Working Jolywood, a Chinese manufacturer of n-type bifacial solar cells and modules, imec's n-PERT (Passivated Emitter and Rear Totally diffused) solar cells dreached a certified front-side conversion efficiency of 23.2 percent. Bifcial cells capture light energy on both sides, providing more power from the same area. 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,” said Loic Tous, project leader at imec for the EnergyVille solar power consortium. “The open circuit voltage (Voc) is now above 690mV with fill factors up to 83%, 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. 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 n-PERT technology has a number of inherent advantages over p-type PERC cell technology, including the potential for higher efficiencies because of a lower sensitivity to metal impurities, and the absence of light induced degradation (LID). This means n-type PERT technology could become a cost-effective contender to p-type PERC cells with a screenprinted front grid and rear soldering pads which together amounts to less than 80mg of silver used per cell.