Analyses of Local Open Circuit Voltages in Polycrystalline Cu(In,Ga)Se2 Thin Film Solar Cell Absorbers on the Micrometer Scale by Confocal Luminescence

Abstract

Polycrystalline chalcopyrite absorbers in thin film solar cells exhibit distinct spatial inhomogeneities which are obviously introduced during growth of the grainy structure. Amongst several structural inhomogeneities in scale lengths of grains of one ?m or below, spatial variations of optoelectronic properties in much larger scales of some ?m can be observed, such as fluctuations in the splitting of quasi-Fermi levels in the range of several tens of meV. These have been quantitatively deduced via Planck's generalized law from spectrally resolved confocal room temperature luminescence scans. Since the necessary absorption length in thin film semiconductors is in the neighborhood of the wavelength of photons, for the evaluation of luminescence spectra wave optics with multireflection effects have been applied.