Effect of Pt Additions in the Interconnections on the Resistivity and Power Output of Solar Modules

Intermetallic compound (IMC) layers growth in the interconnections of solar modules is inevitable once the solar modules are in use. Higher temperatures (warmer climates) may accelerate the growth of these compounds, leading to faster degradation of the solar modules. In this paper, the effect of Platinum (Pt) additions on the interfacial reaction, contact resistivity and power output of solar module have been investigated. The changes in IMC morphology was studied using the scanning electron microscope (SEM) with an energy dispersive X-ray (EDX). The contact resistivities of solder joints were measured using the transfer length method. Solar modules with varying amounts of Pt additions were constructed and their power outputs under natural sunlight were compared to the reference solar module constructed with a commercial Sn-3.0Ag-0.5Cu (SAC305) solder. Experimental results showed that minute Pt additions effectively suppressed the IMC growth during isothermal aging at 150°C for up to 500 hours. This was reflected in the reduced contact resistivities ranging between 20->60% when 0.10wt.%-0.50wt.% of Pt were added to the SAC solder. In trend with the reduced resistivities, the solar modules containing Pt recorded higher power outputs and lower degradation rate under natural sunlight exposure. Pt is believed to dissolve and form an ternary compound, (Cu,Pt)6Sn5 which is less susceptible to decompose into the more detrimental Cu3Sn IMC layer, thus slowing down the overall degradation of the solar panels.