“Compared to the previous results imec reported, we have further optimized the fully screen printed bifacial n-PERT cell process and adopted a design with 12 busbars. The current cells also have a screen printed front grid and rear soldering pads that use less silver,” said Loic Tous, project leader at imec/EnergyVille. “The open circuit voltage (Voc) is now above 690mV with fill factors up to 83%. These remarkable results are obtained using the same industry-compatible equipment to produce bifacial p-PERC cells, with the addition of boron diffusion.”
A batch of 12 new M2-sized cells (244.3 cm²) measured at ISFH CalTec showed an average conversion efficiency of 23.0 percent, with the best cell topping 23.2%, and measurements revealed a bifaciality above 80%. Moreover, used under standard front illumination conditions in conjunction with an additional 0.15 sun rear illumination, the cells can achieve an effective conversion efficiency of almost 26 percent. In addition, ISFH CalTec measured an average reverse current of -0.4A (at -12V) indicating excellent breakdown characteristics.
The developed n-PERT technology has a number of inherent advantages over p-type PERC cell technology, which is demonstrated in these newest cells: the potential for higher efficiencies because of lower sensitivity to metal impurities, and the absence of light-induced degradation (LID). Therefore, n-type PERT technology could become a cost-effective contender for p-type PERC cells. To enable this, the current cells have a screen printed front grid and rear soldering pads which together amounts to less than 80mg of silver used per cell.
Imec and Jolywood are confident that their bifacial n-PERT cells will soon reach efficiencies above 23.5 percent, coupled to a bifaciality above 90%.
“Jolywood targets to bring the best solar solution to the market," said Jia Chen, R&D director at Jolywood. "Devoted to R&D and manufacturing of the world’s best n-type cells and modules, we believe n-type technology can contribute to the industry with high performance, high reliability and low LCOE. We have chosen imec to help us reach that target because of their unique expertise and research infrastructure. We are also developing bifacial n-PERT cells with passivating contact technology, and have already achieved efficiencies above 23%. Combining all the technical know-how, we are confident that our bifacial n-type solar cells will achieve an efficiency above 24% very soon.”