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Paper on solar cell passivation

Al2O3 nanolayers grown by ALD contain negative fixed charges. Electrical measurements on slant-etched layers reveal that these charges are located within 1 nm distance to the interface with the Si substrate.

When inserting additional interface layers, the fixed charge density can be continuously adjusted from 3.5·1012 cm‑2 (negative polarity) to zero and up to 4.0·1012 cm‑2 (positive polarity). An HfO2 interface layer of one monolayer or more reduces the negative fixed charges in Al2O3 to zero. Based on the good passivation properties of this charge-free HfO2/Al2O3 stack, negative or positive fixed charges can be formed by introducing additional thin Al2O3 or SiO2 layers between the Si substrate and this HfO2/Al2O3 capping layer. All stacks provide very good passivation of the silicon surface. The measured effective carrier lifetimes are between 1 and 30 ms. This charge control in Al2O3 nanolayers allows the construction of zero fixed charge passivation layers as well as layers with tailored fixed charge densities for future solar cell concepts and other field-effect based devices.

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