Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 35: Poster I

HL 35.21: Poster

Dienstag, 8. März 2016, 15:00–19:00, Poster A

In situ TEM investigations of the back surface field of aluminum in multi-crystalline silicon — •Hendrik Spende, Patrick Peretzki, and Michael Seibt — IV. Physikalisches Institut der Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen

The rear contact of a solar cell requires a uniform low-resistance ohmic contact, minority-carrier reflection, photon reflection and effective gettering of impurities while processing. Standard solar cells use alloyed backside contacts because of their positive effect on the cell efficiency. Screen printing or evaporating Al on the silicon wafer and thermal annealing lead to the formation of an aluminum alloyed back surface field (Al-BSF) at the Al-Si interface. This creates a heavily Al doped p+-region, which forms a pn-junction with the n-type Si, or a p+/p- junction reducing backside recombination.

The formation of the Al-BSF and the effect of grain boundaries in n-type multicrystalline silicon (mc-Si) - used here for preparation issues - were studied by in situ transmission electron microscopy. The grain boundaries were made visible by etching with HNO₃ and HF, then Al was evaporated onto the surface and lamellas were prepared by FIB. During heating the temperature was increased above the eutectic point of Al and Si. The Si dissolved into the Al and then the Al penetrated the Si wafer. During cooling Si doped with Al recrystallized and left a doped BSF region.