Aluminium electrode induced surface passivation deterioration for dopant free passivated contacts

Abstract

This paper reports that current widely used metal electrode aluminum results in dramatic passivation deterioration of some dopant-free passivated contacts (DFPC) (e.g. TiOx/LiFx， a-Si/LiFx and a-Si/TiOx/LiFx) after the Al electrode is deposited on the DFPC, which significantly lowers the device performance since excellent surface passivation is one of the key requirements for the successful integration of a full area contact in a solar cell. More interestingly, we find that the Al electrode thickness has a significant impact on the passivation deterioration. A thin Al (10nm) electrode results in the most severe passivation degradation for TiOx/LiFx. The thin TiOx behaves as a sacrifice layer in an a-Si/TiOx/LiFx contact improving the passivation stability upon thermal treatment. The presented result in this study implies that the passivation performance of a passivated contact assessed based on a the widely usage of nanometer-scale metal film on DFPC to mimic a metalized device structure is not fully reliable for evaluating the contact surface passivation quality, and instead a metal layer replicating the final intended device should be implemented, in combination to PL analysis for the extraction of the passivation quality.