New cell design promises more efficient conversion of solar energy

Generating electricity from sunlight offers a clean, safe, renewable option for producing power. The problem with expanding its use has always been the high cost.

One major key to solving the problem is coming up with photovoltaic cell technology that is more efficient at converting solar light into electrical energy. The fewer cells it takes to generate substantial amounts of energy, the less expensive it will be to harness solar power for providing electricity.

A promising new approach to achieving the goal is being developed by Arizona State University engineers Cun-Zheng Ning and Derek Caselli. Ning is a professor in the School of Electrical, Computing and Energy Engineering, one of the ASU’s Ira A. Fulton Schools of Engineering. Caselli is pursuing a Ph.D. in electrical engineering.

They’ve designed photovoltaic cell architecture that uses particular materials in specific arrangements to enable cells to more efficiently capture sunlight for conversion into electricity.

Details of the project, which is supported by the U.S. Army Research Office, are presented in a recent article  by Ning and Caselli posted on the website of the International Society for Optics and Electronics – called SPIE – that works to advance light-based technologies.

They describe a design that places different solar-cell materials side by side beneath other materials that act as a “dispersive concentrator.”

This arrangement enables sunlight to be separated into different colors before it is absorbed by the material within the cells. The absorption cells are arranged in a way that ensures each color is matched to the material best able to absorb it.

Caselli explains: “Sunlight can be separated into different components of the light spectrum and distributed among the materials within the cells, so that each photon is absorbed by the one best suited to convert it to electricity."

The key innovation is making the absorbing materials in all the cells in a one-step fabrication process on a single substrate – or platform.  This would eventually provide high-efficiency, low-cost solar power, Ning says.

Ning and Caselli also are developing technology for a new fabrication process for the new type of solar cell.  It could be less expensive than many current cell-fabrication processes, they say, and produce new cells that will be as efficient at converting sunlight into electrical energy as the highest-performing cells now on the market.

“Our simulation results show efficiencies roughly similar to those obtained by the highest-performing cells, but there are a number of ideal conditions that we assume in our simulations for the sake of simplicity,” Caselli says.

"We suggest there are a number of ways the cell design could be optimized to make them as efficient as the highest-performing cells at a lower cost,” he says.
 
He says the geometry of the cells could be altered to maximize their light-absorption capability, and different semiconductor materials could be used that would enhance cells’ ability to conduct electricity.