College of Engineering News • Iowa State University

Accessible, Affordable Solar

Assistant Professor Sumit Chaudhary joined Iowa State with a vision of turning his interest in nanotechnology and solar cells into a program that would make the conversion to solar energy inexpensive and widespread.

His vision is quickly becoming a reality, as Chaudhary works toward enhancing the efficiency and convenience of flexible, organic-based plastic solar cells. His efforts could dramatically increase the accessibility of solar energy, providing a stable source for areas without dependable energy while also reducing the need to “plug in” that has become an essential part of our increasingly mobile lifestyle.

Narrowing down a broad field of interest

Chaudhary’s doctoral research at the University of California, Riverside, focused on nanoscale optoelectronic materials and devices. He was drawn to the area, he says, because it offered hands-on experience that was highly interdisciplinary and had a significant potential impact.

When Chaudhary entered the field, new materials such as carbon nanotubes, fluorescent nanocrystals, and conducting plastics were emerging. These new resources offered him the chance to experiment, combining materials for functionalities never before imagined. Over the course of his research, Chaudhary’s work with both these materials and biomolecules was unique, as he invented new designs for efficient light-emitting diodes, solar cells, and optical DNA probes.

After much success in the general field of optoelectronics, Chaudhary’s research interests eventually narrowed to solar cells, the one area within the field that he feels can completely change the world. However, in the form of the large, bulky silicon panels in use today, solar cells are costly to produce and install.

“To make solar energy truly accessible for everyone, we need to move away from today’s solar panel model,” Chaudhary says. “Our direction should be to create pliable, versatile solar cells that lend themselves to inexpensive manufacturing and universal use, leading us finally to the solar paint or solar fabric paradigm.”

Making the move to such a model requires dedication to extensive research and experimentation, an endeavor Chaudhary was fully aware of and eager to begin. “There was a great opportunity for me to start a program at Iowa State,” he says. “When I came here, I knew I would be able to make a significant contribution to nanotechnology-enabled solar energy research.”

Moving from bulky silicon to pliable plastic

Since joining Iowa State in fall 2007, Chaudhary has set up the Nano Architectonics and Nano Organo-electronics (NANO) lab to pursue his interests. In the lab, solar cells are developed in an inert atmosphere glove box, an area Chaudhary refers to as the soul of his lab.

“The boxes make our research possible,” Chaudhary says. “They have all the fabrication tools integrated within and are completely sealed off from oxygen and moisture to prevent any degradation during fabrication.”

Chaudhary and his students work with conjugated polymers, materials that combine the electrical properties of traditional semiconductors with the flexibility of plastics to develop novel architectures for highly efficient solar cells. The fabrication process, he notes, is compatible with a roll-to-roll manufacturing process, making the cells amenable to printing in much the way that newspapers are rolled off a printing press.

Prior to coming to Iowa State, Chaudhary had already seen some success in this area, developing solar cells with five percent power conversion efficiency—equal to the world record for an organic technology. Yet while five percent efficiency is impressive, he says, the cells should be both stable and at least ten percent efficient before going on the market.

The cells’ efficiency rate is just one challenge Chaudhary’s group in the NANO lab is addressing. In addition, the group also seeks to develop a product that can overcome some of the classic tradeoffs in solar technology, especially with regard to the polymer films that make up the cells.

“Solar cells need thick polymer films to absorb maximum light,” Chaudhary observes, “but require thinner films to deliver all the produced charges as current.”

There are several approaches Chaudhary is investigating to address this challenge. One involves developing three-dimensional hybrid organic-inorganic structures that can effectively decouple the optical and electronic functions, similar to the mechanism plants employ during photosynthesis.

“When we fabricate solar cells, we test a variety of compositions through which we find our way to the devices with highest efficiency,” Chaudhary says.

Building momentum for the future

While Chaudhary and his research team have made significant leaps toward a marketable alternative to conventional solar arrays, he is nonetheless cautious not to overreach when discussing commercial time frames.

“We are proud of what we have accomplished up to this point,” Chaudhary says. “But we know it will take us at least five years before we have something that can reach our households.”

Although Chaudhary’s primary department in the college is electrical and computer engineering, he also holds a courtesy appointment with materials science and engineering, an affiliation he says is crucial to the future of solar energy. According to Chaudhary, this interdisciplinary approach will help further his research applications.

“There are countless approaches and directions we can take for harnessing solar energy efficiently,” Chaudhary notes. “Bringing those ideas together in one lab gives us more ways to assess the problem and come up with the best solution.

“Besides,” he continues, “nurturing a cross-disciplinary bent of mind, we keep our eyes open to developments in other fields of science and engineering, trying to foster unique collaborations. This is the key for accelerated discovery in the emerging area of organic-based electronics.”

The solar cells Chaudhary is developing for charging portable devices are just the beginning. With time and continued research, he predicts, solar cells will be woven into our fabrics and built into the paint, roofing, windows, and curtains of our homes. A remarkable shift from the massive panels that harness solar energy today, we will not even notice the solar cells of tomorrow.

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