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Light trapping in a-SI:H/µc-SI:H tandem solar cells on differently textured TCOS

: Dewald, W.; Feser, C.; Nowak, R.; Chakanga, K; Sergeev, O.; Sittinger, V.; Maydell, K. von


Nowak, S. ; European Commission:
27th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC 2012. DVD-ROM : Proceedings of the international conference held in Frankfurt, Germany, 24 - 28 September 2012
München: WIP-Renewable Energies, 2012
ISBN: 3-936338-28-0
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <27, 2012, Frankfurt>
Fraunhofer IST ()
light trapping; a-Si/µc-Si; ZnO; characterization

Different light trapping etch morphologies of ZnO:Al were used to fabricate a-Si:H\µc-Si:H tandem solar cells. The etched ZnO:Al was characterized by haze and angular resolved light scattering measurements as well as by AFM and SEM. The silicon growth was examined by Raman measurements at the wavelength of 488, 633 and 785 nm. Here a change in growth mode was observed depending on the underlying texture of the ZnO:Al, which means that the TCO structure not only improves light scattering but also alters the silicon growth. Several effects overlap when analyzing the performance of a solar cell: transmittance of the ZnO:Al, light scattering ability of the ZnO:Al morphology, subcell matching, crystallinity and defects of absorber and interfaces, parasitic absorption etc. The measured external quantum efficiency (EQE) is reduced by these factors. For optimization it is important to analyze them separately. In this paper the connection between short circuit current of the µc-Si:H bottom cell to the light scattering behavior is drawn, morphology is linked to the light trapping ability and silicon growth. Furthermore an H2 plasma treatment of the ZnO:Al before cell deposition boosts the bottom Jsc but reduces Voc.