| Work Detail |
Scientists at Fraunhofer ISE have tried to use epitaxially grown p-type silicon wafers with TOPCon rear emitter (TOPCore) solar cells with the aim of reducing production costs and carbon footprint.
The Fraunhofer Institute for Solar Energy Systems (ISE) in Germany has proposed the use of epitaxially grown p-type silicon wafers in TOPCon back emitter solar cells (TOPCore), which combine tunnel oxide passivated contact (TOPCon) technology. with a rear emitter instead of a front pn junction.
Epitaxially grown p-type wafers, also called “EpiWafers”, offer a low-cost, low-carbon material for solar cells, providing higher voltages and fill factors compared to cells with a front-face collector-emitter .
Epitaxially grown p-type wafers, also called “EpiWafers”, offer a low-cost, low-carbon material for solar cells, providing higher voltages and fill factors compared to cells with a front collector emitter.
The scientists cultured p-type Cz-Si wafers with a resistivity of 2.5 O cm and a diameter of 150 mm using a chemical vapor deposition (CVD) batch reactor at atmospheric pressure. They then chemically cleaned and passivated the wafers with a surface passivation layer of aluminum oxide (Al2O3) deposited by plasma-assisted atomic layer deposition (ALD) at 180ºC for 78 cycles, resulting in 10 nm layers. thick on both sides.
“The resulting sample set consists of EpiRef wafers with a final thickness of 110 µm and three different base resistivities of 3, 14, and 100 O cm,” they noted.
By applying a front finger grid design to all of the EpiRef wafers, the team observed that each of the three devices could potentially achieve power conversion efficiency greater than 25%. They also observed that the presence of iron (Fe), chromium monoboride (CrB) and boron (BO) defects in EpiWafers did not negatively affect cell performance, demonstrating the high quality and purity of epitaxially grown wafers. .
"In our case, these structural defects, caused by epitaxial growth, can be avoided using another susceptor design," the academics say. “Zones free of structural defects retain their excellent material quality during high-temperature processing.”
They presented the novel fabrication technique in “ Epitaxially Grown p-type Silicon Wafers Ready for Cell Efficiencies Exceeding 25% ,” recently published in RRL Solar .
In April 2021, Fraunhofer ISE claimed to have achieved an efficiency of 26.1% for a TOPCore solar cell.
“Based on a systematic simulation-based analysis, we were able to derive some fundamental design rules for future high-efficiency silicon solar cells above 26% efficiency,” said Stefan Glunz, division director for photovoltaics research at the time. FraunhoferISE. "Solar cells with double-sided contact have the potential to achieve efficiencies of up to 27%, thus surpassing the previous world record for silicon solar cells." |
