Perovskite-silicon tandem technology has exceeded the single junction theoretical efficiency limit. However, there is still distance to the thermodynamic limit mainly caused by the fill factor. This work presents a methodology to illustrate the mechanisms of FF loss in perovskite-Si monolithic tandem solar cells. Apart from the series resistance related loss characterized by electroluminescence, another loss factor is from the photoshunt, a phenomenon in which the parallel resistance apparently reduces under illumination in perovskite solar cells due to the moderate charge transport layer mobility. In addoition, the two-diode property of the Si cell can also influence the FF of tandem devices. The photoshunt can be hidden when the bottom cell is over illuminated, which explains highly efficient tandem solar cells are usually bottom cell limited. This work outlines strategies that overcoming the photoshunt issue can move the perovskite top cell closer to low FF losses in tandem solar cells.

Zinc oxide thin films are successfully deposited using plasma‐enhanced chemical vapor deposition (PECVD), representing a novel approach for fabricating transparent conductive oxide (TCO) layers. The initial undoped ZnO film exhibits a polycrystalline structure with a pronounced (002) orientation and low optical absorptance. However, the electrical properties of the film are characterized by high resistivity and instability, primarily attributed to its porous morphology. These limitations can be addressed by incorporating aluminum‐doped zinc oxide or indium tin oxide seed layers, resulting in enhanced and more stable electrical performance. To demonstrate its applicability, this study reports the first successful integration of PECVD‐grown ZnO film as a front‐contact layer in silicon heterojunction solar cells. The addition of seed layers boosts the solar cell efficiency by increasing the fill factor through reduced series resistance. Despite the challenges with the initial film quality and the need to further refine the PECVD conditions to optimize the device performance, this study offers valuable insights into the current limitations and future potential of PECVD for TCO development. This lays the foundation for improving the PECVD process to produce high‐quality TCO, potentially establishing it as an alternative deposition method for next‐generation photovoltaic technology.

Hydrogen (H) is essential for the high performance of advanced crystalline silicon (c-Si) solar cells. Recently, H-related ultraviolet-induced degradation (UVID), which can compromise module stability, has attracted increasing attention from the photovoltaic (PV) industry, yet its underlying mechanisms remain incompletely understood. Here, the severity of UVID in silicon heterojunction (SHJ) solar cells is shown to depend strongly on the illuminated-side passivating-contact design, with transparent passivating contacts (TPCs) exhibiting markedly larger losses in open-circuit voltage (V OC), short-circuit current (J SC), and fill factor (FF) than conventional hydrogenated amorphous silicon (a-Si:H)-based SHJ contacts. Combined material characterizations and device analysis support a picture in which the high transparency of TPC shifts UV energy deposition toward the c-Si near-interface region, where UV-driven Si & horbar;H bond dissociation increases interfacial recombination and degrades chemical passivation. In parallel, UV exposure induces a pronounced resistivity increase in the hydrogenated nanocrystalline silicon carbide (nc-SiC:H) contact stack, consistent with local microstructural/electronic disorder and the possible involvement of enhanced sub-bandgap absorption, thereby raising series resistance (R s) and limiting carrier collection. Collectively, these findings link contact optical transparency, H-related bond dynamics, and nc-SiC:H transport degradation to the distinct UVID signatures of SHJ architectures.

Advanced microscopy techniques have been employed to resolve the microstructure of transparent conductive oxide (TCO) contacts in silicon heterojunction solar cells. Aluminum-doped zinc oxide (AZO) stands out as a TCO material because of its low cost, abundance, and good optoelectrical properties. The polycrystalline AZO thin films have yielded promising results in solar cell design. However, understanding the nanostructure of AZO thinfilm materials is vital for enhancing the cell performance by focusing on the formation of large grains and their influence on the charge-carrier mobility of the film. Therefore, we employed high-resolution transmission electron microscopy (HRTEM) and precession-assisted four-dimensional scanning transmission electron microscopy (4D-STEM) with an automated crystal orientation analysis. These techniques can be used to determine the grain sizes of AZO films sputtered on hydrogenated amorphous silicon (a-Si:H) and hydrogenated nanocrystalline silicon (nc-Si:H) layers. Columnar grains in the AZO/a-Si:H film are evident in the grain mapping with diameters greater than 10 nm, whereas in the AZO/nc-Si:H film, the grains begin at diameters less than 10 nm, showing smaller grains near the substrate than at the top of the film. Additionally, the double-layer with indium-thin doped oxide (ITO)/AZO stack started with grain diameters varying from 5 to 90 nm. They exhibit significantly larger and irregular boundaries. Therefore, microstructural characterization showed that larger columnar grains might lead to higher mobility in the AZO layer. This finding indicates that the impact of the ITO seed layer on AZO significantly enhances grain size, improves charge carrier mobility, and overall improves the power conversion efficiency (eta) to be 23.6% comparable to those of AZO on a-Si:H and nc-Si:H.

