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

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 200°C 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 180°C annealing, where the series resistance of CdTe cells was a minimum of 0.5 Ω·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.