UV Stability of Aluminum Oxide Fabricated with Tube-Type Plasma-Enhanced Atomic Layer Deposition

Ultraviolet (UV)-induced degradation is a critical issue for modern photovoltaic (PV) technologies such as passivated emitter and rear cell (PERC), tunnel oxide-passivated contact (TOPCon), and heterojunction (HJT) cell concepts. This study compares the stability against UV radiation of AlO_x/SiN_y stacks on mini-modules with p-type back junction solar cells. Our cells have a nondiffused textured front surface passivated with an AlO_x/SiN_y layer stack and feature passivating polysilicon on oxide rear contacts. We compare plasma-enhanced chemical vapor deposition (PECVD) and plasma-enhanced atomic layer deposition (PEALD) processes for the deposition of AlO_x layers using the same tube-type deposition system. After a UV dose of 146 kWh/m² using broadband UV lamps, modules with PECVD-AlO_x exhibit an efficiency loss of up to 27% while those with PEALD-AlO_x show minimal degradation of 2.5%. This comparison proves that the superior UV stability is achieved with the tube-type PEALD technique. Our findings thus show how UV stability can be improved without extra equipment dedicated solely to depositing ALD-AlO_x and without UV absorbing or down converting encapsulants.