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imec ups silicon solar cell efficiency to 22%

15 Jan 2015

R&D group uses laser doping to boost efficiency of large area industrial crystalline-silicon n-PERT design.

Nano-electronics research center imec has announced that it has improved its large area n-type PERT (passivated emitter, rear totally diffused) crystalline silicon solar cell on 6inch n-type Cz-Si wafers, now reaching a top conversion efficiency of 22.02% (calibrated, as previously, at the Fraunhofer ISE CalLab).

This is the highest efficiency achieved for this type of two-side-contacted solar cell on an industrial large area wafer size. This incremental but sigificant improvement in performance builds upon the 21.5% conversion efficiency for a similar structure that imec achieved in July 2014, as reported by optics.org.

Imec says that compared to p-type silicon solar cells, n-type cells do not suffer from light induced degradation and feature a higher tolerance to common metal impurities. As a result, n-type silicon solar cells are considered as promising alternatives to p-type solar cells for “next generation” highly efficient solar cells.

Laser doping

With the aim of increasing the conversion efficiency of its large-area n-PERT silicon cells using advanced industrial processes, imec says it has further improved the conversion efficiency of its n-PERT solar cell, reaching a record 22%, featuring an open-circuit voltage of 684mV, a short-circuit current of 39.9mA/cm2, and 80.7% fill factor. Efficiency improvements were obtained by the introduction of a selective front surface field through laser doping, giving a boost in open circuit voltage and short circuit current.

Filip Duerinckx, manager of imec’s n-PERT technology platform, commented, “Our new developments, resulting in additional improvement of the conversion efficiency, further confirm the potential of n-type PERT cells for next-generation highly efficient silicon solar cells. This new efficiency record has been achieved while simultaneously simplifying the process, relying only on simplified cleans and without any expensive Forming Gas Anneal. We are committed to further increasing the efficiency of this cell concept and adding to the industrial value of the technology. This will enable bringing this technology to the market in short term.”

Imec’s n-PERT silicon solar cells feature Ni/Cu/Ag front contacts, applied using an industrial plating tool from Meco Equipment Engineers, and rear local contacts obtained by laser ablation of the rear passivation stack and subsequent metallization. The rear passivation stack includes a thin (<10 nm) Atomic-Layer-Deposited (ALD) Al2O3 layer, deposited with the spatial ALD technique InPassion Lab from SoLayTec.

About the Author

Matthew Peach is a contributing editor to optics.org.

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