Building blocks for back-junction back-contacted cells and modules with ion-implanted poly-Si junctions

Abstract

We propose a process for a back-junction back-contacted solar cell (including module interconnection) combining a high efficiency potential and a lean process flow. This structure offers potential for (i) a high J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> - no optical shading losses due to the absence of front-side metallization and minimized absorption losses at the cell front-side, (ii) a high V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> - excellent passivation including “passivated contacts” based on poly-Si/c-Si junctions, and (iii) a high FF - large area contacts with low contact resistance and the absence of busbar losses due to a two-layer metallization. A lean process flow becomes feasible by utilizing two enabling technologies - in situ patterned ion implantation and module interconnection by laser welding (AMELI). We present experimental results for the main building blocks: (1) Patterned ion implantation yields an excellent recombination behavior homogeneously on 6", (2) Ion-implanted poly-Si / c-Si junctions enabling V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> values up to 742 mV and J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0e</sub> values down to 1.3fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , (3) Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> front-side passivation enabling Jsc values up to 41.8 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and IQE values > 1 for λ <; 350 nm, and (4) busbarless, silver-free AMELI two-layer interconnection. As an intermediate step, we fabricated ion-implanted BJBC cells with conventional junctions and metallization with efficiencies up to 22.1% on 6".