High efficiency screen-printed EFG Si solar cells through rapid thermal processing-induced bulk lifetime enhancement

This paper shows that one second (1 s) firing of Si solar cells with screen-printed Al on the back and SiNx anti-reflection coating on the front can produce a high quality Al-doped back-surface-field (Al-BSF) and significantly enhance SiNx-induced defect hydrogenation in the bulk Si. Open-circuit voltage, internal quantum efficiency measurements, and cross-sectional scanning electron microscopy pictures on float-zone silicon cells revealed that 1 s firing in rapid thermal processing at 750°C produces just as good a BSF as 60 s firing, indicating that the quality of Al-BSF region is not a strong function of RTP firing time at 750°C. Analysis of edge-defined film-fed grown (EFG) Si cells showed that short-term firing is much more effective in improving the hydrogen passivation of bulk defects in EFG Si. Average minority-carrier lifetime in EFG wafers improved from ∼3 to ∼33 μs by 60 s firing but reached as high as 95μs with 1 s firing, resulting in 15·6% efficient screen-printed cells on EFG Si.