Modification of the three-stage evaporation process for CuIn1−xGaxSe2 absorber deposition

CuIn1−xGaxSe2 absorbers for highest efficiency state-of-the-art solar cells are generally deposited by a sequential three-stage coevaporation process from elemental sources. We investigated the influence of the maximum copper concentration used during processing in the second stage of the growth process. The impact on the Ga grading in the deposited layer was measured by SIMS. The position and slope of the Ga grading profiles were optimized for high efficiency solar cells. Effects on the phases found in the absorber layer were investigated by Raman spectroscopy. The recorded spectra show the formation of a group III rich phase in layers grown at high maximum Cu contents. Best PV parameters were achieved for solar cells developed with absorbers grown with [Cu]/[In + Ga] = 1.05 at the end of the 2nd stage.