January 29, 2001
Lian looks to tiny photo
to harness suns power
By Michael Alpert
In opposites nearly unfathomable, Tianquan Lian seeks to generate electricity
from particles too small to see with the naked eye, then perhaps some
day smear them over the surface of a car as a means of powering its motor.
An assistant professor in physical chemistry, Lian is studying nanomaterialstitanium
dioxide particles a million times smaller than a strand of hairand
their use in creating electricity from solar energy. He hopes someday
to perfect a far smaller and less expensive solar cell to replace silicon
crystal-based cells currently at the heart of the semiconductor industry.
Its very exciting that we could potentially develop a photo
cell to create a better quality of life, said Lian, whos been
developing the research since coming to Emory in 1996. If we can
improve efficiency substantially, we can use this information to improve
silicone technology also.
And if we can improve the efficiency substantially, he added,
we can replace silicone technology.
Lian, who was born in China and came to the United States in 1988, has
been intrigued with the lesser known use of the semiconductor: creating
electricity from solar energy. With the electronics industrys emphasis
on making devices as small as possible before the leap to final product,
scientists seek to understand how tiny particles behave and then combine
them for various desired effectsin Lians case, harnessing
solar energy to power handheld computers, calculators, watches, etc.
The goal is to come up with a cheaper way to create energy,
said Lian, who has written numerous articles on the behavior of nanomaterials.
The key obstacle to this type of energy is the cost of the solar
Most popularly, solar energy is converted to electricity on the surface
of high-quality silicone crystals, which are often several feet in diameter.
Moreover, silicon, whose production flourished during the height of the
energy crisis of the 1970s, is expensive to make, and the crystals
surfaces must be perfectly constructed to facilitate greatest transfer
of electron energy.
In contrast, Lian uses titanium dioxide particles similar to those in
common products like sunblock, toothpaste and paint pigment. Using particles
thousands of times smaller than those found in such productsparticles
measured in namometers, thus the name nanomaterialsLian
suspends them in liquid to create a white, smooth paste to spread over
conducting glass for viewing under an electron microscope.
Use of minute particles provides exponentially more surface area than
larger silicon crystals because, when suspended in paste, more particle
surfaces are available for electron transfer. For example, cutting a cube
in half creates 12 available sides, instead of six; cutting each of those
in half produces 24, etc.
With the collaboration of organic chemistry Assistant Professor Debbie
Mohler, Lian creates a molecule on the surfaces of each particle and,
with injection of light, energizes an electron along the particles
surface to produce electricity. Exciting the electron to a higher energy
state with light is the initial step, and moving it among particles to
create useable electricity is the ultimate goal.
Lian uses very fast laser techniques to study the dynamics of the nanomaterials.
With pulsations of light too brief for the naked eye to perceive, Lian
studies the excitement and movement of electrons on the particles
surfaces and the electricity produced.
He is especially interested in connecting nanoparticles to create electrodes
with large effective surface area and fast electron transfer rate to heighten
Lians nanomaterial research, first conceived in Europe in the early 1990s, is one of several technologies being developed to rival the cost and efficiency of current solar cell technology.
Titanium oxide is much cheaper to make; even better, it produces nearly
none of the environmentally unfriendly waste of silicone production.
But, Lian pointed out, though nanomaterials are cheaper, they are not
yet as efficient as silicone.
When you look at the cost per watt[which is] what really
countsits much cheaper, but it still produces less electricity,
Lian said. Once were able to produce the same or more electricity
with less cost, then we will have improved the solar cell.
Chemistry chair Jay Justice said Lians work may have practicality
beyond what some first think. I think his research could have a
lot of utility for society, Justice said. I think hell
definitely be very successful.
Mohler, who has helped Lian discover which compounds have the best electron
transfer characteristics, believes cheaper sources of energy can benefit
All you have to do is think of the price of natural gas, and you can see there needs to be an alternative, she said. The sun is the main source of energy for the entire planet, so it only makes sense that we make the best use of it.