Structural Investigation of Printed Ag/Al Contacts on Silicon and Numerical Modeling of Their Contact Recombination

摘要

Ag/Al pastes allow for a sufficiently low contact resistivity of less than 5 mΩ cm2 with boron-doped p+ emitters. A drawback of those pastes is an enlarged recombination at the silicon/metal interface below those contacts, compared with Ag pastes. For previous Ag/Al pastes from 2013, the observed recombination is even higher than theoretically expected for a fully metal-covered surface. Newly developed Ag/Al pastes allow for a significant reduction of the recombination below the contact, compared with a 2013 Ag/Al paste; for example, the J0e,m et of an 92Ω/sq. p+ emitter has decreased from 3420 down to 1014 fA/cm2 due to the newly developed paste. For an Rsheet of 137 Ω/sq, the J0e,met is 1399 fA/cm2. Structural investigations of those contacts reveal the microscopic appearance of the contacted region. There are contact spikes of metal grown into the silicon. Those spikes cover 1-1.2% of the entire printed finger area. With values for area fraction and depth of the spikes, we conduct simulations of J0e,m et. With these simulations, we are able to explain the enlarged recombination at the contact interface and describe the experimentally measured J0e,m et for both Ag/Al pastes described in this paper.