Breakthrough in solar energy

From staff reports

WSU researchers have made breakthrough improvements on photovoltaic technology used to generate solar energy.

In cooperation with the National Renewable Energy Laboratory (NREL) and the University of Tennessee, WSU researchers have reached the one-volt milestone for open-circuit voltage of cadmium telluride (CdTe) photovoltaics.

For about 30 years, researchers have been working with CdTe but have only been able to reach 800 to 900 millivolts, about 80 percent of a volt, said Kelvin G. Lynn, regents professor in the school of mechanical and materials engineering.

According an article from the scientific journal Nature Energy, open-current voltage is important because it determines the amount of cells needed to reach an optimal power level.

Making CdTe more efficient means solar cells take less space and create more power, Lynn said.

Silicon photovoltaics are currently the most widely used type of solar cell because of their low cost and relatively high output. These new developments in CdTe photovoltaics will drive down the cost, making it more competitive with silicon, said researcher Santosh Swain.

Companies would prefer to use CdTe because it works better in warmer conditions as opposed to silicon and copper photovoltaics.

Copper has a tendency to move around when it gets hot,” Lynn said. “Silicon always gets worse, but CdTe seems to keep going on and on and on.”

It is also better for the environment.

“It doesn’t use very much raw material,” Lynn said. “It is the thinnest solar cell.”

WSU’s role in the research was to grow raw CdTe crystals, send samples to NREL for testing and send crystals to University of Tennessee where researchers use them to see how they interact with the other materials in a solar cell, Swain said.

CdTe photovoltaics were previously treated with cadmium chloride (CdCl2) or copper. The WSU research team treated the CdTe with foreign phosphorous atoms to change the growth of the crystal, Swain said.

According to the journal article, the phosphorous concentration gave the cell properties comparable to those reported in gallium arsenide, currently the best performing material for single-junction solar cells.

New CdTe can be competitive with silicon, Swain said.

“We need to figure out how to replicate these properties when they are on a film,” Swain said. “Our developments are still crystalline.”

Along with Lynn and Swain, Tursun Ablekimw is a leading researcher on CdTe photovoltaics.

Reporting by Forrest Holt