Low Temperature Laser Metallization for Silicon Solar Cells

Laser transferred contacts (LTC) feature low temperature contact formation, in addition to finger widths w < 30 μm. The LTC process uses the laser induced forward transfer to deposit the contact metal on the solar cell. Here, a laser heats a thin metal layer through an optically transparent support. Modeling of the temperature distribution in themetal and the transparent glass support during laser heating illustrates that evaporating glass at the metal/glass interface propels the metal to the solar cell surface. The electrical contact to the solar cell emitter is directly formed during the transfer process through the anti-reflection coating of the solar cell. Since the laser transfer is not limited to a special material, a variety of contact metals can be used. Our LTCs are based on “clean” materials without heavy metals, like cadmium or lead. First solar cells with nickel/copper metallization result in a cell efficiency η = 17.4% and a fill factor FF = 77.7%.