Effects of substrate characteristics on the passivation performance of ALD-Al₂O₃ thin film for high-efficiency solar cells

Atom layer deposition (ALD)-Al₂O₃ thin films are considered effective passivation layers for p-type silicon surfaces. A lower surface recombination rate was obtained through optimizing the deposition parameters. The effects of some of the basic substrate characteristics including material type, bulk resistivity and surface morphology on the passivation performance of ALD-Al₂O₃ are evaluated in this paper. Surface recombination velocities of 7.8 cm/s and 6.5 cm/s were obtained for p-type and n-type wafers without emitters, respectively. Substrates with bulk resistivity ranging from 1.5 to 4 Ω·cm were all great for such passivation films, and a higher implied V_oc of 660 mV on the 3 Ω·cm substrate was achieved. A minority carrier lifetime (MCL) of nearly 10 μs higher was obtained for cells with a polished back surface compared to those with a textured surface, which indicates the necessity of the polishing process for high-efficiency solar cells. For n-type semi-finished solar cells, a lower effective front surface recombination velocity of 31.8 cm/s was acquired, implying the great potential of (ALD)-Al₂O₃ thin films for high-efficiency n-type solar cells. (semiconductor devices)