Finally Understanding Improved Efficiency in Specific Solar Cells
Sometimes science involves combining two things and getting a result, without knowing why. When this happens the next step is to find out the 'why,' but this can take decades. Researchers at Oak Ridge National Laboratory have recently solved a puzzle from the 1980s concerning cadmium-telluride (CdTe) thin-film solar cells, and how their performance can be increased by adding another material to them.
The thin film CdTe solar cells have been of special interest to many as they could have a lower cost per power output than traditional silicon solar cells. This is partly because of how easy it is to manufacture them. In the 1980s it was discovered that by treating the cells with cadmium-chloride, their efficiency could be raised significantly, and until now it was only known that the chlorine had something to do with it. By analyzing samples with an electron microscope before and after the treatment, the researchers discovered that the chlorine was affecting grain boundaries. Normally grain boundaries reduce efficiency, by inhibiting the movement of charge carriers. With the cadmium-chloride treatment though, some of the tellurium along the grain boundaries is replaced with chlorine atoms. This substitution causes electric fields to form which actually aid the charge carriers' movement.
Now armed with an understanding for why the efficiency increases, it may be possible to create CdTe solar cells with efficiencies much closer to the theoretical maximum of 32%. Combined with their ease of production, they could be a real contender for replacing silicon solar cells.
Source: Oak Ridge National Laboratory