(Georgia Institute of Technology, 2005-01)
Meemongkolkiat, Vichai; Nakayashiki, Kenta; Rohatgi, Ajeet; Crabtree, Geoffrey; Nickerson, Jeff; Jester, Theresa L.
A systematic study of the variation in resistivity and lifetime on cell performance, before and after light-induced
degradation (LID), was performed along the B- and Ga-doped Czochralski (Cz) ingots. Screen-printed solar cells with Al-back surface field were fabricated and analyzed
from different locations on the ingots. Despite the large variation in resistivity (0.57 Ω-cm to 2.5 Ω-cm) and lifetime
(100-1000 μs) in the Ga-doped Cz ingot, the efficiency variation was found to be ≤ 0.5%. No LID was observed in the cells fabricated from the Ga-doped ingot. In contrast
with the Ga-doped ingot, the B-doped ingot showed a very tight resistivity range (0.87 Ω-cm to 1.22 Ω-cm), resulting in very tight lifetime and efficiency distributions. However, the LID effect reduced the efficiency of these B-doped cells by about 1.1% absolute. Additionally, the use of
thinner substrate and higher resistivity B-doped Cz is shown to effectively reduce the LID effect.
(Georgia Institute of Technology, 2005-01)
Crabtree, Geoffrey; Jester, Theresa L.; Fredric, Christian; Nickerson, Jeff; Meemongkolkiat, Vichai; Rohatgi, Ajeet
Results of efforts at Shell Solar to implement the use of gallium dopant as a commercial solar cell production process are presented. Both small area cell results and
production related activities and results are discussed. Many researchers have demonstrated that gallium effectively eliminates light induced degradation (LID) of
the bulk lifetime, but less effort has been dedicated to implement gallium dopant into a commercial production process. Shell Solar has worked in this direction and expanded past research activities to demonstrate that
the full range of resistivity values produced from a gallium-doped crystal can be used to successfully fabricate high efficiency cells. In addition, Shell has
produced significant numbers of gallium-doped cells in their production facility and characterized process
results from crystal growth to module build. This paper discusses additional subjects essential to production viability, such as gallium metal availability, silicon
feedstock availability and management specific to a gallium process and overall cost effectiveness.