Effect of Ag Particle Size in Thick-Film Ag Paste on the Electrical and Physical Properties of Screen Printed Contacts and Silicon Solar Cells

The impact of the Ag particle (metal powder in the screen printed paste) size on the quality of Ag thick-film ohmic contacts to high-sheet-resistance emitters of Si solar cells is investigated. Spherical particle size wasvaried in the range of 0.10-10 μm (ultrafine to large). Even though ultrathin glass regions are achieved for the large particle paste, giving low specific contact resistance (ρ c ), secondary ion mass spectroscopy measurements showed a higher Ag concentration (>10 1 5 cm - 3 ) at the p-n junction that increased the junction leakage current (J o 2 ) and decreased the V o c by ∼7 mV and fill factor (FF) by ∼0.02. Pastes with ultrafine Ag particles generally produced a thick glass layer at the Ag-Si contact interface, which increased ρ c and series resistance (R s ) (≥ 1 Ω cm 2 ), and lowered the FF by ∼0.03. Small to medium size Ag particles in the paste produced thin glass regions and many regularly distributed Ag crystallites at the contact interface. This resulted in low R s (< 1 Ω cm 2 ), high shunt resistance (60,558 Ω cm 2 ), low J o 2 (∼20 nA/cm 2 ), and high FF (0.781). Cell efficiencies of ∼17.4% were achieved on untextured float zone Si with 100 Ω/□ emitter by rapid firing of screen printed contacts in a lamp-heated belt furnace.