Industrial-scale deposition of nanocrystalline silicon oxide for 26.4%-efficient silicon heterojunction solar cells with copper electrodes

To unlock the full performance potential of silicon heterojunction solar cells requires reductions of parasitic absorption and shadowing losses. Yet the translation of the hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H) window layer and copper-plated electrodes to a cost-effective and scalable production-relevant context remains one of the largest roadblocks towards mainstream adoption of silicon heterojunction technology. Here we address the first challenge by developing an industrial-scale high-frequency plasma-enhanced chemical vapour deposition system with a minimized standing wave effect, enabling the deposition of doped nc-SiO_x:H with excellent electron selectivity, low parasitic absorption and high uniformity. Next, we demonstrate seed-free copper plating, resulting in grids with a high aspect ratio and low metal fraction. By implementing the doped nc-SiO_x:H window layer, certified efficiencies of 25.98% and 26.41% are obtained for M6-size bifacial silicon heterojunction devices with screen-printed silver electrodes and copper-plated electrodes, respectively. These results underline the performance potential of silicon heterojunction technology and lower the threshold towards their mass manufacturing.