Nanostructures with different photoconduction properties  (Source: University of Pennsylvania)
The process can also be customized for different applications

Researchers have found a new technique of collecting energy from light for improved solar energy harvesting, which could lead to better optoelectronic devices.

Researchers from the University of Pennsylvania -- led by Dawn Bonnell, Penn's vice provost for research and Trustee Professor of Materials Science and Engineering in the School of Engineering and Applied Science -- have used plasmonic structures and a technique called ferroelectric nanolithography to make a process more efficient than conventional photoconduction. 

The study is based on Bonnell and colleagues' previous work from 2010. At that timethey reported the fabrication of a plasmonic nanostructure that induced and projected an electrical current across molecules. Plasmons are a collective oscillation of electrons. Ferroelectric nanolithography was used to design the material, which is an array of gold nanoparticles that tends to get plasmons excited due to optical radiation.

However, the team couldn't exactly prove that the improved transduction of optical radiation to an electrical current was due to excited plasmons creating hot electrons. 

"We hypothesized that, when plasmons are excited to a high energy state, we should be able to harvest the electrons out of the material," said Bonnell. "If we could do that, we could use them for molecular electronics device applications, such as circuit components or solar energy extraction."

Now, in the latest study, Bonnell and the team varied the the size of the gold nanoparticles, the size of the porphyin molecules and the spacing of those components. They also designed certain structures that ruled out other possibilities so that the enhanced photocurrent could only  be from the hot electrons harvested from the plasmons.

The materials fabricated from gold particles and light-sensitive molecules of porphyin (which consisted of precise sizes and were arranged in specific patterns) made the plasmons excited by optical radiation and caused them to induce an electrical current that can move in a pattern determined by the size and arrangement of the gold particles, as well as the electrical properties of the environment. These materials can enhance the scattering of light and can increase absorption in solar cells. 

By changing the size and spacing of nanoparticles, the wavelength of light to which the plasmon responds is adjusted. This means the process can be customized.

The results found increases of three to 10 times in the efficiency through the use of plasmons and ferroelectric nanolithography compared to conventional photoexcitation.

Source: Science Daily

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