Low recombination p(+) and n(+) regions for high performance silicon solar cells

The results of research on p(+) and n(+) doping are presented. Ion implantation has been used to obtain nearly optimal values of peak dopant concentration in the highly-doped regions. It is found that if the doping concentration is carefully limited, n(+) and p(+) regions that are transparent to minority carrier flow can be attained. It is shown that these regions are quite sensitive to surface recombination velocity and that surface passivation must be used to obtain high conversion efficiency. Data are presented that indicate that recombination at the metal-silicon contact interface limits Voc when passivated transparent regions are utilized. Recent solar cell results are presented. Collection efficiency near unity is demonstrated. High Voc has been obtained with both n(+)-p-p(+) cells (640 mV) and p(+)-n-n(+) structures (657 mV). Efficiency is in excess of 18 percent, not only for float zone but also for Czochralski silicon.