​Currently, thermal diffusion is used to dope the vast majority of photovoltaic cells, regardless of cell technology. However, implementing the doping processes used in this key stage of PV cell manufacturing can be complex. In research conducted under the ISICELL project, whose aim is to simplify industrial-scale cell manufacturing processes, CEA-Liten modified a plasma-immersion ion implantation (PIII) doping technique developed by plasma-immersion machine manufacturer and CEA-Leti partner IBS.

The modified process utilizes ionized phosphorus or boron precursors accelerated by an electrical field and sprayed onto the surface of the silicon wafers. This mono-facial doping technique offers the advantage of simplifying the entire process while allowing the doping profile to be fine-tuned to obtain doped areas with excellent electrical quality. The process is implemented on a tray of 21 wafers, which is compatible with the production throughputs seen in industrial-scale manufacturing environments.

The technology, initially developed by IBS for microelectronics and surface-treatment applications, was adapted by CEA-Liten specifically for PV cell doping on pilot-scale equipment. It is of particular interest for bifacial cell manufacturing and is currently being adapted for new-generation (passivated contact, tandem) cells. Initial tests conducted at France’s national solar energy research institute, INES, were encouraging.