Structural properties and quality of the photoexcited state in Cu(In1−xGax)Se2 solar cell absorbers with lateral submicron resolution

We analyze the quality of the photoexcited state in Cu(In,Ga)Se2 absorbers prepared under conditions similar to module pilot line production with different Ga-admixtures in terms of the splitting of the quasi-Fermi levels by confocal microscopic photoluminescence (PL) with submicron lateral resolution. The lateral luminescence patterns exhibit structures in the length scale of some micrometers (3–10 μm) which by far exceed the geometrical sizes of individual grains with diameters of 1 μm or below, detected simultaneously by optical reflection, and by scans of atomic force microscopy (AFM). The luminescence yields recorded at (83–250) K and at about (104–102) air mass 1.5 (AM1.5)-equivalent photon fluxes show lateral alterations by factors (2–20) depending on Ga-content, excitation level, and temperature. From temperature and excitation regimes, we are able to extrapolate the lateral variations towards 300 K and AM1.5-equivalent fluxes, and we translate PL-yields into lateral alterations of the splitting of quasi-Fermi-levels Δ(EFn−EFp) and of corresponding variations in maximum hypothetic open circuit voltages Voc.