| Popis: |
Measurements of the dislocation density are compared with locally resolved measurements of carrier lifetime for p-type multicrystalline silicon. A correlation between dislocation density and carrier recombination was found: high carrier lifetimes (> 100 mu s) were only measured in areas with low dislocation density (< 10(5)cm(-2)), in areas of high dislocation density (> 10(6) cm(-2)) relatively low lifetimes (< 20 mu s) were observed. In order to remove mobile impurities from the silicon, a phosphorus diffusion gettering process was applied. An increase of the carrier lifetime by about a factor of three was observed in lowly dislocated regions whereas in highly dislocated areas no gettering efficiency was observed. To test the effectiveness of the gettering in a solar cell manufacturing process, five different multicrystalline silicon materials from four manufacturers were phosphorus gettered. Base resistivity varied between 0.5 and 5 Omega cm for the boron- and gallium-doped p-type wafers which were used in this study. The high-efficiency solar cell structure, which has led to the highest conversion efficiencies of multicrystalline silicon solar cells to date, was used to fabricate numerous solar cells with aperture areas of 1 and 4 cm(2). Efficiencies in the 20% range were achieved for all materials with an average value of 18%. Best efficiencies for 1 cm(2) (20.3%) and 4cm(2) (19.8%) cells were achieved on 0.6 and 1.5 Omega cm, respectively. This proves that multicrystalline silicon of very different material specification can yield very high efficiencies if an appropriate cell process is applied. |
