The Effect of Bifacial AlOx Deposition on PERC Solar Cell Performance

Single-sided atomic layer deposition (ALD) is challenging as often some degree of wrap-around deposition onto the nontarget side occurs. This is particularly challenging for aluminum oxide (AlO
_x
) deposition on silicon solar cells, as is required on the rear of passivated emitter rear cell (PERC) solar cells. The effects of unintended ALD-deposited AlO
_x
on the front side of PERC solar cells are explored in this work, with a specific focus on the impact on contact resistance. The contact resistance is determined from transmission line measurement structures on samples with up to 10 nm of AlO
_x
on top of silicon nitride (SiN
_x
). These values are used as input parameters for computer simulations to simulate the effect of varying degrees of wrap-around on p-PERC cells. Finally, p-type aluminum back surface field solar cells with 3, 5, 7, and 10 nm AlO
_x
layers on top of the SiN
_x
are fabricated using various firing recipes and screen printing pastes to assess the effect on fabricated devices. It was found that a 3 nm AlO
_x
layer can improve the cell performance relative to the uncapped case, whereas 5, 7, and 10 nm resulted in a lower solar cell efficiency due to higher series resistance.