Extensive investigations on industrial multicrystalline silicon solar cells have shown that, for standard 1 X cm material, acid-etched texturization, and in absence of strong ohmic shunts, there are three different types of breakdown appearing in different reverse bias ranges. Between À4 and À9 V there is early breakdown (type 1), which is due to Al contamination of the surface. Between À9 and À13 V defect-induced breakdown (type 2) dominates, which is due to metal-containing precipitates lying within recombination-active grain boundaries. Beyond À13 V we may find in addition avalanche breakdown (type 3) at etch pits, which is characterized by a steep slope of the I-V characteristic, avalanche carrier multiplication by impact ionization, and a negative temperature coefficient of the reverse current. If instead of acid-etching alkaline-etching is used, all these breakdown classes also appear, but their onset voltage is enlarged by several volts. Also for cells made from upgraded metallurgical grade material these classes can be distinguished. However, due to the higher net doping concentration of this material, their onset voltage is considerably reduced here.

In this paper, we present new insight in the degradation and subsequent recovery of charge carrier lifetime upon light soaking at 75 °C observed in float-zone silicon wafers. Variations of doping type, dielectric passivation schemes and thermal treatments after layer deposition were performed. The degradation was only observed for p-type float-zone silicon wafers passivated with passivation schemes involving silicon nitride layers. An influence of thermal treatments after deposition was found. N-type wafers did not degrade independent of their passivation scheme. Room temperature re-passivation experiments showed the degradation to affect the wafer bulk, and photoluminescence studies demonstrated fine lateral striations of effective lifetime. We conclude that the degradation is caused by bulk defects that might be related to hydrogen complexes

This paper discusses degradation phenomena in crystalline silicon. We present new investigations of the light-and elevated temperature-induced degradation of multicrystalline silicon. The investigations provide insights into the defect parameters as well as the diffusivity and solubility of impurity species contributing to the defect. We discuss possible defect precursor species and can rule out several metallic impurities. We find that an involvement of hydrogen in the defect could explain the characteristic observations for light-and elevated temperature-induced degradation. Furthermore, we demonstrate analogies to the light-induced degradation mechanisms at elevated temperatures observed in floatzone silicon, where several experimental results also indicate an involvement of hydrogen in the defect. Based on the similarities between multicrystalline and floatzone silicon, we suggest that both degradation phenomena might be caused by the same or similar defects. As we do not expect large concentrations of metals in floatzone silicon, we suggest that complexes of hydrogen and a species introduced during crystal growth might cause both degradation phenomena.

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Light‐ and elevated temperature‐induced degradation in multicrystalline silicon can reduce the efficiency of solar cells significantly. In this work, the influence of the firing process and its temperature profile on the degradation behaviour of neighbouring mc‐Si wafers is analysed. Five profiles with measured high peak temperatures ≥800 °C and varying heating and cooling ramps are examined. With spatially resolved and lifetime calibrated photoluminescence images, normalized defect concentrations N*t are calculated to determine the degradation intensity. Wafers that underwent a fast firing process typical for industrial solar cell production show a significantly stronger degradation than samples that were subjected to the same peak temperature but with slower heating and cooling rates. A spatially resolved analysis of the carrier lifetime in the whole wafer shows that the degradation begins in low lifetime areas around dislocation clusters, spreading into good grains after several hours. By the use of optimized ramp‐up and/or ramp‐down rates during the firing even at very high peak temperatures, light and elevated temperature induced degradation can be suppressed. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)