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We compare the recombination properties of three important types of multicrystalline silicon wafers for solar cells, namely conventionally-solidified p-type and n-type multicrystalline wafers, and also the recently developed 'high performance' p-type multicrystalline wafers. Three distinct regions of the wafers are examined in detail. These are the intra-grain regions, the grain boundaries, and the dislocation networks. The response of these regions to phosphorous gettering and hydrogenation are also characterised and compared. The electrical properties of intra-grain regions are assessed based on both the minority carrier lifetime and diffusion length. The recombination activities of grain boundaries are compared quantitatively in terms of their effective surface recombination velocities. The recombination behaviour of dislocations is evaluated qualitatively based on photoluminescence images. Our results show that the main performance limiting factors are likely to be recombination at crystal defects. Overall, grain boundaries in conventional p-type samples are more recombination active than those in high performance p-type and conventional n-type samples. The benefits of hydrogenation are most visible on n-type samples, leading to significant deactivation of most of the grain boundaries. As-grown grain boundaries and dislocations in high performance multicrystalline silicon tend not to be recombination active, and only become active after either gettering or hydrogenation.

We compare the recombination properties of grain boundaries in conventionally-solidified p-type, ntype and ‘high performance’ p-type multicrystalline silicon wafers in terms of their surface recombination velocities, and evaluate their response to phosphorus gettering and hydrogenation. Overall, grain boundaries in the conventional p-type samples were found to be more recombination active than those in the high performance p-type and conventional n-type samples. As-grown grain boundaries in high performance multicrystalline silicon were not recombination active and only became active after thermal processes. In contrast, grain boundaries in the n-type samples were already recombination active in the as-grown state, but show a dramatic reduction in their recombination strength after gettering and hydrogenation. Distinct sub-bandgap photoluminescence spectra were detected from grain boundaries that are already active before gettering, and also those activated by gettering, suggesting different origins for their recombination activities. Moreover, the detrimental influence of grain boundaries on solar cell devices is discussed with the aid of numerical simulations.

We compare the recombination properties of a large number of grain boundaries in multicrystalline silicon wafers with different contamination levels and investigate their response to phosphorous gettering and hydrogenation. The recombination activity of a grain boundary is quantified in terms of the effective surface recombination velocity SGB based on photoluminescence imaging and 2-D modeling of the emitted photoluminescence signal. Our results show that varying impurity levels along the ingot significantly impact the grain boundary behavior. Grain boundaries from the middle of the ingot become more recombination active after either gettering or hydrogenation alone, whereas grain boundaries from the top and bottom of the ingot have a more varied response. Hydrogenation, in general, is much more effective on gettered grain boundaries compared with as-grown grain boundaries. A close inspection of their injection dependence reveals that while some grain boundaries exhibit little injection dependence before gettering, others show a relatively large injection dependence, with their SGB increasing as the injection level decreases. The former type tend not to be recombination active after both gettering and hydrogenation and are less likely to impact the final cell performance, in comparison with grain boundaries of the latter type.

We present a method based on steady state photoluminescence (PL) imaging and modelling of the PL intensity profile across a grain boundary (GB) using 2D finite element analysis, to quantify the recombination strength of a GB in terms of the effective surface recombination velocity (S e f f). This quantity is a more meaningful and absolute measure of the recombination activity of a GB compared to the commonly used signal contrast, which can strongly depend on other sample parameters, such as the intra-grain bulk lifetime. The method also allows the injection dependence of the S e f f of a given GB to be explicitly determined. The method is particularly useful for studying the responses of GBs to different cell processing steps, such as phosphorus gettering and hydrogenation. The method is demonstrated on double-side passivated multicrystalline wafers, both before and after gettering, and single-side passivated wafers with a strongly non-uniform carrier density profile depth-wise. Good agreement is found between the measured PL profile and the simulated PL profile for both cases. We demonstrate that single-side passivated wafers allow more recombination active grain boundaries to be analysed with less unwanted influence from nearby features. The sensitivity limits and other practical constraints of the method are also discussed.

We present an approach to study the variation of the surface recombination velocity in multi-crystalline silicon wafers through photoluminescence imaging for thin, passivated and mirror polished wafers. The influence of crystal orientation on surface pass