Squeezing Juice from the Sun: Tapping Solar Energy Could Provide Limitless Power

Focusing on creating autonomous power systems based on flexible thin-film solar cells, Desu is hoping to increase efficiency through novel design and restructuring of the cell itself.

“We’re attacking both sides of the problem: We want an integrated system that can generate power with solar cells and store that power more efficiently and at a lower cost,” said Desu, dean of Binghamton University’s Thomas J. Watson School of Engineering and Applied Science, and the head of the research team tackling how to harness the sun’s energy potential.

Although the typical generation efficiency of these solar cells today is about 10 percent, Desu says that the developing field of nanotechnology can help achieve this goal. When materials are structured into much smaller dimensions as nanoparticles, it increases the number of surfaces. This, in turn, increases the capacity to interact with the environment without increasing the size of the basic unit. Materials also have other unexpected and often beneficial properties when their sizes are reduced to nano levels. Desu’s research will take advantage of these as yet unknown properties in constructing the next generation of thin-film solar cells, in which nanoparticles cover a large surface area to maximize generation efficiency, reduce the cost and increase reliability.

“The solar energy we could access in one day could support the electricity needs of the Earth for a year at the present rate of consumption,” Desu added. “By 2015, solar cells as power sources could be a huge industry.

The other side of the coin in developing lower cost power sources using solar cells is that the energy that is produced must be stored efficiently and still provide ready, reliable access for several years. Desu compares marathon runners and sprinters to explain the current state of energy storage devices.

“Batteries are marathoners — they have high energy density but low power density,” he explained. “Capacitors are the opposite because they can supply high levels of power quickly, such as when you turn on your laptop computer.”

The problem with energy-dense batteries is their size and lifetime, whereas lightning-fast capacitors run down quickly. The solution is to combine the best qualities of both into a supercapacitor, Desu said.

“Potential for solar energy utilization can be maximized when the solar cells are integrated with high-efficient energy storage supercapacitor devices that could accommodate the accelerated power needs. We were able to produce supercapacitors with significantly high energy and power densities with extremely long cycle lifetimes using the advantages of nanostructuring as well as thin-film nanocomposite materials,” he said. “To achieve high-energy density and prevent self-discharge through open circuit reactions, we developed inorganic and organic solid-state electrolytes as gels or membranes with ionic conductors that are biologically derived.”

Integrated solar-cell supercapacitor structures as autonomous power sources are also being investigated, Desu added. And the direct applications of the autonomous power system based on solar cells are found everywhere, not just in computers or electronic gadgets.

“Research should ultimately transfer scientific innovations into useful products and processes that would benefit society. It’s not just curiosity,” he said.

In addition to flexible, large-area autonomous power sources, there is a growing need for highly efficient large-area lighting. For that latter purpose, some members of Desu’s group are developing ZnObased light-emitting diodes (LED). His group has also been developing flexible thin film medical sensing devices. Desu suggests that due to their flexibility and precision detection capacity, these sensing devices could be built into the environment. For example, if built into the walls of a shower stall, the devices would remain unobtrusive yet provide accurate monitoring of potential health threats.

“The future exists in latent form in the present and if we can identify dangerous conditions, such as cancer growth, in their latent phase, intervention is easy and less costly,” says Desu. “We’re trying to migrate flexible electronics into that area of application. In effect, our cars are better monitored than our bodies are.”