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Epitaxial n- and p-Type Emitters for High Efficiency Solar Cell Concepts

: Rachow, T.

Journal of Energy and Power Engineering 8 (2014), S.1371-1377
ISSN: 1934-8975
ISSN: 1934-7367
Fraunhofer ISE ()
Materialien - Solarzellen und Technologie; Silicium-Photovoltaik; Kristalline Silicium-Dünnschichtsolarzellen; Formation; Epitaxy; Based Deposition

Reducing the module prices by increasing the efficiency of solar cells is one of the major challenges in today’s photovoltaic research. The emitter formation by epitaxial growth offers a cost-efficient and faster alternative to the standard furnace diffusion process. The efficiency potential of epitaxial emitters > 22% has already been proven using a single wafer, low pressure, chemical vapour deposition tool. The purpose of this work is to show the potential of epitaxially grown emitters by APCVD (atmospheric pressure chemical vapour deposition) compared to diffused emitters. The APCVD formation of epitaxial emitters at 1,050 °C can be realised as high throughput inline process and only takes 1-2 min, whereas the diffusion process using POCl3 takes up to 60 min. Simulations show an increase in voltage of DVOC = +10 mV and a reduction in saturation current J0 of 30% for the epitaxial emitter. The lifetime experiments of solar cells with epitaxial emitter exhibit a diffusion length Leff > 750 µm and an emitter saturation current of J0e < 50 fA/cm² on a planar 10 Wcm p-type FZ wafer. Another important aim of this work is to evaluate the limitations of epitaxial emitters due to high thermal budget, interface recombination and the change of reflective properties on textured wafers due to the deposition process. Solar cell efficiencies up to 18.4% on p-type and 20.0% on n-type wafers presented in this paper underline that the emitter epitaxy by APCVD is a competitive process for the emitter formation.