POTENTIAL AND LIMITATIONS OF EPITAXIAL EMITTERS

摘要

Reducing the total costs of modules by increasing the efficiency of solar cells is one of the major challengesin today’s photovoltaic research. The emitter epitaxy by atmospheric pressure chemical vapour deposition (APCVD) offers acost-efficient and faster alternative to the standard furnace diffusion pr°Cess. The epitaxial emitter formation at 1050 °C onlytakes 1-2 min whereas the diffusion pr°Cess using P°Cl3 takes up to 60 min. The purpose of this work is to show the potentialof epitaxial grown emitters compared to diffused emitters. PC1D simulations show an increase in voltage of V°C = + 10 mVand a reduction in saturation current J0e of 30% for the epitaxial emitter. These advantages are due to lower surfacerecombination vel°City and reduction of Auger recombination of the optimised emitter profile. The lifetime experimentsincluding an epitaxial emitter show a diffusion length Leff of 750 μm and an emitter saturation current of J0e = 46 fA/cm² on aplanar 10 cm p-type FZ wafer. Another important aim of this work is to determine the limitations of epitaxial emitters due tothermal degradation of the base material, interface recombination and the change of reflective properties on textured wafersdue the deposition pr°Cess. In a first batch, solar cell efficiencies up to 18.4 % underline that emitter epitaxy by APCVD is acompetitive pr°Cess for the emitter formation.