Surface and bulk passivation of multicrystalline silicon solar cells by ...

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the passivation of dangling bonds at the SiN-silicon interface with the following possible
reaction pathways:
(i) A hydrogen radical in the plasma gas attaches to a Si dangling bond and forms
a Si-H bond:
Si° + .Η --> =Si—Η
(ii) Silane radicals react with the surface:
Si° + ·Si—Η2--> =Si—Si—Η2
(iii) A Si—H+ ion from the plasma attaches to a Si dangling bond by forming a
weak bridging Si—H +—Si bond. One of the Si atoms then forms a Si—Si bond with a
neighboring Si dangling bond at the silicon surface by hopping of an electron:
Si—H+ + .Si 0 --> =Si—Η+ Si,
Si—H+ —Si= + =Si° + / - =Si—Si= + =Sι—Η
From the above model, it can be seen that .Η radical plays a fundamental role in
the formation of complexes.
2.5.2 Hydrogen Passivation Effect
Although the mechanism of bulk passivation of c-Si solar cells by SiΝ :Η films is not yet
completely known, the passivation effect has been experimentally proved. Chen et. al.
[71] studied PECVD of SiΝx films (-600 A) on top of PECVD-grown SiO2 (400 A) on
both surfaces of samples followed by photo-assisted anneal at 350°C in forming gas
ambient. The bulk and surface passivation effects were quantified and decoupled by a
combination of internal quantum efficiency (IQE) measurements and computer modeling.