells by imaging fundamental properties of the material
Solar cells made with films mimicking the structure of the mineral perovskite are the focus of worldwide research. But only now have researchers at Case Western Reserve University directly shown the films bear a key property allowing them to efficiently convert sunlight into electricity.
Identifying that attribute could lead to more efficient solar panels.
Electrons generated when light strikes the film are unrestricted by grain boundaries--the edges of crystalline subunits within the film--and travel long distances without deteriorating, the researchers showed. That means electric charge carriers that become trapped and decay in other materials are instead available to be drawn off as current.
The scientists directly measured the distance traveled--called diffusion length--for the first time by using the technique called "spatially scanned photocurrent imaging microscopy." Diffusion length within a well-oriented perovskite film measured up to 20 micrometers.
The findings, published in the journal Nano Letters, indicate that solar cells could be made thicker without harming their efficiency, said Xuan Gao, associate professor of physics and author of the paper.
"A thicker cell can absorb more light," he said, "potentially yielding a better solar cell."
Efficiency built in
Solar power researchers believe perovskite films hold great promise. In less than five years, films made with the crystalline structure have surpassed 20 percent efficiency in converting sunlight to electricity, a mark that took decades to reach with silicon-based solar cells used today.
In this research, Gao's lab performed spatially scanned photocurrent image measurements on films made in the lab of Case Western Reserve chemistry professor Clemens Burda.
Schematic of scanning photocurrent imaging microscopy of halide perovskite film (side view).
Perovskite minerals found in nature are oxides of certain metals, but Burda's lab made organo-metallic films with the same crystalline structure using methyl ammonium lead tri-iodide (CH3NH3PBI3), a three-dimensional lead halide surrounded by small organic methyl ammonium molecules that hold the lattice structure together.
"The question has been, ‘How are these solar cells so efficient?' If we would know, we could further improve perovskite solar cells," Burda said. "People thought it could be due to unusually long electron transport, and we directly measured it."
Diffusion length is the distance an electron or its opposite, called a hole, travels from generation until it recombines or is extracted as electric current. The distance is the same as transport length when no electric field (which usually increases the distance traveled) is applied.
The labs made repeated measurements by focusing a tiny laser spot on films 8 millimeters square by 300 nanometers thick. The films were made stable by coating the perovskite with a layer of the polymer parylene.
The light generates electrons and holes and the photocurrent, or stream of electrons, is recorded between the electrodes positioned about 120 microns away from each other while the film is scanned along two perpendicular directions. The scanning yields a two-dimensional spatial map of carrier diffusion and transport characteristics.
The measurements showed diffusion length averaged about 10 microns. In some cases, the length reached 20 microns, showing the functional area of the film is at least 20 microns long, the researchers said.
In some materials, grain boundaries decrease conductivity, but imaging showed that these interfaces between grains in the film exerted no influence on electron travel. Gao and Burda say this may be because grains in the film are well aligned, causing no impedance or other detrimental effects on electrons or holes.
Burda and Gao are now seeking federal funds to use the microscopy technique to determine whether different grain sizes, orientations, halide perovskite compositions, film thicknesses and more change the film's properties, to further accelerate research in the field.
This article was originally published Jan. 10.
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