Formation of fire-through silver metal contacts on the porous silicon surface for silicon solar cells

In the present study, the ohmic and microstructural properties of the fire-through Ag metal contacts formed on planar and thin layers of the porous silicon for the silicon solar cells are investigated. The SEM characterization of the Ag contacts shows that sintering of the contacts at high temperature enables to fire-through the applied Ag paste onto the etched porous silicon surface an results a good ohmic contact between the Ag metal and the n⁺-S surface. It shows that the interaction of the Ag conductor paste with the porous silicon follows a preferential reaction due to the high etch-rate of the molten glass-frit contained in the Ag paste. The specific contact resistance (ρc) of the Ag metal/PS/n+ Si contact structure was estimated using the extrapolation technique based on the three-point probe method. It shows that ρc = = 1.025 × 10⁻⁴ Ω-cm² is obtained for contacts sintered at 825 °C for 90 sec in air ambient while contacts sintered at 750 °C has resulted ρc = 12.0 ×10⁻² Ω-cm2. The ohmic losses of the contact structure were calculated based on the methodology for the relative power loss algorithm that accounts the total ohmic loss associated with the current traveling through various resistive components of the screen-printed solar cell normalized to the unit cell area.