Stable passivation of cut edges in encapsulated n-type silicon solar cells using Nafion polymer

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigi-tated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be repassivatedafter cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L & C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 degrees C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.

Automated summary

This study investigates the effectiveness and stability of Nafion polymer edge passivation in n-type interdigitated back contact (IBC) solar cells. Different edge types and cutting techniques are evaluated, and it is found that thermal laser separation (TLS) and mechanical cleaving enable good repassivation on both emitter and back surface field (BSF) edges. The impact of edge repassivation on cell performance is assessed, and an efficiency improvement is observed for cells with emitter edges but not for cells with BSF edges. The stability of the Nafion repassivation in real-world conditions is also evaluated, revealing its stability in ethylvinylacetate (EVA) encapsulants but not in polyolefin elastomer (POE).