Processing and properties of sub-micron CIGS solar cells

We report on the progress in fabricating CIGS solar cells where the absorber thickness is nominally about 1-mu m. This is done with the objective of reducing the material cost in large-volume production of CIGS where the cost of the high-purity metals, and especially that of In, will become significant factors. At the present time, we have fabricated a 17.1% efficient solar cell for a 1-mu m thick CIGS absorber, and this is arguably the best result for this thickness. Further improvements can be made by optimizing the absorber bandgap and minimizing the window layer losses. We compare the properties of thin films and solar cells fabricated by the three-stage process and co-evaporation. The effect of absorber bandgap and bandgap grading are discussed with the help of experimental data. An analysis of the mechanisms that contribute to the loss of performance in thin cells is provided.