Thin-film silicon single- and multi-junctions are a viable option to manufacture lightweight, flexible solar modules via high-throughput roll-to-roll (R2R) processes, starting from earth-abundant, non-toxic raw materials, at very cost competitive levels and with a range of application spanning from large area solar plants to portable devices. Nevertheless, flexible thin-film silicon modules have currently lower power conversion efficiency (PCE) compared to modules fabricated on glass substrates. Here, we focus on improving the efficiency of flexible single-junction modules by changing the chemical composition and the growth conditions of the p-doped window layer. Highly efficient devices require a window layer with excellent optical and electronic properties so that incoming light photons can easily reach the absorber layer, while photogenerated holes can be promptly extracted from the device. Our baseline modules have a p-doped hydrogenated silicon carbide (p-SiC:H) window layer. In order to simultaneously reduce optical losses and improve the charge collection, we reduced the thickness of p-SiC:H by modifying the plasma enhanced chemical vapor deposition tool, and we inserted a layer of p-doped nanocrystalline silicon oxide (p-nc-SiOx:H) in between p-SiC:H and TCO. The double p-layer modules that we obtained showed a 2% increase in the open circuit voltage compared to the single p-layer modules. Fine-tuning the deposition conditions for both p-layers will further reduce optical and resistive losses and improve the PCE of the modules; additionally, the double p-layer architecture will allow for an accurate control of the light transmission through the window layer, facilitating the current matching for multi-junction modules.