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The structural and optical properties of two solar cells in which the Cu2ZnSnS4 absorber layer was sulphurized by two different methods (S flux and graphite box), were studied. The grain sizes are dependent on the sulphurization method, the larger ones being obtained for the sulphurization in a S flux. The optical properties were investigated by photoluminescence (PL). A broad and asymmetric band was observed for the sample with the larger grains, whereas for the other one a very broad emission was obtained, mostly influenced by the CdS buffer layer. The dependence on the excitation power revealed the influence of fluctuating potentials created by strong doping and high compensation of the absorber layer. Radiative recombination channels are quite different from the ones typical of semiconductor materials with flat bands. A relationship between the PL intensity from the absorber layer measured at low temperatures, and the final PV performance is established. Thus, we propose that PL can be used as an evaluation experimental technique in order to decide if a certain absorber should be processed into a full solar cell or not.

Until this day, the most efficient Cu(In,Ga)Se2 thin film solar cells have been prepared using a rather complex growth process often referred to as three-stage or multistage. This family of processes is mainly characterized by a first step deposited with only In, Ga and Se flux to form a first layer. Cu is added in a second step until the film becomes slightly Cu-rich, where-after the film is converted to its final Cu-poor composition by a third stage, again with no or very little addition of Cu. In this paper, a comparison between solar cells prepared with the three-stage process and a one-stage/in-line process with the same composition, thickness, and solar cell stack is made. The one-stage process is easier to be used in an industrial scale and do not have Cu-rich transitions. The samples were analyzed using glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction, current–voltage-temperature, capacitance-voltage, external quantum efficiency, transmission/reflection, and photoluminescence. It was concluded that in spite of differences in the texturing, morphology and Ga gradient, the electrical performance of the two types of samples is quite similar as demonstrated by the similar J–V behavior, quantum spectral response, and the estimated recombination losses.