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Commercial screen printing process for high efficiency solar cells

Technology News |
By Nick Flaherty

The development with Chinese cell maker Jolywood is part of the EnergyVille project produces a system with an average 21.9 percent front-side efficiency while dramatically reducing the cost.

Based on this process, imec has also demonstrated screen-printed monofacial n-PERT cells with a conversion efficiency up to 22.8 percent. This compares to efficiencies of 24% for crystalline silicon cells and 19 percent for perovskite thin film cells. Tadem perovskite cells have reached nearly 27 percent efficiency.

The new bifacial cells use 40μm printed silver (Ag) fingers on the frontside and printed aluminum (Al) fingers on the rear that make contact with the emitter. By using Al instead of AgAl for the rear contacts, the cost per cell is lowered to one cent per watt (0.01$/Wp). The new technique avoids problems with spiking of AgAl contacts, allowing the emitter design to be improved for higher efficiency. Although the printed Al fingers on the rear side are inherently wider than the frontside fingers, the bifaciality of the cells is 88 percent, which is better than current state-of-the-art bifacial p-PERC cells.

On a batch of M2-sized cells (area: 244.3 cm²), an average conversion efficiency of 21.9 percent was demonstrated, with the best cell topping 22.1 percent. These results were measured using an ISE CalLab calibrated reference cell under standard test conditions using a AAA-class WACOM solar simulator. Used in bifacial operations under standard front illumination conditions in conjunction with an additional 0.15 sun rear illumination, these cells can achieve an effective efficiency of 25 percent.


Imec also built monofacial nPERT cells with efficiencies up to 22.8 percent, where the back of the cell is fully covered with printed Al with dot openings in the dielectric to contact the B-doped 
emitter.

“We are very pleased with the bifacial nPERT results obtained in close collaboration with Jolywood. These results fit very well with our roadmap towards 22.5 percent printed bifacial nPERT cells and 23.5 percent monofacial nPERT cells by the end of 2018,” said Loic Tous, project leader at imec/EnergyVille. “Jolywood is aiming at developing the world’s best n-type cells and modules and we believe we are uniquely placed to help them reach that target.”

“Jolywood always strives to be at the forefront of the n-type industrial technological developments in PV industry. The performance, reliability and bifacial gain of n-type bifacial solar cells can lead to much lower levelized cost of electricity (LCOE) and bring more benefits to our customers,” said Dr Zhifeng Liu, R&D director of Jolywood.

Jolywood is showing these cells at a tradeshow in Shanghai this week.

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