A disruptive technology for the solar industry

25th April 2016
Joe Bush

A specialist in direct wafer growing technologies for the next generation of solar photovoltaic products, Crystal Solar, and Imec have achieved a 22.5% cell efficiency (certified by FhG ISE CalLab) with nPERT silicon (Si) solar cells manufactured on six inch mono-crystalline epitaxially grown kerfless wafers, which will help to pave the way toward industrialisation of this promising technology.

Crystal Solar’s breakthrough manufacturing technology called Direct Gas to Wafer enables direct conversion of feedstock gas to mono-crystalline silicon wafers by high throughput epitaxial growth. By skipping the polysilicon, ingoting and the wire sawing steps altogether, this approach not only results in low cost/watt for the wafers but also reduces the capital required to set-up a manufacturing plant. Furthermore, an ability of this kerfless process is that the p-n junctions required for solar cell fabrication can be grown in-situ.

Imec has adapted its nPERT Si solar cell process to align with the properties of Crystal Solar’s kerfless wafers. The 156x156mm2 cells were fabricated on 160 to 180um thick grown n-type wafers with built-in rear p+ emitter. Imec’s n-PERT process included a selective front surface field realised by laser doping, advanced emitter surface passivation by Al2O3 and Ni/Cu plated contacts. The novel process using all industrially available processing steps resulted in record efficiencies for homojunction large area solar cells of 22.5% and a record Voc of 700mV.

Jozef Szlufcik, PV Department Director at Imec, commented: “We are extremely happy to have achieved such high conversion efficiencies on nPERT solar cells processed from kerfless wafers using Imec’s pre-pilot industrial silicon PV manufacturing line. The combination of our advanced cell process and the innovative wafer manufacturing technique of Crystal Solar, is paving the way to the manufacturing of highly efficient solar cells at lower cost than currently possible. Using these kerfless wafers will be disruptive for the complete solar cell manufacturing value chain.”

“We are pleased to see such a high conversion efficiency on our epitaxially grown kerfless n-type wafers with built-in born doped junctions”, said T.S. Ravi, CEO of Crystal Solar. “The epitaxial direct wafer growth with built-in junctions approach represents a new paradigm in cell manufacturing with its unique ability to bypass significant steps in both wafer and cell manufacturing thereby dramatically reducing the capex and the overall cost per watt. We expect to achieve >23% efficiencies with IMEC’s PERT technology in the very near future”, Ravi concluded.

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