Comparing n- and p-type polycrystalline silicon absorbers in thin-film solar cells

Deckers, Jan; Bourgeois, Emilie; Jivānescu, Mihaela; Abass, Aimi; Gestel, Dries Van; Nieuwenhuysen, Kris Van; Douhard, Bastien; D’Haen, Jan; Nesládek, Miloš; Manca, Jean; Gordon, Ivan; Bender, Hugo; Stesmans, André; Mertens, R.; Poortmans, Jef

doi:10.1016/j.tsf.2015.02.058

Cited by 5 publications

(1 citation statement)

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“…For most silicon devices, such as solar cells, light emitting diodes and thin film transistors, materials with low defect density are required, and precise control over the amount of impurities is needed for tuning the electronic properties. Point defects and grain boundaries decrease electronic mobility, and vacancies and dangling bonds may lead to electronic states close to the Fermi level that act as traps for photo-generated carriers in light emitting diodes and solar cells [1][2][3]. Epitaxial growth at low temperatures is a particularly promising avenue for silicon technology, as it can improve the interfacial abruptness and strain stability in heterostructures and prevent surface segregation or dopant diffusion [4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Ultrafast carrier dynamics and the role of grain boundaries in polycrystalline silicon thin films grown by molecular beam epitaxy

Titova

Cocker

et al. 2016

Semicond. Sci. Technol.

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We have used time-resolved terahertz spectroscopy to study microscopic photoconductivity and ultrafast photoexcited carrier dynamics in thin, pure, non-hydrogenated silicon films grown by molecular beam epitaxy on quartz substrates at temperatures ranging from 335 °C to 572 °C. By controlling the growth temperature, thin silicon films ranging from completely amorphous to polycrystalline with minimal amorphous phase can be achieved. Film morphology, in turn, determines its photoconductive properties: in the amorphous phase, carriers are trapped in bandtail states on sub-picosecond time scales, while the carriers excited in crystalline grains remain free for tens of picoseconds. We also find that in polycrystalline silicon the photoexcited carrier mobility is carrier-density-dependent, with higher carrier densities mitigating the effects of grain boundaries on inter-grain transport. In a film grown at the highest temperature of 572 °C, the morphology changes along the growth direction from polycrystalline with needles of single crystals in the bulk of the film to small crystallites interspersed with amorphous silicon at the top of the film. Depth profiling using different excitation wavelengths shows corresponding differences in the photoconductivity: the photoexcited carrier lifetime and mobility are higher in the first 100-150 nm from the substrate, suggesting that thinner, low-temperature grown polycrystalline silicon films are preferable for photovoltaic applications.

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