We present large-area "moly-poly" cells, with a front side MoO_x/a-Si:H(i) passivating contact and a rear-side poly-Si/SiO_x stack, and we have demonstrated that MoO_x based c-Si solar cell technology can be scaled to industrial wafer size. Excellent surface passivation was achieved using MoO_x and poly-Si, leading to implied V_oc values above 700 mV, and a final cell V_oc of 687 mV. However, some care needs to be taken to avoid parasitic optical losses in the infra-red (IR) spectral range due to free-carrier absorption (FCA). These losses were investigated by comparing poly-Si layers of different thicknesses, deposited by low-pressure or plasma-enhanced chemical vapor deposition (LPCVD or PECVD), at the rear side of moly-poly cells. We found that ultra-thin PECVD layers are most suitable for solar cell applications due to a very good trade-off between surface passivation and reduced FCA. Based on this result, a 18.1% efficient 9.2 × 9.2 cm² moly-poly cell was made, which is the highest reported efficiency so far for moly-poly cells. Finally, we present a preliminary study of the parasitic IR losses in the MoO_x layer itself, when deposited on either a-Si:H or SiO_x passivation layers.

Electron beam (E-beam) deposited molybdenum oxide (MoO_x) has been investigated for its potential to replace p-type hydrogenated amorphous silicon (a-Si:H) in Si heterojunction (SHJ) solar cells. Excellent passivation was achieved for our best MoO_x/c-Si junction based device, reaching an average implied V_oc (iV_oc) of 734 mV on textured, commercially available 6-inch Cz wafers. This confirms the compatibility of MoO_x as a hole selective layer with industrial SHJ cell processing. A hole barrier was, however, observed for our MoO_x-based solar cells due to inefficient hole extraction. The formation of this hole barrier can be related to annealing of MoO_x and the presence of a native oxide grown on the intrinsic a-Si:H interface layer below. Pre-annealing, followed by an HF treatment on the a-Si:H(i) layer prior to MoO_x deposition, proved to be useful to mitigate the formed barrier, while making it more stable under standard SHJ annealing conditions.