A new thin-film CuGaSe2/Cu(In,Ga)Se2 bifacial, tandem solar cell with both junctions formed simultaneously

Thin films of CuGaSe2 and Cu(In,Ga)Se-2 were evaporated by the 3-stage process onto opposite sides of a single piece of soda-lime glass, coated bifacially with an n(+)-TCO. Junctions were formed simultaneously with each of the p-type absorbers by depositing thin films of n-CdS via chemical bath deposition (CBD) at 60degreesC. The resulting four-terminal device is a non-mechanically stacked, two-junction tandem. The unique growth sequence protects the temperature-sensitive p/n junctions. The initial device (eta = 3.7%, V-oc = 1.1 V [AM1.5]) suffered from low quantum efficiencies. Initial results are also presented from experiments with variations in growth sequence and back reflectors..