Rapid thermal processing: a comprehensive classification of silicon materials

Depending on the specific impurities and defect spectrum of a silicon material, the minority carrier lifetime can react diversely to rapid thermal processing (RTP). We have measured the lifetime of silicon materials before and after RTP and have diffused solar cells either by RTP or by conventional quartz tube furnace processing (CFP). Our investigations show that the lifetime of Fz-Si can be preserved during RTP resulting in up to 18.7 % efficient solar cells. For 1.4 Ωcm PV-grade Cz-Si, the stable lifetime after light degradation could be improved by up to 60 % by RTP. In the case of EFG-Si, the same average cell efficiency was obtained with RTP diffusion as with the industrial reference diffusion process. However, in the case of block-cast mc-Si, the lifetime decreases with increasing diffusion temperature indicating that P-diffusion in the second range might provide insufficient gettering.