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

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3.2.2.1 Seff dependence on Dit. Low Seff of the PECVD SiΝ X :H-passiνated Si surface is
attributed to the combining of moderately low density of interface states, and a high
positive charge density. Both parameters are given in Table 2.1 for as-deposited and
thermally treated silicon nitride films [68].
According to the SRH formalism, Seff will decrease by reducing the interface state
density D1. In Figure 3.6, the dependence of Seff on Dit is shown for Ι Ω-cm p-Si wafer.
Figure 3.6 Calculated effective surface recombination velocity Seff for p-Si surface as a
function of the injection level Δn in the quasi-neutral bulk for different values
of interface state density Dit. Input parameters: Doping concentration = 1 x 10 16
em-3 ; o;, = 1 x 10 -14cm2, σn =1 x 10 -16cm2; Qf= 1.3 x 10 11 cm -2 .
Experimental results are consistent with this prediction. As can be seen from
Figure 3.7, SiΝ :H films prepared by remote plasma or direct PECVD at high frequency
(HF) provide much better surface passivation than nitride layers prepared at low
frequency (LF). This is achieved by avoiding heavy ion bombardment during the
deposition process, and consequently much lower Di t [56].