Evaluation and Assessment of the ASPIRE Concept: A New Integrated mc-Si Cell and Module Design for High-Efficiencies

Current bottlenecks for industrial application of Al2O3 deposited by Atomic Layer Deposition (ALD) on open rear passivated solar cells are low growth rate, firing stability of thin and uncapped layers, and Firing-through BSF formation during co-firing. Long term stability results on the performance of a high throughput ALD prototype , the Levitrack, are presented. Excellent passivation properties have been obtained after firing: for 12 nm thick films deposited on p-Fz (1.8 Ω.cm) a τeff of 2.2 ms (Δn=3x10 15 cm-3) was obtained that remained constant over a period of 20 weeks. Furthermore, we report on the passivation quality of the firing-through BSF and Al 2 O 3 coating as function of wafer peak temperatures between 790 and 845°C. Bifacial cells covered for 50% Al contacts resulted in local BSF thicknesses of 5 to 7 µm and FF of 78% and 77% for the best mc and mono crystalline cell respectively. For this study 12 nm uncapped aluminum oxide layers are deposited on the rear of p-type mc and mono bifacial cells. LBIC measurements confirm literature reports that uncapped Al 2 O 3 passivation in general is heavily dependent on the wafer peak temperatures during firing in the investigated range.

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Improved performance of uncapped Al<inf>2</inf>O<inf>3</inf> and local firing-through Al-BSF in Bi-facial solar cells

Cesar

Mewe

Granneman³

et al. 2012

2012 38th IEEE Photovoltaic Specialists Conference

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Silicon solar cells that dominate today's market are H-pattern cells based on p-type silicon wafer material with a full Al Back Surface Field (BSF) as rear contact. ECN's rear passivated bi-facial PASHA (Passivated on all sides H-pattern) and ASPIRe (All Sides Passivated and Interconnected at the Rear, MWT) concepts answer the market pressure to decrease the euro/watt price and increase the efficiency. For optimized cells we estimate 0.5-0.8% absolute higher cell efficiencies compared to the industrial standard due to better rear passivation and reflection, while thinner wafers <150um) can be processed with limited yield loss. In addition, Al paste consumption can be reduced by 50-70% owing to the open rear metallization. Here we report on the improved performance of PASHA cells passivated by an uncapped Al 2 O 3 layer on the rear, through which Al paste is fired for contact and local aluminum BSF formation. The Al 2 O 3 dielectric layer is deposited in the Levitrack, an industrial-type system for high-throughput Atomic Layer Deposition (ALD) developed by Levitech. On Cz and mc material, a gain in J sc xV oc of 1% and 2.5% respectively is obtained compared to the reference, at a rear metal fraction of 30%. Localized IQE mapping shows that the passivation quality of the Al 2 O 3 passivation layer is maintained after firing which is a major improvement as compared to our previous report. Furthermore, reliability tests on single cell laminates (Cz cells) suggest that the passivation layer remains stable during the lifetime of a module.

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Evaluation and Assessment of the ASPIRE Concept: A New Integrated mc-Si Cell and Module Design for High-Efficiencies

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Effect of Al Contact Pitch on Rear Passivated Solar Cells

Effect of Al Contact Pitch on Rear Passivated Solar Cells

Industrial application of uncapped Al<inf>2</inf>O<inf>3</inf> and firing-through Al-BSF in open rear passivated solar cells

Improved performance of uncapped Al<inf>2</inf>O<inf>3</inf> and local firing-through Al-BSF in Bi-facial solar cells

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