Flexible Cu(In,Ga)Se2 solar cell with superstrate-type configuration fabricated by a lift-off process

Flexible Cu(In,Ga)Se2 (CIGS) solar cells with a superstrate-type configuration including highly transparent ethylene tetrafluoroethylene (ETFE) films as superstrates were fabricated by a lift-off process. The substrate-type CIGS solar cells with a structure of soda-lime glass (SLG)/Mo/CIGS/CdS/ZnO/ZnO:Al were first fabricated. The lift-off process was next utilized to separate the substrate-type CIGS solar cells from their primary SLG/Mo, and the CIGS solar cells were transferred to the alternative ETFE superstrates using transparent epoxy glue. The back electrode (Cu, Pd, or Au) was finally deposited on a side of the CIGS absorber, thereby obtaining the finished flexible CIGS solar cell with a superstrate-type structure (back electrode/CIGS/CdS/ZnO/ZnO:Al/epoxy/ETFE). It is disclosed that there is no crack (or no damage) in the superstrate-type CIGS solar cell after the lift-off process. The contact between CIGS absorber and Au back electrode moreover demonstrates the ohmic characteristic with low resistance. Consequently, the conversion efficiency (η) of the flexible CIGS solar cell with superstrate-type structure using Au as a back electrode is 10.2%, which is almost the same as η (10.7%) of its substrate-type CIGS solar cell with ETFE film on top.