Helium versus hydrogen dilution in the optimization of polymorphous silicon solar cells

• Published in: Journal of non-crystalline solids Vol. 338; no. Complete; pp. 668 - 672
• Main Authors: Tchakarov, S., Das, Debajyoti, Saadane, O., Kharchenko, A.V., Suendo, V., Kail, F., Roca i Cabarrocas, P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-06-2004
• Subjects: A205; T310; 81.20.−n; 81.05.−t; S270
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2004.03.068

We have studied how the increase of pressure in the deposition of polymorphous silicon can reduce the ion energy and the damage of the p-layer in p–i–n solar cells. By increasing the pressure during the deposition of the i-layer to 3 Torr, we have been able to increase the fill factor and the solar cell efficiency up to 8.4%. In an attempt to reduce the optical gap and increase further the deposition rate we have studied the use of He dilution. Changing the dilution from hydrogen to He leads to a higher deposition rate at lower rf power while keeping similar transport properties. Moreover, the lower hydrogen content of He diluted films results in a smaller band gap and a higher short circuit current in solar cells. Thus, silane-He mixtures allow to reduce the ion energy for a constant deposition rate and to minimize the damage at the p-layer and p/i interface. The cells show a fill factor of 0.69,
V
oc of 0.91 V, an initial efficiency of 9.3% on textured SnO
2.