Investigation of intragrain defects in pc-Si layers obtained by aluminum-induced crystallization: Comparison of layers made by low and high temperature epitaxy

Abstract

Thin-film polycrystalline-silicon (pc-Si) solar cells with a grain size in the order of 1–100 μm could substantially lower the price of photovoltaic energy if sufficiently high efficiencies are obtained on low-cost foreign substrates. A promising approach is the epitaxial thickening of seed layers made by aluminum-induced crystallization (AIC) of amorphous silicon. A clear difference in performance was found for AIC based solar cells grown by low- and high-temperature epitaxy. A large intragrain defect density was observed for this type of pc-Si solar cells that probably limits the cell performance. This paper studies intragrain defect formation in AIC based pc-Si layers by the investigation of state of the art absorber layers grown both by low- and high-temperature epitaxy on seed layers made on various substrates. The samples were characterized by defect etching in combination with scanning electron microscopy (SEM) and by cross-section transmission electron microscopy (TEM). The AIC seed layers themselves were found to be major sources of intragrain defects. Moreover, AIC seed layers prepared under different conditions can lead to different intragrain defect densities.