Factors influencing the minority carrier diffusion length in multicrystalline silicon produced in a HEM furnace

The heat exchange method (HEM) process has been used to produce ingots up to 80 kg in weight. The minority carrier diffusion length of ingots has been measured principally by the time-resolved microwave reflectance technique to determine the factors limiting the diffusion length. Feedstock selection is important, but boron doping plays only a minor role. Intra-grain crystallographic defects appear to limit diffusion length strongly. Under optimized conditions a minority carrier diffusion length of 230 μm at 1 Ω-cm resistivity has been achieved. Solar cell efficiencies of up to 12.7% have been achieved in production