Microscopic origin of the aluminium assisted spiking effects in n-type silicon solar cells

Abstract

Contact formation with silver (Ag) thick film pastes on boron emitters of n-type crystalline silicon (Si) solar cells is a nontrivial technological task. Low contact resistances are up to present only achieved with the addition of aluminium (Al) to the paste. During contact formation, Al assisted spiking from the paste into the silicon emitter and bulk occurs, thus leading to a low contact resistance but also to a deterioration of other cell parameters. Both effects are coupled and can be adjusted by choosing proper Al contents of the paste and temperatures for contact formation. In this work the microscopic electric properties of single spikes are presented. These microscopic results, i.e. alterations of the local emitter doping density, the pronounced local recombination activity at the interface between spikes and Si and its influence on the charge collection efficiency, are used to explain the observed dependencies of global cell parameters on the Al content of contact pastes

Study of Low Voltage Prebreakdown Sites in Multicrystalline Si Based Cells by the LBIC, EL, and EDS Methods

“…EDS mapping reveals the enhanced aluminum and oxygen concentrations at these sites (Figures 4 and 6) that well correlate with the results obtained in [2,7], where it was concluded that these breakdowns arise due to contamination of the wafer with aluminium particles before and during processing. It should be noted that, as shown in [16], Al spikes indeed can be formed and in n-Si they can produce short circuits in solar cells. Here, p-Si is used; therefore, Al exhibiting precipitate behavior can be different from that in [16].…”

“…It should be noted that, as shown in [16], Al spikes indeed can be formed and in n-Si they can produce short circuits in solar cells. Here, p-Si is used; therefore, Al exhibiting precipitate behavior can be different from that in [16]. Nevertheless, the results presented confirm the effect of Al containing precipitates on the low voltage solar cell breakdown in accordance with [7].…”

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

“…It has been shown that adding Al powders to Ag pastes for n-type cells can help lower the contact resistivity, but also leads to higher surface recombination and increased line resistivity of the Ag electrode patterns. [5][6][7][8] There has been great interest in potential mechanisms by which the addition of Al reduces the contact resistivity. Previous studies have shown that Al most likely catalyzes the formation of microscale spikes on boron-doped Si emitters, though the composition of these spikes and their mechanism of formation are still debated.…”

“…Previous studies have shown that Al most likely catalyzes the formation of microscale spikes on boron-doped Si emitters, though the composition of these spikes and their mechanism of formation are still debated. [9][10][11] The differing results are possibly due to the variety of frit oxide powders added to the pastes. The frits etch the silicon nitride (SiN x ) at high firing temperatures and form a non-homogeneous interfacial glass layer that creates a complex microstructure at the interface between the Ag contact and the Si emitters.…”

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

“…The contacts feature deeper metal spikes that can be deep enough to penetrate the emitter. The influence of these spikes on cell performance was investigated by different groups [12]- [14] and is a topic of ongoing research activities. The investigation of the contact formation process and the mechanism behind the growth of these metals spikes can lead to a further understanding of their impact on cell performance and possibly help to develop pastes that avoid this negative impact.…”