Characterization and application of rapid thermal oxide surface passivation for the highest efficiency RTP silicon solar cells

This paper presents the development and analysis of the first 19%-efficient silicon solar cells fabricated by rapid thermal processing (RTP). These cells required no high-temperature conventional furnace processing (CFP). Improved front surface passivation by rapid thermal oxidation (RTO) was found to reduce S_front from 7.5×10 ⁵ to 2×10⁴ cm/s, decrease J_0e by almost an order of magnitude, and increase cell efficiency by about 1% (absolute). An additional 1% gain in efficiency was achieved by applying a thicker screen-printed, RTP-alloyed Al-BSF instead of the standard 1 μm evaporated Al-BSF. Because of the rapid heating rate in RTP, the RTP Al-BSF also gives a more uniform and effective BSF compared with the CFP Al-BSF. In comparison with furnace processed cells, this RTP/RTO process reduced the time for diffusion and oxidation from 330 to 10 min without sacrificing efficiency. To reduce back surface recombination further, RTO can be grown on the back. PCD characterization of RTO on 1.3 Ωcm Si reveals an S_back well below 100 cm/s, which can result in >20% efficient RTP/RTO cells