Back contact formation using Cu2Te as a Cu-doping source and as an electrode in CdTe solar cells

Abstract

Cu2Te was utilized as a Cu source for p+ doping in CdTe and as a primary back contact material in CdTe solar cells. A 60 nm-thick Cu2Te layer was deposited on CdTe film by evaporating Cu2Te and the samples were annealed at various temperatures. An amorphous layer was found at the Cu2Te/CdTe interface, while the Cu2Te has both orthorhombic and hexagonal phases. Annealing at 2001C completely crystallized the amorphous interlayer and enhanced the transformation of orthorhombic phase into hexagonal phase that has a coherent interface with CdTe. A good p+ contact was formed at 1801C annealing, where the series resistance of CdTe cells was a minimum of 0.5O ohm· cm2 and the fill factor and open-circuit voltage were significantly improved. With the good p+ contact, it is possible to determine the exact dopant profile at the CdS/CdTe junction.