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.

In this work we present a theoretical analysis of charge carriers transport mechanisms in IBC-SHJ solar cells. The concepts of contact and transport selectivity are correlated through the band bending at c-Si interface and are used to identify thin-film silicon parameters affecting fill factor (FF) and open-circuit voltage (V_OC). Additionally, the transport of carriers is associated to energy barriers at the conduction band for electrons and at the valence band for holes. In case of p-type contact, the transport of holes is mainly affected by activation energy and band gap of the p-type layer and work function of the TCO. In case of n-type contact, the activation energy and work function of the doped layer impact the most on transport of electrons. Selective transport is improved by maximizing the collection of majority carrier in each doped contact stack while blocking minority carriers. In particular, low activation energy values of doped layers are crucial to minimize energy barriers for majority carriers and increase the band bending at c-Si interface. Simulation results based on TCAD Sentaurus reveal that the FF increases as the activation energy of the doped layers is reduced. Also, for the p-type contact, the bandgap of p-type layer strongly affects the band bending at c-Si interface. Particularly, widening the bandgap of p-type layer enhances passivation and transport in terms of V_OC and FF but work function mismatch between the p-type layer and the related transparent conductive oxide (TCO) strongly increases as bandgap increases. This possibly makes the device less performant because it is more sensitive to activation energy of the p-layer in combination with the choice of the proper TCO. Considering realistic deposited layers, a wide bandgap p-type layer, in combination with low activation energy, potentially improves hole collection leading to maximal simulated FF = 86.8% and V_OC = 754 mV for a conversion efficiency η = 27.2%.

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.

This paper shows the application of carrier-selective passivating contacts (CSPCs) in c-Si front-back contacted (FBC) and interdigitated back-contacted (IBC) solar cells with different thermal budgets. From lifetime analysis of our poly-Si and a-Si:H CSPCs, three FBC and one IBC architectures are devised to progressively increase efficiency (ç) and achieve record short-circuit current density (JSC): (i) a poly-poly cell (\eta = 19.6%); (ii) a selective emitter structure known as PeRFeCT (Passivated Emitter Rear and Front ConTacts, \eta = 20.0%); (iii) a so-called hybrid solar cell with poly-Si and a-Si:H CSPCs at rear and front, respectively (\eta = 21.0%); and (iv) an IBC solar cell with poly-Si CSPC (\eta = 23.0%, JSC = 42.2 mA/cm2).

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.

Highest conversion efficiency in crystalline silicon (c-Si) solar cells can be enabled by quenching minority carriers' recombination at c-Si/contact interface owing to carrier-selective passivating contacts. With the semi-insulating poly-crystalline silicon (SIPOS, poly-Si) a very good passivation of c-Si surfaces was obtained. We have explored these passivating structures on IBC solar cells and obtained over 22% efficiency with over 23% within reach on the short term. We present in detail the passivation quality of p-type and n-type ion-implanted LPCVD poly-crystalline silicon (poly-Si) and its relation to the doping profile. Optimized poly-Si layers in the role of emitter and BSF showed excellent passivation (J_0,emitter = 11.5 fA/cm² and J_0,BSF = 4.5 fA/cm²) and have been deployed in FSF-based IBC c-Si solar cells using a simple self-aligned patterning process. Applying an optimized passivation of FSF by PECVD a-Si:H/SiNx layer (J_0,FSF = 6.5 fA/cm²) leads to a cell with efficiency of 22.1% (V_OC = 709 mV, J_SC = 40.7 mA/cm², FF = 76.6%). Since over 83% FF has been reached with adjusted metallization technology on similar IBC structures, we believe 23% efficiency is within reach on the short term. Further improvement, especially at J_SC level, is expected by deploying less absorbing carrier-selective passivating contacts based on poly-Si or wide bandgap poly-SiO_x layers (J₀ ~ 10 fA/cm²).

A major limitation in current liquid phase crystallized (LPC) silicon thin-film record solar cells are optical losses caused by their planar glass-silicon interface. In this study, silicon is grown on nanoimprinted periodically as well as on randomly textured glass substrates and successfully implemented into state-of-the-art LPC silicon thin-film solar cell stacks. By systematically varying every layer the whole sample stack is optimized regarding its anti-reflection ability. Compared to an optimized planar reference device, a reduction of reflection losses by -3.5% (absolute) on the random and by -9.4% (absolute) on the periodic texture has been achieved in the wavelength range of interest.