Role of O-2 radicals on silicone plasma treatments for a-Si:H surface passivation of PV wafers bonded to glass

Abstract

Argon (Ar) and oxygen (O-2) plasmas are performed on silicone adhesives to eliminate the negative influence of silicone on amorphous silicon (a-Si: H) surface passivation of wafers bonded to glass. Both the Ar and O-2 plasmas lead to oxidation of the silicone surface, consisting in an increase of oxygen/carbon ratio, of degree of crosslinking, and of material density. The oxidized silicone is more resilient than pristine and does not interact with the a-Si: H passivation process, allowing for state-of-the-art surface passivation of wafers bonded to glass. Similarities between the modifications induced by the Ar and O-2 plasmas on the silicone indicate the secondary role of the O-2 radicals in the oxidation process. Moreover, amorphous/crystalline heterojunction interdigitated back contact solar cells (a-Si: H/c-Si HJ i-BC) are fabricated on freestanding and bonded wafers treated with Ar plasma. The devices show comparable open-circuit voltages of up to 675 mV, confirming at device level the efficacy of the treatment. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim