Modified co-evaporation process for fabrication of 4 cm x 4 cm large area flexible CIGS thin film solar cells on polyimide substrate

A modified three-stage co-evaporation process has been studied in our work for the fabrication of large area Cu(In, Ga)Se-2 (CIGS) thin-film solar cells on flexible polyimide substrates. According to our results, the open circuit voltage and fill factor are improved significantly by using the modified process. In order to quantitatively analyze the effects of the modified band-gap gradient in CIGS thin film, a modeling investigation is carried out by employing a simulation program, wxAMPS. The simulation indicates that the device improvement is not only attributed to the refined Ga gradient profile, but also to the better crystalline quality. The elemental evaporation rates and the content of Cu are found to be key factors for the large-area solar cell preparation. Finally, 16 cm(2) CIGS thin-film solar cells on PI substrates are fabricated, and the highest cell efficiency has achieved 7%.