Solar cells that can be printed

The development of a new solar cell may provide consumers a way to harness solar rays as a form of renewable energy, inexpensively.

Researchers at the New Jersey Institute of Technology (NJIT) have developed an inexpensive solar cell that can be painted or printed on flexible plastic sheets.

The new solar cells use a carbon nanotubes complex, which is a molecular configuration of carbon in a cylindrical shape. These nanotubes are about 50,000 times smaller than a human hair.
"The process is simple," said lead researcher and author Dr. Somenath Mitra, professor and acting chair of NJIT's department of chemistry and environmental sciences.

He foresees the day when consumers will even be able to print sheets of these solar cells with inexpensive home-based inkjet printers.

"Consumers can then slap the finished product on a wall, roof or billboard to create their own power stations," Mitra said.

How they work

While the new solar cells are very thin, just one nanotube can conduct current better than any conventional electrical wire, Mitra said.

"Actually, nanotubes are significantly better conductors than copper," he added. Mitra and his research team took the carbon nanotubes and combined them with tiny carbon "buckyballs" (carbon molecules in a hollow sphere configuration), to form snake-like structures, also called polymers.

Buckyballs are able to trap electrons, although they can't make electrons flow.

When the polymers are exposed to sunlight, and the buckyballs will grab the electrons.

The nanotubes, on the other hand, behave like copper wires, and so are able to make the electrons flow, Mitra explained.

"Using this unique combination in an organic solar cell recipe can enhance the efficiency of future painted-on solar cells," Mitra said.

"Someday, I hope to see this process become an inexpensive energy alternative for households around the world."

Renewable energy challenges

Harvesting energy directly from abundant solar radiation using solar cells is becoming increasingly for future global energy strategy, Mitra said.

But when it comes to harnessing renewable energy, challenges remain.

Expensive, large-scale infrastructure such as windmills (for wind power) or dams (for hydroelectric power) are necessary to drive renewable energy sources.

Even when solar power is being considered, there is the challenge of obtaining enough materials. Purified silicon, already in high demand for making computer chips, is a core material for fabricating conventional solar cells.

Moreover, the processing of purified silicon is beyond the capabilities of most consumers, Mitra notes.

"Developing organic solar cells from polymers, however, is a cheap and potentially simpler alternative," he said.

When contacted by In.Tech, Mitra claimed the process is commercially viable.

"We foresee a great deal of interest in our work because solar cells can be inexpensively printed or simply painted on exterior building walls and rooftops.

"Imagine some day driving in your hybrid car with a solar panel painted on the roof, which is producing electricity to drive the engine," Mitra said.

However, he concedes that the NJIT cells need improvement in the area of energy conversion efficiency, a measure of the power converted from absorbed light.

The NJIT cells currently run at only around 1% efficiency, compared to more than 25% efficiency for the best conventional solar cells.

"We should be able to improve (the cell efficiency) as we do more research, but the advantage is in the low capital investment required for this technology, which is significantly lower than for conventional solar cells."

Current silicon-based solar cells in use are relatively complex; they share many of the same processing and manufacturing techniques used for other semiconductor devices such as processors and memory chips.

Mitra's work was first published in the June edition of the Journal of Materials Chemistry.

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