Screen printing metallization of boron emitters

Abstract

This paper analyzes the influence of the composition of screen printing metal pastes on contacting boron emitters for crystalline silicon solar cells, optimized on the basis of commercial Ag‐paste Ferro 3347 by adding silicon and aluminum. Aluminum provides a lower contact resistance, while silicon prevents the spiking and alloying of aluminum with the silicon of the substrate. The best pastes have turned out to be high Si‐concentrated, which have provided a final specific contact resistance of 3–4 mΩ cm2 on screen printed boron emitters diffused at 1000°C for 8 min, with shunt conductance lower than 0.6 mS/cm2. The final fill factors have been better than 77.5% and open circuit voltages have exceeded 605 mV on Czochralski (Cz) n type 0.7 Ω cm solar cells. These results have proven the feasibility of our screen printing process for p+nn+ structures. Copyright © 2009 John Wiley & Sons, Ltd.

Formation of Ag/Al Screen-Printing Contacts on B Emitters

“…The Ag/Al contact spots grow below the Si surface. Therefore, after cooling down, Si residues can be found between the Ag/Al contact spots and the contact finger for some contact spots (1 Fig. 10] due to the porous structure of the finger.…”

“…This leads to shunting of the p-n junction and deteriorates fill factor FF and open-circuit voltage V oc and thus efficiency of the solar cell [1], [3]. In addition, higher emitter saturation current densities j 0e have been reported for pastes with a high Al content [8].…”

Passivating boron silicate glasses for co-diffused high-efficiency n-type silicon solar cell application

“…4: 30 or 100 nm layer thickness) or the reference stack of Al 2 O 3 /SiN x at firing furnace set peak temperatures of 850-930 C. But, with the increase in firing temperature, the probability of shunting due to damage done to the space charge region using Ag/Al paste increases. 9,14 Since Ag pastes only lead to crystal growth near the surface, this kind of shunting problem does not occur in the same way. For higher temperatures, in contrast to the further decrease of contact resistivity by contact formation using Ag/Al pastes, an increase in contact resistivity occurs for the Ag pastes.…”

“…Until now, it was not possible to reach the same low level of contact resistivity using Ag instead of Ag/Al pastes to contact B emitters with or without established surface passivation layers. 14,15 All presented SiO x :B and SiN x layers are deposited in a single chamber, inductively coupled plasma plasmaenhanced chemical vapor deposition (ICP-PECVD) lab-tool. The lab-tool displays direct as well as remote plasma characteristics for high-density films.…”

Role of aluminum in silver paste contact to boron-doped silicon emitters

“…These features are referred to here as Al-Ag micro-spikes. 19,20 The inset image in Fig. 3 (b) shows the top view of the Si surface after etching away the Ag/Al metals by nitric acid etch Fig.…”