Research and innovation hub Imec announced at SiliconPV 2019 that its n-PERT (Passivated Emitter and Rear Totally diffused) solar cells developed with Chinese Jolywood have reached a certified front-side conversion efficiency of 23.2 percent.

With cost-efficient processing and a clear path to higher efficiencies, this makes these n-PERT cells a serious contender to p-PERC technology.

"Compared to the previous results imec reported, we have further optimized 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," 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."

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 percent, and Imec's measurements revealed a bifaciality above 80 percent. 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 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 believe that their bifacial n-PERT cells will soon reach efficiencies above 23.5 percent, coupled to a bifaciality above 90 percent.