Ultraviolet (UV)‐induced degradation (UVID) poses a significant challenge for the prospective mass production of silicon heterojunction (SHJ) solar cells, known for their high efficiency. In this study, the magnified impact of UV radiation when employing a silicon carbide (SiC)‐based transparent passivating contact (TPC) on the front side of SHJ solar cells is reported. A reduction in open‐circuit voltage (VOC), short‐circuit current (JSC), and fill factor of 12%, 6%, and 11%, respectively, is observed after UV exposure. Conventional UVID mitigation measures, UV‐blocking encapsulation, are assessed through single‐cell TPC laminates, revealing an unavoidable tradeoff between current loss and UVID. Alternatively, the utilization of ultraviolet‐downshifting (UV‐DS) encapsulants is proposed to convert UV radiation into the visible light spectrum. An optical simulation method, conducted via OPAL2, is presented to evaluate UV‐DS encapsulants for diminishing UVID in SHJ solar cells with different front contacts. A simple methodology is proposed to mimic the optical property of UV‐DS encapsulants. In the simulation results, additional current gains of up to 0.33 mA cm−2 achievable with suitable UV‐DS encapsulants are highlighted. The factors related to the UV‐DS effects are evaluated and the optimization pathway for UV‐DS encapsulants is elucidated.

Transparent passivating contact solar cells using hydrogenated n-type nanocrystalline silicon carbide (nc-SiC:H(n)) utilize a double-layer stack consisting of one passivation-optimized and one conduction-optimized nc-SiC:H(n) layer. This double-layer configuration limits the fill factor (FF) due to the passivating layer's low electrical conductivity. This study enhances this structure by introducing a gradient layer that transitions from passivating-like to conducting-like properties. While replacing the passivating layer alone does not improve performance, when combining it with an ultrathin passivating seed layer, the gradient layer effectively balances voltage and FF trade-offs. This results in higher device voltage and FF. Microstructural analysis shows hydrogen content near the crystalline Si interface similar to the double-layer approach but with increased electrical conductivity earlier in the layer stack. These improvements boost both FF and open-circuit voltage by 0.6% absolute and over 4 mV, respectively.

Crystalline silicon (c-Si) solar cells with hydrogenated nanocrystalline silicon carbide (nc-SiC:H)-based transparent passivating contact (TPC) achieve enhanced short-circuit current density (J(SC)) compared to conventional silicon heterojunction (SHJ) solar cells but suffer from lower open-circuit voltage (V-OC). The V-OC loss is largely due to sputter damage during Sn-doped indium tin oxide window layer deposition. We evaluate thermal annealing for damage mitigation but find limited restoration due to differing thermal tolerances of TPC and SHJ contacts. Instead, a direct heat-assisted intensive light-soaking (LiSo) treatment effectively heals the sputter damage, improving V-OC above 735 mV and achieving a certified efficiency of 24.17% +/- 0.29%. Detailed investigation highlights the synergistic effects of light and heat in the LiSo process. Additionally, a damage-restoration mechanism related to hydrogen motion is discussed.

The origin of sputter damage during transparent conductive oxide deposition is ion bombardment rather than plasma radiation. Ion bombardment increased recombination, whereas plasma radiation reduced recombination.

In various types of organic/inorganic solar cells, optical response enhancement is consistently observed within the external quantum efficiency spectra owing to the improvement in interface passivation and the suppression of carrier recombination. In this study, we focused on crystalline silicon solar cells and systematically investigated the impact of interface recombination on the optical response upon dual-side illumination using numerical simulations. The results shed light on the interesting phenomenon that the surface recombination velocity has a significant impact on the external quantum efficiency, and it changes as the illumination direction changes. Moreover, from a practical perspective, the spectra of external quantum efficiency under dual-side illumination conditions can act as a powerful tool for the quick diagnosis of the passivation quality at the top and bottom interfaces.

