Lift-Off Process for Flexible Cu(In,Ga)Se2 Solar Cells

Abstract

A lift-off process for flexible Cu(In,Ga)Se2 (CIGS) solar cells was developed. After the growth of a CIGS thin film on a Mo/glass substrate at 550 °C, the CIGS film was transferred to polyimide and poly(tetrafluoroethylene) films. Process temperatures for the device fabrication after the transfer were less than 100 °C. The conversion efficiencies of the lift-off CIGS solar cells were similar and were almost one-half that of a CIGS solar cell prepared by a standard process. The difference was mainly due to the low fill factor caused by a poor back-contact property and the low short-circuit current caused by an inappropriate band gap profile in the CIGS layer. There still remain problems related to the improvement in efficiency; however, this is the first report on flexible CIGS solar cells on a low-thermal-tolerance substrate. We demonstrated the possibility of freedom of substrate material choice in CIGS solar cells.