On the fixed charges in multifunctional doped APCVD layers for well passivated solar cells

Abstract

Silicate glass layers produced in atmospheric pressure chemical vapour deposition tools have shown to provide excellent surface passivation. For this, the field effect due to fixed charges in these layers plays an important role. In this contribution, we aim at separating the effect of glass properties, changing during the diffusion process, from the effect of the resulting dopant diffusion into the substrate. To this aim, we apply a short high temperature step that leads to negligible diffusion into the Si wafer but to glass properties that are similar to the ones obtained after the long high temperature process applied during solar cell manufacturing. We give an estimate for the measurement uncertainty that arises when the charges of such layers are measured after a short high temperature step, without the strong influence of a full band bending that would be caused by a deep high/low junction. In addition, the correlations between the density of fixed charges and the P content, the treatment temperature, as well as the associated passivation quality are shown. We also evaluate the chemical part of the passivation mechanism of the PSG layers when a SiNx:H is stacked on top. Excellent passivated surfaces with saturation current densities below 10 fAcm-2 can be achieved for the PSG/SiNx:H stack, exceeding the passivation quality of SiNx:H single layer reference samples.