The ‘Misjudge Material’ can be the next Solar Cell Technology

Researchers are step close to a solar energy innovation which claims to vie traditional energy sources in electricity generation. Currently, silicon solar cells available in the solar cell market making manufacturing costs a bit tight for the manufacturers.

But, a team Led by the U.S. Department of Energy’s National Renewable Energy Laboratory and Washington State University and the University of Tennessee is known to have the capability to enhance the maximum voltage available from a cadmium telluride (CdTe) solar cell, overcoming the traditional generation capabilities and improving efficiency. CdTe solar cells offer a low-cost alternative. They have the lowest carbon footprint of any other solar technology and perform better than silicon in real world conditions, including in hot, humid weather and under low light. However, until recently, CdTe cells haven’t been as efficient as silicon-based cells.

Making debatable of the six decades old thought on CdTe materials limitation to 900 millivolts, one key area where CdTe has underperformed was in the maximum voltage available from the solar cell, called open-circuit voltage. The research team improved cell voltage by shifting away from a standard processing step using cadmium chloride. Instead, they placed a small number of phosphorus atoms on tellurium lattice sites and then carefully formed ideal interfaces between materials with different atomic spacing to complete the solar cell. This approach improved the CdTe conductivity and carrier lifetime each by orders of magnitude, thereby enabling the fabrication of CdTe solar cells with an open-circuit voltage breaking the 1-volt barrier for the first time.

The innovation establishes new research paths for solar cells to become more efficient and provide electricity at lower cost than fossil fuels.

“It’s a significant milestone. It’s been below 900 millivolts for decades,” said Kelvin Lynn, Regents professor in WSU’s School of Mechanical and Materials Engineering and Department of Physics, who led WSU’s effort.

The NREL researchers treated the crystals, built and characterized the solar cells, while WSU researchers, including Santosh Swain and Tursun Ablekim, developed -the crystal material used in the cells. The WSU researchers grow their crystals in a technique called melt growth, which allows precise control over purity and composition. Purity is extremely critical to the process, so the researchers mix, prepare and vacuum-seal the materials in an industry-standard clean room. They then synthesize the crystal in a furnace above 1100 degree °C and then cool it from the bottom up at a rate of about one millimeter per hour. The researchers then cut the crystal into polished wafers to make the solar cells.

“Others have tried dopants, but they didn’t have the control and purity that we have. And, the purity matters,” said Lynn. “WSU is known for growing really high quality and purity crystals. You have to control every step.”

While researchers have improved silicon-based cells almost to their theoretical limit, there is significant room for efficiency improvements for cadmium telluride, which could be bettered by an additional 30 percent, said Lynn.