Passivation and carrier selectivity of TiO 2 contacts combined with different passivation layers and electrodes for silicon solar cells
Date
2017
Authors
Boccard, Mathieu
Yang, Xinbo
Weber, Klaus
Holman, Zachary C
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Volume Title
Publisher
IEEE Xplore
Abstract
Titanium dioxide (TiO2) films have previously
been demonstrated to function as electron-selective contacts to
silicon solar cells, and an efficiency of 21.6% has been reported
for a cell featuring a full-area TiO2 contact. However, the
passivation quality of TiO2 contacts still falls short of that
possible with best-in-class contacts based on, e.g., hydrogenated
amorphous silicon (a-Si:H). We investigate here the performance
of a-Si:H/TiO2 stacks as electron-selective, passivating contacts.
We show that combining a-Si:H with TiO2 can result in excellent
surface passivation (lifetime close to 3 ms for textured CZ
wafers), especially for 7.5-nm-thick TiO2 capping layers.
However, initial cell results show that such a-Si:H/TiO2 stacks
give poorer efficiencies than TiO2 only, with extremely low fill
factors due to S-shaped current-voltage curves. Also, the role of
the rear electrode becomes apparent when substituting Al for an
ITO/Ag stack: the latter has significantly lower open-circuit
voltage and fill factor than the former. Combining a TiO2/Al rear
electron contact (with no a-Si:H) and an intrinsic a-Si:H/p-type aSi:H front hole contact, we demonstrate a double heterojunction
silicon solar cell with an efficiency of approximately 15%.
Furthermore, a full metal-oxide heterojunction cell that combines
a molybdenum oxide (MoOx)/ITO hole contact with the TiO2/Al
electron contact achieves an efficiency of 11%.
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Conference Record of the IEEE Photovoltaic Specialists Conference
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Conference paper
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2099-12-31