Gettering and passivation techniques for quality enhancement of multicrystalline silicon

Conference · Thu Jun 30 00:00:00 EDT 1994 · AIP Conference Proceedings (American Institute of Physics); (United States)

OSTI ID:7256378

Rohatgi, A; Chen, Z; Sana, P; Evers, N; Ramanachalam, R; Doolittle, A ^[1]

---

1. School of Electrical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

A detailed investigation of quality enhancement techniques, such as PECVD SiO[sub 2]/SiN and forming gas anneal (FGA) for defect passivation, and Al and P diffusion for defect and impurity gettering, was conducted on promising PV multicrystalline Si materials. In selected cases FZ single crystal Si was used as baseline. It was found that PECVD SiO[sub 2] followed by photo-assisted anneal can result in extremely low surface recombination velocity ([lt]2 cm/s) on 500 [Omega]-cm FZ wafers, and very low interface state density (1--5[times]10[sup 10] eV[sup [minus]1] cm[sup [minus]2]) on 10 [Omega]-cm FZ wafers. The PECVD SiO[sub 2]/SiN coating increases the effective lifetime by a factor of 2 to 10, and decrease the surface recombination by a factor of 5--22, depending upon the multicrystalline material. Al treatment was found to getter process-induced as well as grown-in defects and impurities by providing a sink near the Al/Si interface. This is in addition to the BSF and light trapping effect of Al treatment. Presence of high stress or dislocation density in the material was found to enhance the gettering efficiency of the Al process. A 930 [degree]C phosphorus diffusion followed by an etch back was found to be optimum for emitter formation in multicrystalline Si cells, which resulted in high bulk lifetime without significant penalty from the heavy doping effects. PECVD SiO/SiN passivation of cast material increased bulk lifetime in the solar cell from 10 [mu]s to 20 [mu]s, and decreased the front surface recombination velocity from 2[times]10[sup 5] cm/s to 5[times]10[sup 4] cm/s. Finally, FGA in conjunction with Al treatment improved EFG Si cells efficiency by 5.3%, with 2.6% improvement resulting from the FGA alone, 1.5% from Al gettering alone, and 1.2% from Al diffusion and FGA interaction.

• OSTI ID: 7256378
• Report Number(s): CONF-9310273-; CODEN: APCPCS
• Journal Information: AIP Conference Proceedings (American Institute of Physics); (United States), Vol. 306:1; Conference: 12. National Renewable Energy Laboratory (NREL) photovoltaic program review, Denver, CO (United States), Oct 1993; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
14 SOLAR ENERGY
SILICON
PASSIVATION
ALUMINIUM ADDITIONS
CHEMICAL VAPOR DEPOSITION
CRYSTAL DEFECTS
GETTERING
PHOSPHORUS ADDITIONS
QUANTUM EFFICIENCY
SILICON NITRIDES
SILICON OXIDES
SILICON SOLAR CELLS
STRESSES
ALLOYS
ALUMINIUM ALLOYS
CHALCOGENIDES
CHEMICAL COATING
CRYSTAL STRUCTURE
DEPOSITION
DIRECT ENERGY CONVERTERS
EFFICIENCY
ELEMENTS
EQUIPMENT
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
PNICTIDES
SEMIMETALS
SILICON COMPOUNDS
SOLAR CELLS
SOLAR EQUIPMENT
SURFACE COATING
360602* - Other Materials- Structure & Phase Studies
140501 - Solar Energy Conversion- Photovoltaic Conversion