21.0% record efficiency for large area (156 × 156 mm2) n-type EWT solar cell

At the 37th IEEE Photovoltaic Specialist Conference, which took place in Seattle in June 2011, ISFH and Q-Cells already presented small n-type EWT solar cells with an efficiency of 21.6% and an area of (20 × 20) mm2. The cell process is based on monocrystalline Czochralski n-type silicon.

The boron-doped emitter is defined with laser structuring and is passivated optimally with an aluminumoxide-siliconnitride double layer. ISFH has now scaled up the solar cell production processes to large wafer formats. A novel back contact design with four busbars has been developed, which reduces the finger length to about 50 mm and makes it possible to realize on this large cell area a metalization with a solar cell resitivity contribution less than 0.5 Ohm·cm2.

The project team at ISFH with project manager Till Brendemühl and the R&D team at Q-Cells SE are particularly pleased with the performance of the best (156 × 156) mm2 area solar cell, which has an efficiency of 21.0%, a Jsc of 40.5 mA/cm2, a Voc of 667 mV, and a fill factor of 77.7%.

The solar cells have been measured with a class A sun simulator in the characterization lab at Q-Cells SE, using a measuring chuck developed at ISFH. The measurement has been corrected considering the spectral mismatch.

“This cell type still has the potential for further improvements. We are confident to reach even higher efficiencies” says physicist Fabian Kiefer, who is developing back-contacted solar cells as part of his PhD thesis.

“Our goal is to simplify the production process significantly, while keeping the efficiencies above 21.0% on large cell area” says Prof. Dr. Nils-Peter Harder, head of the group.