High-efficiency solar cells on phosphorus gettered multicrystalline silicon substrates

Abstract

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 ms) were only measured in areas with low dislocation density (<10 5 cm À2 ), in areas of high dislocation density (>10 6 cm À2 ) relatively low lifetimes (<20 ms) 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 0Á5 and 5 V 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 (20Á3%) and 4 cm 2 (19Á8%) cells were achieved on 0Á6 and 1Á5 V cm, respectively. This proves that multicrystalline silicon of very different material specification can yield very high efficiencies if an appropriate cell process is applied. HIGH EFFICIENCY mc-Si SOLAR CELLS 715 Ã Independent calibrated measurement at Fraunhofer ISE CalLab. y Independent calibrated measurement at NREL.

The Influence of the Base Material Parameters on Quantum and Photoconversion Efficiency of the Si Solar Cells

“…1). The same V oc behavior was observed for mc-Si with base resistivity in a range from 0.5 to 9.0 Wcm, after gettering process [15]. A characteristic feature of the solar cells mc-Si-2 and CzSi-2 with the sheet resistance of 45 Ω/□ is the highest value of FF, which results from greater depth and the value of the emitter dopant and finally the maximum values of shunt resistance for the fabricated cells in each series.…”

High-Efficiency Crystalline Silicon Solar Cells

“…Therefore, the investigation of electrically active defects is of great importance for photovoltaic material. Especially for multicrystalline silicon, it is very important to understand thermal treatments, gettering [12,50], and hydrogen passivation in order to increase the carrier diffusion length. These measures were extremely important to obtain the record efficiencies on small (20.3% on 1 cm 2 ) [14] and large area (18.1% on 137.7 cm 2 ) [51] multicrystalline substrates.…”

Competitive gettering of iron in silicon photovoltaics: Oxide precipitates versus phosphorus diffusion

“…6,7 They are however less effective at improving lifetime in the vicinity of decorated extended defects. [8][9][10] This suggests that the interaction between impurities and extended defects is either not fully overcome during gettering processes, or that the impurities re-segregate to the extended defects during cooling. Previous work has studied the effect of PDG on grain boundaries, 11,12 and findings are apparently contradictory with grain boundaries becoming more 12 or less 11 recombination active after gettering.…”