Optimized amorphous silicon oxide buffer layers for silicon heterojunction solar cells with microcrystalline silicon oxide contact layers

We report on the systematic optimization of the intrinsic amorphous silicon oxide buffer layer in interplay with doped microcrystalline silicon oxide contact layers for silicon heterojunction solar cells using all silicon oxide based functional layers on flat p-type float-zone wafers. While the surface passivation quality is comparably good within a wide range of low oxygen contents, the optical band gap increases and the dark conductivity decreases with increasing oxygen content, giving rise to an inevitable trade-off between optical transparency and electrical conductivity. On the cell level, fill factor FF and short circuit current density J(sc) losses compete with the open circuit voltage V-oc gains resulting from a thickness increase of the front buffer layers, whereas J(sc) and V-oc gains compete with FF losses resulting from increasing thickness of the rear buffer layers. We obtained the highest active area efficiency of eta(act) = 18.5% with V-oc = 664mV, J(sc) = 35.7mA/cm(2), and FF = 78.0% using 4 nm front and 8nm rear buffer layer with an oxygen content of 5%. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4798603]