Influence of Room Temperature Sputtered Al-Doped Zinc Oxide on Passivation Quality in Silicon Heterojunction Solar Cells

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Al-doped zinc oxide (AZO) is a potential candidate to substitute tin-doped indium oxide in silicon heterojunction (SHJ) solar cells due to its low cost and low ecological impact. The AZO, sputtered at room temperature (RT), is of particular interest because of low thermal budget and potential for high throughput production with the well-established industrial methods. In SHJ solar cells, high effective carrier lifetime prerequisite for the high open-circuit voltage is achieved with surface passivation by intrinsic amorphous silicon layers followed by doped silicon layers. The passivation quality may be affected by the subsequent sputtering of an AZO layer especially at RT. In this article, we investigated the influence of the AZO sputtering and postdeposition annealing on the effective carrier lifetime in symmetrical silicon layer stacks with n- or p-type doped silicon layers and solar cell precursors. It has been found that the effective carrier lifetime significantly decreased after AZO sputtering at RT. The detrimental effect of AZO sputtering is substrate temperature dependent and is smaller or even absent at elevated temperatures. However, postdeposition annealing, equivalent to the Ag paste curing, mostly recovered the effective carrier lifetime in the symmetrical stacks as well as in the cell precursors. Finally, an aperture area efficiency of 21.2% has been achieved for the 19 mm × 19 mm SHJ solar cell prepared with room temperature sputtered AZO.