Nanometallic silver inks for metallization of ITO-coated silicon solar cells. Influence of organic components
Printed inks or pastes based on silver nanoparticles are promising alternatives for the metallization of temperature-sensitive silicon solar cells. We show that the sintering of silver nanoparticles strongly depends on the nature of the capping agent used to stabilize the particles during synthesis and in ink formulation. Particles capped by agents containing nitrogen as coordinative anchor group (between agent and silver surface) show poorer sintering under same conditions compared with particles capped by oxygen containing stabilizers. Polymers also hinder sintering more than shorter oligomers. In order to avoid unwanted spreading of the metal ink or paste during printing, the formulation has to be adjusted to the requirements given by the surface. If samples covered by a layer of indium tin oxide are stored in air, the surface energy rapidly decreases, dropping by around 30-50 % within one day. Thus, wettability and the work of adhesion also become poorer. This has to be taken into account by formulating inks for metallization on ITO layers.