| Work Detail |
A Japanese-German research team has manufactured a TOPCon photovoltaic device by replacing common ion implantation techniques with plasma immersion ion implantation (PIII). The resulting device showed almost the same efficiency as TOPCon cells produced with conventional beamline ion implantation systems.
Researchers from the Tokyo Institute of Technology (Japan) and the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany have manufactured a solar cell based on n-type tunnel oxide passivated contact (TOPcon) technology by applying a manufacturing technique known as plasma immersion ion implantation (PIII) or pulsed plasma doping (pulsed PIII).
The latter consists of a surface modification technique that, unlike conventional ion implantation techniques, surrounds the target element with plasma and subjects it to high negative voltage pulses. Its advantage lies in the ability to implant targets with complex three-dimensional geometries, avoiding scanning systems or target manipulators.
In TOPCon photovoltaic cells, ion implantation is used to locally overcompensate an in situ boron-doped TOPCon layer with phosphorus, improving the quality of the cells electrical and surface passivation.
“Ion implantation using the PIII system simplifies equipment design and significantly reduces equipment costs by eliminating the number of mass separation systems, acceleration components, large vacuum pumps, and operational stages required for sweep implantation,” the scientists explained. “In addition, performance can be increased dramatically because the PIII system has large surface area ion extraction electrodes that can be used for large surface implantation.”
They built the cell with a 156 mm × 156 mm Czochralski (CZ) n-type wafer with a thickness of 180 µm. They used two different implantation systems, known as the Beam line system and the PIII system, for ion implantation and deposited a layer of silicon dioxide (SiO2) on both sides using low-pressure chemical vapor deposition (LPCVD). “For boron doping, BF+ ions were used in the beamline implantation system and BF3 plasma in the PIII system,” they explained.
The manufacturing process concludes with a hydrogenation step, which includes the deposition of a 75 nm thick layer of hydrogenated silicon nitride (SiNx:H) on both sides of the cell.
To evaluate the passivation quality of the device, the research group used the quasi-steady state photoconductance (QSSPC) measurement method, which is a standard tool used in silicon-based photovoltaics to perform injection-dependent measurements. the carrier life on silicon wafers.
The analysis showed that both ion implantation systems used in the experiment achieved almost the same quality of surface passivation under optimized conditions, while showing similar short-circuit current and fill factor. However, it also showed that the Beam line system can lead to a higher quality of surface passivation, which the researchers said could probably be due to the non-optimized annealing conditions.
Tested under standard lighting conditions, the cell built using the Beam line system reached a power conversion efficiency of 20.5% and the one built using the PII system reached 20.1%. “These results clearly demonstrate that the PIII system can be applied to the production of tunnel oxide passivated contact solar cells based on n-type wafers,” say the academics, who point out that this system still presents a Fe (iron) contamination problem. ) that must be resolved to bring the proposed technique to commercial production.
The results are presented in the study “ Plasma immersion ion implantation for tunnel oxide passivated contact in silicon solar cells , ” published in Solar Cell Materials and Solar Cells . |
