Choice of substrate material for epitaxial CdTe solar cells

Epitaxial CdTe with high quality, low defect density, and high carrier concentration should in principle yield high-efficiency photovoltaic devices. However, insufficient effort has been given to explore the choice of substrate for high-efficiency epitaxial CdTe solar cells. In this paper, we use numerical simulations to investigate three crystalline substrates: silicon (Si), InSb, and CdTe itself. Potential problems, especially the non-ideal band alignment of Si and InSb substrates with a CdTe absorber, are found to be a limitation on cell performance. In addition, commercially available CdTe substrates have excessive series resistance leading to a FF loss, and Si has a significant lattice mismatch with CdTe, creating interfacial traps. Possible solutions to overcome the drawbacks of each substrate material are generally discussed.