The status of and challenges in CdTe thin-film solar-cell technology

Polycrystalline CdTe thin-film solar cells have shown high potential for low cost, large-area module fabrication. But successful large-scale commercial production has been elusive. Fabrication of the basic n-CdS / p-CdTe heterojunction is possible by a wide variety of methods, including close-spaced sublimation, vapor-transport deposition, electrodeposition, chemical bath deposition, and magnetron sputtering. An overview of these methods is presented as well as the role of the postdeposition "activation" treatment using CdCl2 and issues related to the difficulty of obtaining low resistance back contacts to CdTe. We present some of our recent fabrication results using rf magnetron sputtering and discuss some of the advantages that appear possible from the use of sputtering methods in this class of materials. Some of these advantages are particularly relevant as the polycrystalline thin-film PV community addresses the challenges of fabricating tandem cells with efficiencies over 25%.