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To date, Al2O3 passivation on p-type Si (p-Si) via atomic layer deposition (ALD) has demonstrated the highest quality surface passivation of any non-native dielectric. Recent work has also shown that such passivation can out-perform conventional diffused-dopant back surface field (BSF) layers via a fixed-charge field effect. As such, Al2O3 passivation has become one of the de facto approaches used in commercial Si solar cells. Implementing such an ALD-Al2O3 rear passivation scheme into our group's existing GaAsP/Si tandem solar cell design thus has the potential to increase overall device efficiency by 1-2% absolute (or approaching ~10% relative), as well as bring at least some of the fabrication processes closer to incumbent technologies. However, we do not currently have an established process for this desirable structure. Therefore, the research described herein sought to develop a baseline process for rear p-Si solar cell passivation via ALD-Al2O3, with subsequent electrical contacting, that is compatible with the GaAsP/Si structure. This work included investigation of key process variables / conditions, quantification of the passivation quality metrics related to those conditions, and initial efforts toward optimization of the process for maximized cell efficiency.