Flat-plate solar array project process development area process research of non-CZ silicon material

Three sets of samples were laser processed and then cell processed. The laser processing was carried out on P-type and N-type web at laser power levels from 0.5 joule/sq cm to 2.5 joule/sq cm. Six different liquid dopants were tested (3 phosphorus dopants, 2 boron dopants, 1 aluminum dopant). The laser processed web strips were fabricated into solar cells immediately after laser processing and after various annealing cycles. Spreading resistance measurements made on a number of these samples indicate that the N(+)P (phosphorus doped) junction is approx. 0.2 micrometers deep and suitable for solar cells. However, the P(+)N (or P(+)P) junction is very shallow ( 0.1 micrometers) with a low surface concentration and resulting high resistance. Due to this effect, the fabricated cells are of low efficiency. The maximum efficiency attained was 9.6% on P-type web after a 700 C anneal. The main reason for the low efficiency was a high series resistance in the cell due to a high resistance back contact.