It’s not quite the same as a nice cucumber or grilled cheese sandwich, but researchers at Princeton researchers have found that a unique sandwich of materials significantly boosted the performance of photovoltaic devices by essentially trapping more light. The resulting device is only nanometers thick and could herald much cheaper solar cells.

Unlike silicon photovoltaics, organic PV uses more flexible materials and thinner materials allowing the resulting devices to take on different forms and be produced with less energy. Many can be deposited at room temperatures in normal conditions as opposed to under high heat and or vacuums. Such advances mean they’re cheaper to produce. However, they’re also much less efficient—currently. So even if an organic cell is 100 percent more efficient than a 4 percent efficient cell, it would only be about 8 percent efficient, while silicon cell is closer to 20 percent efficient. 

The technology being developed at Princeton might change that. It uses a nanostructured "sandwich" of metal and plastic that collects and traps light, according to Joseph C. Elgin Professor of Engineering Stephen Chou, who is leading the research. The system he and his team developed is called a "plasmonic cavity with subwavelength hole array" or PlaCSH.

The array includes a fine metal gold mesh 30 nanometers thick with holes just 175 nanometers wide and 25 nanometers apart. The mesh covers a thin strip of semiconducting material which is sandwiched against the backsheet. And interesting thing about the mesh is that it should be able to work with any semiconductor, be it silicon, plastic or gallium arsenide, however it was tested with 85-nanometer-thick plastic. 

The mesh essentially traps light as it strikes the device because all the parts of the device are smaller than the wavelength of the light being collected, according to Princeton. The device Chou's team created only reflected about 4 percent of light and absorbed as much as 96 percent. “It is like a black hole for light," Chou said. "It traps it," he said.

“It demonstrates 52 percent higher efficiency in converting light to electrical energy than a conventional solar cell,” Princeton said. In all, the device represented an increase the efficiency of the solar cells by 175 percent.

The researchers expected an increase in efficiency from the technique, "but clearly the increase we found was beyond our expectations," Chou said.

Chou and electrical engineering graduate student Wei Ding published their research in the journal Optics Express. The research was supported by the Defense Advanced Research Projects Agency, the Office of Naval Research and the National Science Foundation. The team will continue to experiment and refine the material.