The effects of sodium on the growth of Cu(In,Ga)Se2 thin films using low-temperature three-stage process on polyimide substrate

In this work, Cu(In,Ga)Se-2 (CIGS) absorbers were deposited on polyimide substrates using the low-temperature three-stage process, and different sodium incorporation methods were applied to investigate the effects of Na on the CIGS growth. It was found that Na affected the CIGS film growth significantly during the second stage of the process, and resulted in a higher Ga content near the back contact. The CIGS thin films with different Na-incorporation methods exhibited similar electrical parameters. A modelling investigation was also implemented by using the wxAMPS software package to quantitatively analyse the effects of different Ga gradient to the device characteristics. Finally, the device performance showed little difference between the post-deposition treatment of NaF and the co-evaporation of NaF during the third stage.