Screen printable doped self-aligned metallization for solar cells

Alloyed metal contacts to <100> and <111> p-type silicon (Si) were investigated using doped self-aligning metallization techniques [1]. The contact allows the formation of a pn-junction and provides metallization for photovoltaic applications via thick film technology [2]. A formulated screen-printable thick film was annealed above Ag/Si eutectic temperature of 830degreesC. The annealing process resulted in a junction depth of 0.3-1.2 mum and improved adhesion by the reduction of native oxide layer through use of a wetting agent. The technique inhibits shunts (high conductivity paths through the solar cell pn-junction caused by excessive metallization penetration). The technique also reduces the interfacial resistance due to dissimilar materials in contact - a parasitic resistance that also limit solar cell performance. The use of metallic Mg as a wetting agent additive in the thick film silver matrix was explored. Studies were carried out on screen printable thick films and the reducing effects of Mg were investigated using both air and reducing atmosphere (H-2) annealing furnaces. We observed a correlation between increased alloying with reduced series resistance.