Researchers at imec have achieved a new, record conversion efficiency for N-type PERT (Passivated Emitter, Rear Totally diffused) solar cells using Ni/Cu/Ag plating (3 bus bars grid) technology from Meco and Atomic Layer Deposited (ALD) Al2O3 process from SoLayTec.
Imec said that the large area wafer (156mm x 156mm) N-type PERT solar cell had calibrated at Fraunhofer ISE CalLab.
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“Notwithstanding the early development stage, the result shows very high efficiency potential of n-type PERT solar cells,” said Jozef Szlufcik, director of imec’s PV department. “Moreover, n-type cells remain unaffected by light induced degradation present in p-type cells due to Boron-Oxygen complex, which results in improved long-term energy yield and, therefore, lower total cost/kWh”.
The cell was said to have achieved an open circuit voltage (Voc) of 677mV, a short circuit current (Jsc) of 39.1 mA/cm2, and 81.3% fill factor, demonstrating the potential for improved conversion efficiencies with two side contacted crystalline silicon solar cells for volume commercial production.
The N-Type PERT cell was said to employ a rear blanket p+ emitter produced by boron diffusion with front metal contacts on an n+ front-surface-field formed by means of Ni/Cu/Ag plating from Meco.
The rear local contacts to the p+ emitter were said to have been produced by laser ablation of the rear passivation stack and subsequent physical-vapor-deposition of aluminum. The rear passivation stack includes a thin (<10 nm) ALD-based Al2O3 layer was deposited with SoLayTec’s spatial ALD technique in its ‘InPassion’ tool.
Roger Görtzen, co-founder and manager marketing and sales of SoLayTec told PV Tech: “It’s good to conclude that our industrial InPassion ALD is better than thermal Wet Oxide processing. This means that the ALD machine can be used for next generation cell concepts like e.g. PERC technology and for N-type passivation, without any changes in the hardware.”
The availability of low-cost N-type wafers are also seen as a critical part of the expected wider adoption of the substrate by mainstream solar cell producers in the coming years.