Spatially resolved defect diagnostics in multicrystalline silicon for solar cells

Scanning room temperature photoluminescence (PL) spectroscopy was applied to cast multicrystalline Si to assess the electronic properties of high-quality solar-grade material. The intensity of band-to-band emission with the maximum at 1.09 eV positively correlates with minority carrier lifetime measured concurrently using the laser-microwave reflection technique. A point-by-point mapping revealed the linear dependence of the band-to-band PL intensity and lifetime across entire multicrystalline-Si wafers. We have also found at room temperature an intense ‘defect’ PL band with the maximum at about 0.8 eV in wafer regions with a low band-to-band emission and degraded lifetime. The PL mapping of the 0.8 eV band intensity revealed a linkage to areas of a high dislocation density. Dislocation topography was obtained independently using light scattering technique and mapping the dislocation D-lines at 77 K. PL spectroscopy down to 4.2 K was performed at areas with high and low ‘defect’ band intensity. The origin of the 0.8 eV band is discussed in a connection with dislocations in multicrystalline Si. We demonstrate advantages of scanning room temperature PL spectroscopy for in-line diagnostics of Si-based materials.