South Dakota State Researches Organic Photovoltaics

Organic photovoltaics, or OPVs, are less expensive to produce than traditional devices for harvesting solar energy, and Qiquan Qiao, assistant professor in South Dakota State University's electrical engineering and computer science department, is trying to discover the best materials to use to make them.

The new technology is sometimes referred to as "molecular electronics" or "organic electronics" — organic because it relies on carbon-based polymers and molecules as semiconductors rather than inorganic semiconductors such as silicon.

"These devices can be fabricated by inexpensive, solution-based processing techniques similar to painting or printing," Qiao said. "The ease of production brings costs down, while the mechanical flexibility of the materials opens up a wide range of applications."

Organic photovoltaics are made up of thin films of semiconducting organic compounds that can absorb photons of solar energy. Typically an organic polymer, or a long, flexible chain of carbon-based material, is used as a substrate on which semiconducting materials are applied as a solution using a technique similar to inkjet printing.

"The research at SDSU is focused on new materials with variable band gaps," Qiao said. "The band gap determines how much solar energy the photovoltaic device can absorb and convert into electricity."

Qiao explained that visible sunlight contains only about 50 percent of the total solar energy. That means the sun is giving off just as much non-visible energy as visible energy.

"We're working on synthesizing novel polymers with variable band gaps, including high, medium, and low-band gap varieties, to absorb the full spectrum of sunlight. By this we can double the light harvesting or absorption," Qiao said.

The university's scientists plan to use the variable band gap polymers to build multi-junction polymer solar cells or photovoltaics. These devices use multiple layers of polymer/fullerene films that are tuned to absorb different spectral regions of solar energy. Ideally, photons that are not absorbed by the first film layer pass through to be absorbed by the following layers. The devices can harvest photons from ultraviolet to visible to infrared in order to efficiently convert the full spectrum of solar energy to electricity.

This work is funded in part by the university's electrical engineering doctorate program and by National Science Foundation and South Dakota EPSCoR, the Experimental Program to Stimulate Competitive Research.

comments powered by Disqus