Reduced Temperature Silver Paste with Low Contact Resistance for Advanced Solar Cell Applications

The electrical contact formation on a crystalline silicon (c-Si) solar cell is generally a well-known phenomenon in the PV industry. The glass component along with inorganic additives in the silver paste are responsible for the reactions with silicon nitride ARC, silicon and silver that may lead to a low contact resistance in a screen printed solar cell. However, the detailed chemistry that controls the thermodynamic and kinetic temperature dependence of these reactions remains widely unknown. Currently, the vast majority of industrial c-Si solar cells are fired at relatively high temperatures (760-810 °C). In this work, it will be demonstrated how an additive, hereby referred to as the activator, can be used in order to reduce the required temperature for forming a low resistance electrical contact by greater than 150°C. Both the formation and nature of silver crystallites and colloids formed on the silicon emitter region and in the glass layer are greatly affected by the activator additive; which is referred to as such due to its ability to abruptly alter the temperature of contact formation in a non-linear fashion. This will create an entirely new temperature range in which a good front grid contact can be formed. This has important implications on current and future cell processing technologies such as PERC, which shows many advantages versus traditional aluminum back surface field (Al-BSF) cells, easily shown by PERC's large gains in internal quantum efficiency (IQE) over a wide range of wavelengths [1,2].