Enhanced passivation for silicon solar cells by anodic aluminum oxide

Previously, we proposed a novel rear contacting scheme comprising a porous anodic aluminum oxide (AAO) layer for forming point rear contacts to silicon solar cells. In this paper, we report that, if the rear-side AAO layer is formed over an intervening dielectric layer of either SiN_x or thermally-grown SiO₂, then high minority carrier lifetimes are possible. Using photoconductance decay measurements implied V_OC values of over 685 mV and 700 mV were recorded for SiO₂/AAO and SiN_x/AAO dielectric stacks for rear surface passivation, respectively when used in conjunction with 3 Ω cm p-type CZ silicon wafers with an n-type diffused emitter. The thickness of the SiO₂ and SiN_x intervening layers was 140 and 75 nm, respectively. These promising results suggest that the AAO self-patterning localised rear contacting approach may be possible without any loss in passivation quality, and, in fact, with some potential of improved V_OC values.