Gallium doping for 24.47% efficient p-type heterojunction solar cells – pv magazine International
The solar industry has been interested in heterojunction technology (HJT) for many years. However, this requires the use of n-type silicon wafers, and wafer producers preferred lower-cost p-type wafers.
This year, HJT again emerges as the best way to improve cell performance. Wafer manufacturers are beginning to produce n-type products on a large scale and are pursuing various cost optimization strategies to close the gap with p-type products.
However, some people in the PV research community choose to pursue the alternative strategy of p-type platelet development for HJT cell production, to match n-type performance. The introduction of gallium doping in the production of pa-type cells has opened many doors for this research, providing a solution to light-induced degradation that does not require high temperatures. There are still a few unanswered questions, but recent research has shown that p-type platelets could be used to make HJT cells that rival n-type performance.
Scientists led by the French research institute CEA INES have demonstrated this potential by manufacturing p-type HJT cells on a pilot line in their laboratory. By using wafers cut from a specially produced ingot with a low level of gallium doping, the group was able to demonstrate an improved efficiency of 24.47%, and results consistently well above 23%.
“This work clearly suggests that the efficiency gap of p-to-n-type SHJ solar cells can be closed without additional costly and/or more complicated process steps,” the group said. “The cells behave similarly to the n-type reference, which looks very promising for field applications.”
The researchers described the cells in “Closing the gap between n- and p-type silicon heterojunction solar cells: 24.47% efficient on lightly doped Ga wafers”, which was recently published in Progress in photovoltaics. Based on previous research, the group worked on the hypothesis that p-type performance must be less than 0.4% of n-type performance to be viable on a cost basis.
The group said further investigation will be needed into the cost of moderate to low level doping for the ingots it purchased specifically for this work. They also note that this time around they made the p-type cells based on the standard process parameters used in n-type production, and that further optimizations of many of them might be possible for close the gap even further.
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