Pei Dong, a graduate student at Rice University, holds a lab-built solar cell that combines a carbon nanotube current collector and a sulfide-based electrolyte. The combination could make such solar cells more efficient and less expensive than current dye-sensitized units. Photo by Jeff Fitlow |
The
single-wall nanotube arrays, grown in a process invented at Rice, are
both much more electroactive and potentially cheaper than platinum, a
common catalyst in dye-sensitized solar cells (DSCs), said Jun Lou, a
materials scientist at Rice. In combination with newly developed sulfide
electrolytes synthesized at Tsinghua, they could lead to more efficient
and robust solar cells at a fraction of the current cost for
traditional silicon-based solar cells.
Lou
and co-lead investigator Hong Lin, a professor of materials science and
engineering at Tsinghua, detailed their work in the online, open-access
Nature journal Scientific Reports this week.
DSCs
are easier to manufacture than silicon-based solid-state photovoltaic
cells but not as efficient, said Lou, a professor of mechanical
engineering and materials science. “DSCs are sensitized with dyes,
ideally organic dyes like the juices from berries – which some students
have actually used in demonstrations.”
Dyes
absorb photons from sunlight and generate a charge in the form of
electrons, which are captured first by a semiconducting titanium oxide
layer deposited on a current collector before flowing back to the
counter electrode through another current collector. Progress has been
made in the manufacture of DSCs that incorporate an iodine-based
electrolyte, but iodine tends to corrode metallic current collectors,
which “poses a challenge for its long-term reliability,” Lou said.
Iodine
electrolyte also has the unfortunate tendency to absorb light in the
visible wavelengths, “which means fewer photons could be utilized,” Lou
said.
So
Tsinghua researchers decided to try a noncorrosive, sulfide-based
electrolyte that absorbs little visible light and works well with the
single-walled carbon nanotube carpets created in the Rice lab of Robert
Hauge, a co-author of the paper and a distinguished faculty fellow in
chemistry at Rice’s Richard E. Smalley Institute for Nanoscale Science
and Technology.
“These
are very versatile materials,” Lou said. “Single-walled carbon
nanotubes have been around at Rice for a very long time, and people have
found many different ways to use them. This is another way that turns
out to be very well-matched to a sulfide-based electrolyte in DSC
technology.”
Both
Rice and Tsinghua built working solar cells, with similar results. They
were able to achieve a power conversion efficiency of 5.25% – lower
than the DSC record of 11% with iodine electrolytes and a platinum
electrode, but significantly higher than a control that combined the new
electrolyte with a traditional platinum counter electrode. Resistance
between the new electrolyte and counter electrode is “the lowest we’ve
ever seen,” Lou said.
There’s
much work to be done, however. “The carbon nanotube-to-current
collector still has a pretty large contact resistance, and the effects
of structural defects in carbon nanotubes on their corresponding
performance are not fully understood, but we believe once we optimize
everything, we’re going to get decent efficiency and make the whole
thing very affordable,” Lou said. “The real attraction is that it will
be a very low-cost alternative to silicon-based solar cells.”
Pei
Dong, a graduate student in Lou’s lab, and Feng Hao, a graduate student
at Tsinghua, are lead authors of the paper. Co-authors include Rice
graduate students Jing Zhang and Philip Loya, Yongchang Zhang of
Tsinghua and Professor Jianbao Li of Hainan University, China.
The
project was supported by the National High Technology Research and
Development Program of China, the Welch Foundation and the Faculty
Initiative Fund at Rice.
Source: Rice University
