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In-line processing of hot wire CVD a-SI:H solar cells using different ZnO:Al morphologies as front contact

: Sittinger, V.; Laukart, A.; Harig, T.; Höfer, M.; Dewald, W.; Britze, C.; Schäfer, L.; Szyszka, B.; Bräuer, G.


European Commission:
26th European Photovoltaic Solar Energy Conference and Exhibition, EU PVSEC. Proceedings : 5th to 9th September 2011 at the CCH - Congress Centre and International Fair Hamburg in Germany
München: WIP-Renewable Energies, 2011
ISBN: 3-936338-27-2
European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) <26, 2011, Hamburg>
Fraunhofer IST ()
thin film silicon solar cell; light trapping; transparent conductive oxide; hot-wire CVD; a-Si:H; ZnO; design of experiment (DOE)

Current developments show the possibility of a-Si:H solar cells reaching 10% stabilized efficiency with PECVD standard equipment. The morphology of the TCO front contact is a crucial component to reach high efficiencies in a-Si:H solar cells. Increased light trapping allows thinner i-layer and therefore reduced light induced metastability. Compared to the well-known SnO2:F films deposited by CVD, the ZnO:Al technology allows for better performance at low cost especially because ZnO:Al can be textured in order to enhance the light scattering into the cell. Besides increasing the efficiency by applying new TCO technologies a cost reduction for the fabrication of a-Si:H solar cells can be achieved by applying hot-wire CVD (HWCVD) technology for the deposition of the absorber structure. For the deposition of doped and intrinsic hydrogenated amorphous silicon (a-Si:H) films, we use an In-line HWCVD coating system with three deposition chambers, which are equipped with planar vertical multi wire arrays providing an activation area of 600 x 500 mm2. Using Design of Experiments (DoE), we have investigated the combined influence of the deposition process factors on the performance of i-a-Si:H and p-a-Si:H films. Results show that it is possible to achieve good microstructure for intrinsic a-Si:H films with deposition rates > 1.5 nm/s with silane gas consumption up to 90%. The most influential factor for resistivity of p-a-Si:H is the deposition pressure.