We examine the carrier lifetime evolution of block-cast multicrystalline silicon (mc-Si) wafers under illumination (100 mW/cm2) at elevated temperature (75°C). Samples are treated with different process steps typically applied in industrial solar cell production. We observe a pronounced degradation in lifetime after rapid thermal annealing (RTA) at 900°C. However, we detect only a weak lifetime instability in mc-Si wafers which are RTA-treated at 650°C. After completion of the degradation, the lifetime is observed to recover and finally reaches carrier lifetimes comparable to the initial state. To explain the observed lifetime evolution, we suggest a defect model, where metal precipitates in the mc-Si bulk dissolve during the RTA treatment.

The interstitial iron concentration in multicrystalline silicon wafers, determined from recombination lifetime measurements, is effectively reduced by annealing the wafers at very low temperature (300–500 °C). During annealing, the iron concentration decreases by more than one order of magnitude. The observed disappearance of interstitial iron is explained by internal gettering of the iron by crystallographic defects.

We use photoluminescence (PL) measurements by a silicon charge‐coupled device camera to generate high‐resolution lifetime images of multicrystalline silicon wafers. Absolute values of the excess carrier density are determined by calibrating the PL image by means of contactless photoconductance measurements. The photoconductance setup is integrated in the camera‐based PL setup and therefore identical measurement conditions are realised. We demonstrate the validity of this method by comparison with microwave‐detected photoconductance decay measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the emission of light from industrial multicrystalline silicon solar cells under forward and reverse biases. Camera-based luminescence imaging techniques and dark lock-in thermography are used to gain information about the spatial distribution and the energy dissipation at pre-breakdown sites frequently found in multicrystalline silicon solar cells. The pre-breakdown occurs at specific sites and is associated with an increase in temperature and the emission of visible light under reverse bias. Moreover, additional light emission is found in some regions in the subband-gap range between 1400 and 1700 nm under forward bias. Investigations of multicrystalline silicon solar cells with different interstitial oxygen concentrations and with an electron microscopic analysis suggest that the local light emission in these areas is directly related to clusters of oxygen.

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