Substitution of silver electrode with an abundant metal — A fundamental study

One of the fundamental bottlenecks for crystalline-Si solar cells to reach a terawatt scale is the scarcity of silver, which is used as the front finger electrode in most commercial Si solar cells today. In this paper, we examine some of the challenges related to low work-function abundant metals, such as aluminum and titanium, as a potential substitution for silver. These challenges include material resistivity, resistance to oxidation, contact resistance and alloying with Si. Valence-mending passivation is proposed as a potential solution to some of the most fundamental challenges including low Schottky barrier to n-type Si for low contact resistance and suppression of aluminum alloying with Si to prevent unintentional p-type doping into n-type Si. Preliminary results are presented on Al and Ti contacts to valence-mended Si(100) surface. Valence-mending passivation allows record-low Schottky barriers of less than 0.1 eV on n-type Si with aluminum and titanium, leading to a 29× reduction in specific contact resistance between titanium and lightly-doped n-type Si. It also suppresses silicidation on Si(100) surface up to ~400°C with titanium as well as nickel.