Oxygen-Related Defect Centers in Solar-Grade, Multicrystalline Silicon. A Reservoir of Lifetime Killers
✍ Scribed by D. Karg; G. Pensl; M. Schulz; C. Hässler; W. Koch
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 159 KB
- Volume
- 222
- Category
- Article
- ISSN
- 0370-1972
No coin nor oath required. For personal study only.
✦ Synopsis
Dedicated to Professor Dr. Wolfgang Schro È ter on the occasion of his 65th anniversary
The effective lifetime of charge carriers t eff in multicrystalline silicon (mc-Si) Baysix 1 wafers (in our case: Bridgman-type) cut from areas close above the ingot bottom is reduced (t eff < 1 ms). However, the efficiency of solar cells processed on such bottom-near Baysix 1 wafers is comparable to that one of solar cells processed on Baysix 1 wafers taken from the middle of the ingot. In order to clarify this unusual behavior, specially casted, low-doped n-and p-type mc-Si ingots, respectively, were fabricated by Bayer AG and were studied by optical and electrical characterization techniques. It is demonstrated that the decrease of the effective lifetime t eff in as-grown wafers originating from a region directly above the ingot bottom is caused by oxygen-related Thermal Donors (TDs), Shallow Thermal Donors (STDs) and O1-/O2-defects as well as by low concentrations ( 1.5 Â 10 12 cm ± ±3 ) of vanadium and chromium impurities. Most of the oxygen-related defect centers are thermally dissociated by the solar cell process resulting in comparable efficiencies as obtained for wafers taken from the middle of the ingot. D. Karg et al.: Oxygen-Related Defect Centers in Solar-Grade, Multicrystalline Silicon