In-situ annealing of Cu(In,Ga)Se2 films grown by elemental co-evaporation

The effect of in-situ post-deposition annealing on Cu(InGa)Se2 films grown by elemental co-evaporation on microstructure and solar cell performance has been characterized. Films were deposited at a substrate temperature of 400°C and then annealed in-situ at 400°C, 475°C, 500°C and 550°C for times from 1 – 60 min. Devices made from films grown at 400°C and then annealed at 550°C for 1 minute had comparable efficiency to devices made from films grown at 550°C. Little or no grain growth was observed in SEM cross-section imagery for films annealed at 400°C, 475° or at 550°C for 1 minute but substantial grain growth was seen in films annealed at 550°C when the anneal time was increased to 10 minutes or more. Device performance also improved as a result of post-deposition annealing, but the improvement in VOC took place even when grain growth appeared stagnant. A decrease in the XRD (112) FWHM for such films, however, indicated that both post-deposition annealing and Cu-rich growth caused a change in the films. VOC was correlated with this measure of Cu(InGa)Se2 film evolution for 0.55 V ≪ VOC ≪ 0.65 V.