Fabrication of flexible and bifacial Cu(In,Ga)Se2 solar cell with superstrate-type structure using a lift-off process

Flexible and bifacial Cu(In,Ga)Se-2 (CIGS) solar cell with superstrate-type structure utilizing ethylene tetrafluoroethylene (ETFE) was fabricated by a lift-off process. The advantages of the lift-off process performed under low temperature (below 100 degrees C) are to allow to deposit the CIGS layer under high temperature and to use ETFE as superstrate. The superstrate-type structure consists of ETFE/epoxy glue/ZnO:Al (AZO)/ZnO/CdS/CIGS/back contact, where the bilayer of ultra-thin 5-nm-thick Au/400-nm-thick AZO was used as the back contact. The optical and electrical properties of the bilayer of ultra-thin Au/400-nm-thick AZO were examined for the suitable back contact. It is determined that the transmittance of the bilayer of the ultra-thin 5-nm-thick Au/AZO is reasonably suitable in view of optical property. The ohmic-like characteristic at the CIGS/ultra-thin 5-nm-thick Au/AZO interface is attained. Consequently, the flexible and bifacial CIGS solar cell is realized by a lift-off process with conversion efficiency values of 6.2% for the frontside illumination and 0.9% for the backside illumination.