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January 29, 2001

Lian looks to tiny photo cell
to harness sun’s 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 nanomaterials—titanium dioxide particles a million times smaller than a strand of hair—and 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.

“It’s very exciting that we could potentially develop a photo cell to create a better quality of life,” said Lian, who’s 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 industry’s 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 effects—in Lian’s 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 cell.”

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 products—particles measured in namometers, thus the name “nanomaterials”—Lian 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 particle’s 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 energy harvesting.

Lian’s 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 counts—it’s much cheaper, but it still produces less electricity,” Lian said. “Once we’re able to produce the same or more electricity with less cost, then we will have improved the solar cell.”

Chemistry chair Jay Justice said Lian’s 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 he’ll 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.

“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.”


Back to Emory Report Jan. 29, 2001