UV Stable Passivation Stack with Plasma-Enhanced Atomic Layer Deposition of Aluminum Oxide from an Industrial Tube-Type Direct Plasma-Enhanced Chemical Vapor Deposition System

We implement the plasma-enhanced atomic layer deposition (PEALD) of AlOx layers in an industrial tube-type plasma-enhanced chemical vapor deposition (PECVD) system with a direct plasma source. Its surface passivation qualities on the boron-diffused textured surface of n-type silicon wafers and on the undiffused textured surface of p-type silicon wafers are investigated by varying the process parameters. The study shows that the number of ALD cycles is one of the essential parameters for achieving high passivation quality on the boron-diffused textured surface of n-type wafers. We achieve a surface recombination current density J0s of 3.6 fA/cm2 , extracted from lifetime measurements with a device simulation by considering a measured electrically active dopant depth profile. In contrast, the number of ALD cycles shows no impact on the surface passivation quality on the undiffused textured surface of ptype wafers. In both cases, we achieve a passivation quality which is on the same level as our reference with a PEALD AlOx layer, deposited with a lab-scale ALD tool. Our tube-type PEALD AlOx/PECVD SiNy passivation stack is integrated at the cell front side of a p-type back junction (BJ) solar cell featuring n+ -type passivating polysilicon on oxide (POLO) contacts. Its cell performance is on the same level as the reference group with PECVD AlOx/SiNy passivation stack. The UV stability is investigated by exposing cell precursors to ultraviolet light with a dose of 4.5 kWh/m². While the PECVD AlOx/SiNy passivation stack shows a significant degradation of the measured effective lifetime and the implied open-circuit voltage, the passivation quality of tube-type PEALD AlOx/PECVD SiNy passivation stack is stable.