22.2 % All-Aluminum Screen-Printed Silicon Solar Cells

Abstract

In this work, we present our current development status for all-aluminum screen-printed poly-Si on oxide p-type back junction solar cells. This cell type already features an aluminum front grid which forms locally p⁺-type layers to collect holes. For the rear side metallization, we use special aluminum-silicon (Al-Si) alloy pastes to locally contact the n⁺-type poly-Si after opening the dielectric layer by laser ablation. We compare two different glass frits (A and B) and two different concentrations of silicon in the pastes (low and high). Totally, three pastes are used for rear side metallization: (1) Al-Si paste with low Si and glass frit system A, (2) Al-Si paste with low Si and glass frit system B and (3) Al-Si paste with high Si and glass frit system A. The front and rear side of our solar cells were printed and fired separately. The glass frit system B in paste 2, results in reduced shunt resistance of below 5 kΩ∙cm², negatively influencing the open circuit voltage. The high silicon content in paste 3 prevents local shunting in the cells, consequently reducing the series resistance and leading to a fill factor gain of more than 3 %_abs compared to the other pastes. Our best Ag-free solar cell shows a power conversion efficiency of 22.2 % with an open circuit voltage of 718 mV and was printed using the high-Si amount paste. In a simulation-based synergistic efficiency gain analysis, we identify the rear side recombination at the contacts and the front grid shading as the two dominant factors.