Solar cell achieves high front side conversion efficiency

“Compared to the previous results imec reported, we have further optimised the fully screenprinted bifacial n-PERT cell process and adopted a design with twelve busbars. The current cells also have a screenprinted 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 a boron diffusion.”

A batch of 12 new M2-sized cells (244.3cm²) measured at ISFH CalTec showed an average conversion efficiency of 23.0%, with the best cell topping 23.2%, and our own 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%. 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 a lower sensitivity to metal impurities, and the absence of light induced degradation (LID). Therefore, n-type PERT technology could become a cost-effective contender to p-type PERC cells. To enable this, the current cells have a screenprinted 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%, coupled to a bifaciality above 90%.

Jia Chen, R&D director at Jolywood, added: “Jolywood targets to bring the best solar solution to the market. 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 technology know-how, we are confident that our bifacial n-type solar cells will achieve an efficiency above 24% very soon.”