imec and its Jolywood Achieve 23.2% Efficiency with n-PERT Solar Cells

April 08, 2019 by Scott McMahan

At SiliconPV 2019, imec reported that its n-PERT (Passivated Emitter and Rear Totally diffused) solar cells developed with Jolywood, a leading Chinese producer of n-type bifacial solar cells and modules, have achieved a certified front-side conversion efficiency of 23.2%.  Bifacial solar cells and modules transform direct sunlight and stray light that bounces off surfaces into electricity, making them more efficient overall.

imec says that with cost-efficient processing and a clear path to higher efficiencies, this makes these n-PERT cells a serious contender to outperform passivated emitter rear cell (p-PERC) solar technology.

"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 twelve busbars. The current cells also have a screen-printed front grid and rear soldering pads that use less silver," says 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."

The twelve new cells that are 244.3 cm² each in area had their performance measured at ISFH CalTech. They demonstrated an average front-side conversion efficiency of 23.0 percent, with the best cell topping 23.2 percent, and imec's own measurements revealed a bifaciality above 80 percent.

Moreover, when used under standard front illumination conditions in combination with an additional 0.15 sun rear illumination, imec claims that the cells can achieve an effective conversion efficiency of almost 26%. In addition, ISFH Caltech measured an average reverse current of -0.4A (at -12V) indicating excellent breakdown characteristics.

n-PERT Advantages Over p-Type PERC

The developed n-PERT technology has a number of inherent advantages over p-type PERC cell technology, which are demonstrated in these newest cells. The n-PERT cells do not suffer from light-induced degradation, and they have the potential for higher efficiencies because of their lower sensitivity to metal impurities. Therefore, n-type PERT technology could become a cost-effective potential competitor to p-type PERC cells, according to imec.

To achieve this potential, the current cells utilize a screen-printed front grid and rear soldering pads which together amounts to less than 80mg of silver used per cell.

Performance Improvements Expected Soon

Imec and Jolywood say that they are confident that their bifacial n-PERT cells will soon reach efficiencies above 23.5 percent and a bifaciality above 90 percent.

"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," Jia Chen, R&D director at Jolywood said.

"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," Jia Chen concluded.