The poly-Si carrier-selective passivating contacts (CSPCs) parasitically absorb a substantial amount of light, especially in the form of free carrier absorption. To minimize these losses, we developed CSPCs based on oxygen-alloyed poly-Si (poly-SiO_x) and deployed them in c-Si solar cells. Transmission electron microscopy analysis indicates the presence of nanometer-scale silicon crystals within such poly-SiO_x layers. By varying the O content during material deposition, we can manipulate the crystallinity of the poly-SiO_x material and its absorption coefficient. Also, depending on the O content, the bandgap of the poly-SiO_x material can be widened, making it transparent for longer wavelength light. Thus, we optimized the O alloying, doping, annealing, and hydrogenation conditions. As a result, an extremely high passivation quality for both n-type poly-SiO_x (J₀ = 3.0 fA/cm² and iVoc = 740 mV) and p-type poly-SiO_x (J₀ = 17.0 fA/cm² and iVoc = 700 mV) is obtained. A fill factor of 83.5% is measured in front/back-contacted solar cells with both polarities made up of poly-SiO_x. This indicates that the carrier transport through the junction between poly-SiO_x and c-Si is sufficiently efficient. To demonstrate the merit of poly-SiOx layers' high transparency at long wavelengths, they are deployed at the back side of interdigitated back-contacted (IBC) solar cells. A preliminary cell efficiency of 19.7% is obtained with much room for further improvement. Compared to an IBC solar cell with poly-Si CSPCs, a higher internal quantum efficiency at long wavelengths is observed for the IBC solar cell with poly-SiO_x CSPCs, thus demonstrating the potential of poly-SiO_x in enabling higher J_SC.

In this work, we present the application of poly-Si carrier-selective passivating contacts (CSPCs) as both polarities in interdigitated back-contacted (IBC) solar cell architectures. We compared two approaches to form a gap between the back-surface field (BSF) and emitter fingers. It is proved that the gaps prepared by both approaches are efficient in preventing carriers’ recombination. To minimize the reflection losses, we developed a novel modulated surface texturing (MST) structure as anti-reflection coating (ARC). It is obtained by superposing a nano-textured SiO₂ layer on the conventional micro-textured pyramids, which are passivated with a-Si:H / SiN_x:H layers. This approach decouples the light harvesting from the Si surface passivation, which potentially results in the highest possible optical and electrical performances of the solar cells. The reflectance (R) of the MST-ARC is very close to that of the high-aspect ratio nano-structured silicon (black-Silicon), achieving R < 1% between 450 and 1000 nm. The J₀ of MST-ARC passivated Si surface (6.3 fA/cm²) is the same as that of standard a-Si:H/SiN_x:H layers passivated pyramidally-textured Si surface. By applying this novel MST-ARC in our IBC solar cell, the highest J_SC observed in a device is 42.2 mA/cm² with a V_OC as high as 701 mV. A spectral response enhancement in case of the MST-ARC cell is observed over the whole wavelength range with respect to the cell with standard SiN_x:H ARC. The highest efficiency achieved in this work is 23.0%, with the potential to reach 24.0% in short term by using more conductive metal fingers.