SOLAR CELLS AND
he space industry now favors gallium alloys over silicon
for use in the solar cells that power satellites because a
smaller, lighter system can save money when launched
into space. However, gallium nitride hasn’t been one
of those preferred alloys. Materials engineers at Cornell have
instead investigated other ways to make solar cells more
efficient, using help from one of Cornell’s most powerful
research tools: the Cornell High Energy Synchrotron Source,
also known as CHESS.
In 2008, a group of researchers engineered a solar cell as
a nano-manufactured polymer film just 400 nanometers thick.
The rate at which it could convert sunlight to electricity was
low compared to silicon-based photocells, but it demonstrated a
novel method for developing low-cost, thin solar cells.
Leading that research group was Uli Wiesner, the Spencer
T. Olin Professor of Materials Science and Engineering, who
published a related study in 2015 demonstrating how to
optimize the fabrication conditions of a thin-film solar cell.
Wiesner focused on using metal halide perovskites, which
have recently garnered attention from the materials community
for their unique crystal structure, giving them properties prime
for solar applications. But in order for them to be as defect-free as possible, Wiesner used the Cornell synchrotron to
characterize how different lead-salt solutions helped optimize
the perovskite films.
Buried 40 feet below Cornell’s surface, the high-energy
x-ray facility spans a half-mile circumference that loops under
the south campus athletics fields. And while CHESS is one
of many facilities used by Cornell’s materials scientists and
engineers, it’s the only one that can send electrons traveling at
99.9999995 percent the speed of light in order to emit powerful
x-rays that can be directed toward materials.
Teams of researchers use the synchrotron facility around
the clock to characterize new materials, and like Wiesner, they’re
trying to get a closer look at crystal structures in order to better
understand how they relate to the material properties they hope
“We have researchers studying materials and systems
across any spectrum you choose to define—from soft matter, like
protein molecules floating in solution, all the way to super-hard,
super-strong materials used to build airplane engines,” said
Ernie Fontes, associate director of CHESS.
CHESS is one of only five facilities in the country that
conducts synchrotron x-ray research, so securing time inside
remains coveted. Fontes says the facility’s database has nearly
500 active projects, and out of the more than 1,000 researchers
Atomic force microscopy images of perovskite films engineered using
substrates derives from three different lead sources (a,b,c) and a
vapour-deposited film base (d). The circled dark spots show gaps in
samples a and b, while sample c shows no flaws.
The underground footprint of the High Energy Synchrotron Source is highlighted in white, showing the facility’s half-mile circumference buried
40 feet below Cornell’s south campus.