In September 2022, the research project “Selective Polysilicon Finger” (SelFi) started at ISC Konstanz. It is executed together with the project partners Centrotherm, CE Cell Engineering and Fraunhofer CSP and runs over a project period of three years. The research budget for the ISC Konstanz is 1.5 M€.
In SelFi, an industrial manufacturing process for the implementation of local passivated contacts on the cell front side of TOPCon solar cells is to be developed and subsequently also made usable for IBC solar cells. For both cell concepts, the contacts are to be optimized using the LECO process.
TOPCon solar cells have been developed by many research institutes and companies in recent years and are now increasingly being manufactured in industrial production and sold commercially. Voc of just over 700 mV and efficiencies of 23.0-23.8% are achieved. The voltage of such cells is limited mainly by recombination on he front side, so improvement of the cell front side is necessary to achieve further increases in efficiency. To avoid optical losses due to parasitic absorption, structured passivated contacts are necessary.
The addition to the standard TOPCon process flow to be developed is based on local laser doping of poly- Si to produce p+ poly-Si regions that are etch-stable in alkaline solution (patent pending by ISC Konstanz). In this way, local passivated contacts are to be implemented on the front side of the solar cell in order to significantly increase the efficiency of the solar cell, mainly by increasing the cell voltage to 715-720 mV.
Another possible application of the process to produce such local contacts is for IBC solar cells. Here, the local treatment by the laser enables the fabrication of separate p+ doped poly-Si regions. In this way, the ZEBRA cell, which was developed at the ISC Konstanz and is now in industrial mass production, is to be improved to enable further increases in efficiency.
Besides the fabrication of such patterned poly-Si areas, their contacting by means of screen-printed silver pastes represents an important challenge. In particular, the low recombination contact formation of p+ doped poly-Si layers has not yet been solved satisfactorily. Therefore, LECO processes are to be developed in SelFi to enhance the contact formation for both TOPCon and IBC solar cells.
SelFi: Selektive Polysilizium Finger
Funding source: Federal Ministry for Economic Affairs and Climate Action (BMWK)
Funding code: 03EE1138A
Term: 01.09.2022 until 31.08.2025
Budget of the ISC Konstanz: 1.527.913 €
Topic: In SelFi, an industrial manufacturing process for the implementation of local passivated contacts on the cell front side of TOPCon solar cells is to be developed and subsequently also made usable for IBC solar cells. For both cell concepts, the contacts are to be optimized using the LECO process.
Project partners: centrotherm international AG, CE Cell Engineering GmbH, Fraunhofer CSP