Recombination in ingot cast silicon solar cells

Abstract

Minority carrier recombination is studied in multicrystalline ingot cast silicon solar cells. The normalized recombination strength Gamma of dislocations is obtained by correlating topograms of the internal quantum efficiency (IQE) with those of the dislocation density rho. Gamma is obtained by fitting an extended theory of Donolato to the experimental data. The measured Gamma-values vary significantly between adjacent dislocation clusters and correlate with the spatial pattern of the dislocations. All Gamma-values are strongly dependent on the parameters of the solar cell process. The influence of phosphorus diffusion and hydrogenation is shown. After solidification of the silicon, impurities from the crucible enter the ingot and deteriorate its border regions during cooling to room temperature. These deteriorated border regions can be significantly improved by an additional low temperature anneal that is applied after phosphorus diffusion. The experiments indicate that the mechanism of the anneal is external phosphorus gettering into the emitter

Grain boundary effect on lifetime in high performance multicrystalline silicon during solar cell processing

“…Both gettering and hydrogenation will, if used separately, deteriorate the wafer electrical performance in the middle of the ingot. This HPMCSi behaviour is different from the results presented by Karzel et al for a standard multicrystalline wafer, where gettering resulted in increasing values relative to the ungettered state, but is in agreement with observations by other works on mc-Si [6,7,13]. Improvement of lifetime only by gettering is obtained in the bottom of the ingot, at 6% of the ingot height.…”

“…Recombination activity of both grain boundaries and dislocations has been shown to correlate to the level of impurity content in the material [4,5]. Conventional multicrystalline silicon has been studied extensively in regard to changes in defect recombination activity during solar cell processing [6][7][8]. Two main process steps affecting this mechanism are phosphorus diffusion gettering and hydrogenation.…”

Precipitated iron: A limit on gettering efficacy in multicrystalline silicon

“…Similar results indicating little change in ironsilicide precipitates during extended low-temperature annealing have been found previously. 33,48 D. Using As-grown iron-silicide precipitate distribution data to predict interstitial iron concentrations after gettering…”

Recombination at Lomer Dislocations in Multicrystalline Silicon for Solar Cells

“…In particular, there is a long lasting discussion whether the low lifetime in the poor crystallographic quality regions is caused by more or less randomly distributed dislocations (e.g., [5], [42] and [43]), or by recombination-active GBs (e.g., [44]- [46]). A particular role is played here by smallangle grain boundaries (SAGBs).…”