Optimized Temperature in Phosphorous Diffusion Gettering Setup of Chromium Transition Metal in Solar Grade Multicrystalline p-Type Silicon Wafer

Abstract

We have investigated in this work the effect of the temperature profile during homogeneous phosphorous diffusion gettering (PDG) on multicrystalline (mc-Si) silicon p-type wafers destined for photovoltaic solar cells. Temperatures were varied from 800 • C due probably to a partial dissolution of the metallic precipitates, especially at the grain boundaries and in the dislocations vicinity. The related τCr-Impurity lifetime value of about 8.5 µs is extracted, which is the result of interstitial Cri or CriBs pairs, proving their strongest recombination activity in silicon.

Synchrotron-based analysis of chromium distributions in multicrystalline silicon for solar cells

“…14 Sch€ on et al found that minority carrier lifetime increased and [Cr i ] decreased after phosphorous diffusion gettering. 13 Other quantitative studies of the effect of phosphorous diffusion gettering have measured high chromium concentrations at near-surface regions, suggesting external gettering, [15][16][17] as well as a reduction of the total bulk chromium concentration. 18 For this study, two adjacent (sister) wafers were selected from a 12 kg laboratory-scale intentionally chromiumcontaminated mc-Si ingot.…”

“…13,[15][16][17][18] Lifetimes (Cr i , Dn ¼ 10 15 cm À3 ) and interstitial concentrations as measured by quasi-steady-state photoconductance (QSSPC) before and after gettering are shown in Fig. 3.…”

“…The remaining chromium (%10 13 cm À3 assuming no change in precipitate size or density) is likely externally gettered, diffusing to the emitter and PSG layer as has been observed by SIMS. [15][16][17] With one-half of the total Cr concentration in precipitated form, a diffusion temperature of %990 C (Cr solubility equal to 4 Â 10 13 cm À3 ) would be required to fully dissolve precipitates.…”