Imec, Crystal Solar Achieve Solar Cell Efficiency

Nanoelectronics research center Imec of Leuven, Belgium, and direct wafer developer Crystal Solar have reported 22.5 percent cell efficiency with nPERT silicon solar cells manufactured on 6-in. mono-crystalline epitaxially grown kerfless wafers.

Crystal Solar's epitaxial system. Courtesy of Crystal Solar.

The companies cite this demonstration as the highest efficiency to date for homojunction solar cells on epitaxially grown silicon wafers, paving the way toward the technology’s industrialization.

“The combination of our advanced cell process and the innovative wafer manufacturing technique of Crystal Solar is paving the way for manufacturing of highly efficient solar cells at substantially lower cost and will be disruptive for the complete solar manufacturing value chain,” said Jozef Szlufcik, director of Imec’s photovoltaic department.

Crystal Solar’s Direct Gas manufacturing technology enables direct conversion of feedstock gas to mono crystalline silicon wafers by high throughput epitaxial growth. By skipping the polysilicon, ingoting and wire-sawing steps, the approach results in lowest cost and enables the growth of high-quality p-n junction in-situ.

Imec's solar cell. Courtesy of Imec.

Imec adapted its nPERT silicon solar cell process to align with the properties of Crystal Solar’s kerfless wafers. The cells were fabricated on 160- to 180-μm thick grown n-type wafers with built-in rear p+ emitter. Imec's n-PERT process included a selective front surface field realized by laser doping, advanced emitter surface passivation by Al₂O₃ and Ni/Cu plated contacts. The novel process resulted in a 22.5 percent record efficiency for homojunction large-area solar cells and a record open circuit voltage of 700 mV.

"We are pleased to see such a high conversion efficiency on our epitaxially grown n-type wafers with built in boron-doped junctions,” said T.S. Ravi, CEO of Crystal Solar. "We expect to achieve >23 percent efficiencies with Imec’s PERT technology in the very near future.”