Understanding carrier trapping in multicrystalline silicon

Abstract

The physical origin of minority carrier trapping centers in multicrystalline silicon is explored in both gettered and non-gettered material. The experimental evidence suggests that there are two types of trap present. One species can be removed by gettering and is related to the presence of boron}impurity pairs or complexes. The other type is impervious to gettering and is correlated to the dislocation density. Annealing experiments reveal that the trapping centers caused by boron}impurity complexes can be dissociated, and that these trapping centers do not contribute to recombination. The e!ect of trapping centers on open-circuit voltage is shown to be negligible when the trap density is less than the dopant density.

Ga co‐doping in Cz‐grown silicon ingots to overcome limitations of B and P compensated silicon feedstock for PV applications

“…However, because of the lower segregation coefficient of phosphorus (0.35) compared to that of boron (0.8), the net doping is not uniform along the ingot height and inversion of Si polarity, from p-to n-type may occur during crystallization, reducing the material yield for industrial solar cell fabrication. Simulations [5] using Scheil's law for dopant distribution and simple models for calculating carrier mobility show that requiring a minimum resistivity of 0.5Ω.cm and an ingot yield of at least 90% compels the use of Si feedstock containing less than 0.45 ppmw of B and 1.0 ppmw of P. Gallium co-doping has recently been proposed [6][7][8] as a potential solution to control the C l along the ingot height even when using Si containing large quantities of B and P. It relies on the low segregation coefficient of Ga which enables the increased P concentration, in relation to B, to be counterbalanced during crystal growth. It is thus possible to obtain low net doping and p-type resistivity along the full ingot height.…”

Trapping behavior of Shockley-Read-Hall recombination centers in silicon solar cells

“…From the injection density where the symptomatic rise of the apparent lifetime occurs, we can conclude that there are more traplike defects in the not-fired sample than in the fired sample. 28 Additionally, the fired sample shows a higher recombination Figure 5.…”

Solar cells from upgraded metallurgical-grade silicon purified by metallurgical routes

“…Three different gettering processes (1, 2, and 3) were adopted based on gettering processes used for polycrystalline silicon. [30][31][32][33][34] The main purpose of this experiment was to investigate which gettering process is most appropriate for monocrystalline UMG-Si. The basic differences between the three gettering processes were the temperature (850 C or 900 C) and the annealing times.…”

“…The beneficial effect of using a lower temperature, compared with the conventional temperature of 900 C, has already been reported for multicrystalline silicon. [30][31][32] At the higher temperature (900 C), some trapped impurities are redistributed within the UMG-Si, which degrades the final g. This effect is partially reduced by adopting the lower temperature of 850 C. Fig. 6 shows the g of several solar cells fabricated from UMG-Si and commercial silicon wafers (Table II).…”