Module-level Cell Processing of Silicon Heterojunction Interdigitated Back-Contacted (SHJ-IBC) Solar Cells with Efficiencies above 22%: Towards All-Dry Processing

Abstract

Module-level processing of silicon heterojunction interdigitated back-contacted (SHJ-IBC) solar cells while bonded to glass, in the so-called i2-module concept, is discussed. In this approach, a key challenge is the interdigitated patterning of aSi:H without compromising on the rear-surface passivation. Process adaptations involving more resistant bonding agents and a milder wet etchant enabled bonded cells with the best efficiency of 21.7% and VOC of 734 mV, which are the highest reported for bonded cells processed partially at module level, and which undoubtedly proves the potential of this i2-module concept to reach high Voc and efficiency. Yet another challenge is to make the process flow cost-effective and industrially-relevant, i.e. a lithofree, all-dry process flow, analogous to thin-film PV module fabrication. As a first step, dry etching of a-Si:H was developed to replace wet etching, and was successfully incorporated in a SHJIBC process flow to fabricate freestanding cells with the best efficiency of 22.9% and above 20% on thick (190 μm) and thin (56 μm) EVA-bonded silicon.