Sodium co-evaporation for low temperature Cu(In,Ga)Se2 deposition

Abstract Cu(In,Ga)Se2 (CIGS) thin-films were deposited ‘in-line’, i.e. the substrate is moved with respect to the sources on soda-lime glass (SLG). To better understand the role of substrate temperature during CIGS deposition, we successively decreased the substrate temperature. The CIGS layers were analysed using sheet resistance measurements, SEM and XRD; in addition, solar cell devices were prepared. We found significant deterioration in solar cell parameters and a different morphology with decreasing substrate temperature. The results were compared with the results from CIGS layers and devices grown on sodium free glass. In a second step, a sodium evaporation source was added to the deposition system to provide additional sodium during film growth. With this technique, solar cells (0.5 cm2) with efficiencies of 11.7% (SLG) and 10.9% (Na-free glass) were fabricated ‘in-line’ at a substrate temperature of 400°C.