ORNL Optimizes Formula for Cadmium-Tellurium Solar Cells

Solar cells based on cadmium and tellurium could move closer to theoretical levels of efficiency as a result of research at the Department of Energy’s Oak Ridge National Laboratory.
 
A team led by Jonathan Poplawsky of the Center for Nanophase Materials Sciences used advanced microscopy techniques to discover efficiency differences of crystalline structures of various mixtures of cadmium, tellurium and selenium. In fact, selenium is an integral part of the formulation that resulted in a world record for solar cell efficiency. The team’s paper is published in Nature Communications.
 
While some of today’s solar cells use a blend of cadmium and tellurium to convert light into electricity, adding the optimum amount of selenium in the right places could help increase efficiency from the current mark of about 22 percent to levels approaching the theoretical limit of 30-33 percent. The trick is to determine the best ratio of selenium.
 
“Using different microscopy methods, we were able to gain a better understanding of the phases, compositions and crystalline structures that allow these materials to convert light into electricity more efficiently,” said Poplawsky, adding that the availability of data is limited. “In some instances, adding too much selenium changes the crystalline structure of cadmium-tellurium and dramatically reduces the conversion efficiency.”
 
For this study, researchers studied four solar cells with different selenium contents – and corresponding changes in crystal structure – and learned that the one with the highest level of selenium did not perform well. Neither did the one with the lowest selenium content. The alloy composition that performed best consisted of approximately 50% cadmium, 25% tellurium and 25% selenium.
 
Poplawsky noted that solar panels typically use silicon as the material for converting sunlight into electricity. Cadmium-telluride, however, has an advantage over silicon because it can absorb the same amount of sunlight with 98% less semiconducting material, thus reducing the overall cost of the solar panel.
 
ORNL co-authors of the paper, titled “Structure and Compositional Dependence on the CdTexSe1-x  Alloy Layer Photoactivity in CdTe-based Solar Cells,” are Wei Guo, Karren More and Donovan Leonard.
 
This research was funded by DOE’s SunShot Initiative in collaboration with the National Sciences Foundation.