Electrical activity of intragrain defects in polycrystalline silicon layers obtained by aluminum-induced crystallization and epitaxy

Abstract

Defect etching revealed a very large density (∼109cm−2) of intragrain defects in polycrystalline silicon (pc-Si) layers obtained through aluminum-induced crystallization of amorphous Si and epitaxy. Electron-beam-induced current measurements showed a strong recombination activity at these defects. Cathodoluminescence measurements showed the presence of two deep-level radiative transitions (0.85 and 0.93eV) with a relative intensity varying from grain to grain. These results indicate that the unexpected quasi-independence on the grain size of the open-circuit voltage of these pc-Si solar cells is due to the presence of numerous electrically active intragrain defects.

Thin-film polycrystalline silicon solar cells with low intragrain defect density made via laser crystallization and epitaxial growth

“…This we attributed to a high density of electrically active intragrain defects (IGD) [3,4]. In figure 1 a SEM image of the interior of a single grain in the pc-Si layer, obtained via AIC and epitaxial growth, is shown after defect etching.…”

Thin-film monocrystalline-silicon solar cells made by a seed layer approach on glass-ceramic substrates

“…Besides the many grain boundaries (the average grain size is typically around 10 mm), the polycrystalline-silicon layers typically show an intragrain-defect density of around 10 8 -10 9 cm À2 [7]. From a crystallographic point of view, the monocrystalline layers therefore have a much better quality than the polycrystalline layers.…”

“…With AIC in combination with thermal CVD, pc-Si cell efficiencies of up to 8.0% and 6.4% were reached on opaque alumina and transparent glass-ceramic substrates, respectively [1,2]. Although the AIC process enables the fabrication of pc-Si layers with large grains [3][4][5][6], the limited structural and electronic quality of the AIC seed layers was found to be one of the main cell-efficiency-limiting factors [7][8][9]. Higher cell efficiencies can therefore be obtained by improving the AIC seed layer quality or by using a different method to fabricate the seed layer.…”

High performance plasma hydrogenation for large-grained polycrystalline silicon thin film solar cells

“…Improving the material quality is essential for poly-Si to become a more competitive technology. Possibility to improve material lies in better crystallographic quality, which includes increasing grain size and decreasing intra grain defect density [2]. Plasma hydrogenation is one of commonly used methods to achieve this improvement by passivating grain boundaries, dislocations and point defects in polycrystalline silicon thinfilm solar cells [3,4].…”