High-productive aluminum deposition of back contacts for hetero-junction solar cells by electron beam evaporation

Currently back contacts of Silicon HJT (Hetero Junction Technology) cells are sputtered or screen printed Ag-layers or structures. The present work aims to replace these cost-intensive manufacturing steps by electron beam evaporation of aluminum using axial beam guns. Al-layers of the necessary thickness have been evaporated with a dynamic deposition rate of up to 3000 nm.m/min while keeping the solar cell below 200°C to avoid any thermal damage of underlying layers and junctions. The deposited aluminum layers exhibit specific electrical resistance of 2.8.10-6 O.cm, specific electrical contact resistance of 10-3 O.cm2 and more than 92 % averaged reflection in the NIR. By exchanging only the metallization step in a standard HJT cell processing without further process-optimization lead to cell efficiencies of 20.6 %.It can be stated that the electron beam evaporation can meet the technical and economical demands of the HJT production process. The high deposition rate can ensure the rear-side metallization of a 100 MW production line in one single deposition equipment.