Influence of Al Particle Size and Firing Profile on Void Formation in Rear Local Contacts of Silicon Solar Cells

Abstract

Abstract-In this paper, the influence of Al particle size and the applied firing profile on void formation in local rear contacts of wafer-based silicon solar cells is investigated. Samples with a passivated emitter and rear cell (PERC) rear, but without front metallization, were metalized with six different Al screen-printing pastes, i.e., both commercial and homemade, featuring different particle size distributions and fired in a rapid thermal processing furnace with different firing profiles. Voids were detected with scanning acoustic microscopy measurements, and the fraction of voids in rear local contacts was analyzed. It was shown that the heating phase of the firing process has the strongest influence on void formation. With slower heating, void formation could be reduced to a fraction lower than 5% of the local contact area. Furthermore, it was shown that Al pastes consisting of a mixture of small and large Al particle sizes have a positive effect on the formation of voids.

Kirkendall void formation in reverse step graded Si1−xGex/Ge/Si(001) virtual substrates

“…This formation of voids appears to relieve tensile strain by Ge incorporation in SiGe vacancy sites. When the voids start to form in greater density, the strain in the SiGe step layer drops back to 0.2%, as seen at point (6) in the strain plot of figure 14 for a Si Ge 0.46 0.54 step. The strain then starts to increase again as another lower Ge content step layer is grown, possibly due to the voids in the Ge underlayer.…”

“…: Cu/CuSn interfaces) [3] and bonding between metals (e.g. : Au and Al) to semiconductors in integrated circuits [4] and photovoltaic cells [5,6]. Plastic deformation caused by thermal aging and electromigration have been shown to aid nucleation and growth of voids leading to poor electrical conductivity to the contacts.…”

“…Tensile strain relaxation has been employed in reverse linearly graded (RLG) Si Ge Ge Si 001 1 x x -( ) virtual substrates to create strain tuned platforms of 4 10 cm 6 2 -TDD and 3 nm rms roughness (R rms ) [16]. This type of virtual substrate has led to breakthrough high hole mobility in Ge quantum well channels, both at room temperature [17] and 12 K [18] for spintronics applications [19].…”

Effects of Different Particle-Sized Al Powders on Sintering Properties of Aluminum Paste in Crystalline Silicon Solar Cell

“…The formation mechanism of Al-Si contact [15][16][17][18][19] and the influence of Al BSF on cell performance have been thoroughly studied [20][21][22]. However, relevant researches were mostly focused on the changes in cell performance caused by paste [23][24][25]. Each of these phenomena needs to be investigated, particularly how each may be impacted by the parameters of the Al powder.…”

Al‐density variation as one driving force for void formation in PERC solar cells

“…Previous studies concerning void formation dealt e.g. with the impact of contact geometry and contact opening technique, paste composition, firing conditions and post laser treatment . Additionally, an insufficient surface wetting during contact formation process has been discussed as an essential origin of void formation .…”