Successful Solar Cell Doping at EMPA Using Copper
Researchers from the Swiss Federal Laboratories for Materials Science and Technology (EMPA) have been working on the industrialization of flexible, light-weight and low-cost cadmium telluride (CdTe) solar cells on metal foils. Their newly developed cells have increased the energy conversion efficiency from below 8% up to 11.5%.
This type of flexible thin film solar cells require only a minimum amount of material and can be easily manufactured in large quantities. One drawback is that CdTe cells require a transparent supporting material that lets sunlight pass through to reach the light-harvesting layer. CdTe cells in substrate configuration, with inversion of the solar cell’s multi-layer structure, allow the usage of flexible foils made of cost-saving non-transparent material.
However, CdTe cells in substrate configuration on metal foil perform very low efficiencies, below 8% compared to the CdTe cells on glass with 11 to 12% energy conversion efficiency. The low efficiency of CdTe cells in substrate configuration can be increased by adding precise amounts of copper (Cu). This treatment increases the density of positive charge carriers, resulting in a higher photovoltaic power. The amount of Cu has to be precisely controlled. If too little is added, the efficiency does not improve much, and the very same happens if the solar cells are Cu “over-doped”.
“Our results indicate that the substrate configuration technology has a great potential for improving the efficiency even further in the future.” says Stephan Buecheler, a group leader in EMPA’s laboratory for Thin Films and Photovoltaics.
The reference article was published in the journal Nature Communications.