AbstractTransparent conducting oxides, like indium tin oxide, enable lateral charge carrier transport in silicon heterojunction solar cells. However, their deposition can damage the passivation quality in the solar cell. This damage during the sputter deposition is a complex issue that has not been fully understood, particularly in various silicon‐based materials like amorphous silicon, polycrystalline silicon, or nanocrystalline silicon carbide. The degradation in passivation quality observed in, for example, amorphous silicon is not only explainable by UV light degradation. This study explores the origin of this degradation based on the example of hydrogenated nanocrystalline silicon carbide by combining simulations with experimental analyses. It delves into potential sources of damage during the sputtering process and determines that neither primary nor secondary effects from plasma luminescence or electron bombardment are likely contributors to the damage. Similarly, the implantation of ions, as well as the creation of vacancies and ionization of lattice atoms, are also considered improbable causes. It is, however, proposed that the transfer of energy to the crystalline silicon interface via phonons can factor into the degradation of the passivation quality. This transfer might be a plausible explanation for the damage observed in the passivation layers during the sputtering process.

An intrinsic hydrogenated amorphous silicon (a‐Si:H(i)) film and a doped silicon film are usually combined in the heterojunction contacts of silicon heterojunction (SHJ) solar cells. In this work, a post‐doping process called catalytic doping (Cat‐doping) on a‐Si:H(i) is performed on the electron selective side of SHJ solar cells, which enables a device architecture that eliminates the additional deposition of the doped silicon layer. Thus, a single phosphorus Cat‐doping layer combines the functions of two other layers by enabling excellent interface passivation and high carrier selectivity. The overall thinner layer on the window side results in higher spectral response at short wavelengths, leading to an improved short‐circuit current density of 40.31 mA cm −2 and an efficiency of 23.65% (certified). The cell efficiency is currently limited by sputter damage from the subsequent transparent conductive oxide fabrication and low carrier activation in the a‐Si:H(i) with Cat‐doping. Numerical device simulations show that the a‐Si:H(i) with Cat‐doping can provide sufficient field effect passivation even at lower active carrier concentrations compared to the as‐deposited doped layer, due to the lower defect density.

Due to its high transparency, silicon carbide can replace amorphous silicon as a front contact material in crystalline silicon solar cells. Herein, first a look at doping in nc‐SiC:H with different deposition techniques is taken. Then, the influence of various deposition conditions for hot wire chemical vapor deposition‐prepared nc‐SiC:H is investigated. Both the electrical conductivity and the optical bandgap increase simultaneously for a multitude of deposition parameters. Combining a high filament temperature of the catalytic filament, a high hydrogen dilution of the precursor gas and an overall low total gas flow, conductivities of 0.38 S cm −1 in combination with an optical bandgap of 3.2 eV can be achieved. In the last section, a closer look into the dependencies of the layer thicknesses of the two different nc‐SiC:H layers applied in solar cells on the cell performance is taken. While the layer with conducting properties only has minor influences on cell properties, a trade‐off between passivation and fill factor is identified for the passivating nc‐SiC:H layer. For thicker layers, the passivating nc‐SiC:H layer achieves a very high implied open‐circuit voltage above 740 mV, but the fill factor starts to degrade due to a very low conductance of the layer.

One limitation to currently applied passivating contacts like hydrogenated amorphous silicon or polycrystalline silicon is the strong absorption of light in the passivating and contacting layers. To increase the amount of light reaching the absorber material of the solar cell, a more transparent material is needed. Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) is highly transparent, as well as highly conductive and has excellent passivating properties, showing very high generated currents in combination with a good fill factor (FF) and high open-circuit voltage (VOC) when applied in a solar cell. This approach is called transparent passivating contact (TPC). However, the FF is still lower as compared to other state-of-the-art approaches. In this work, a closer look on this reduced FF is taken. It is found that there is a direct trade-off between the passivation and the FF depending on the thickness of the SiC layer. In previous works, the SiC layer consists of two SiC layers, whereas the first deposited SiC layer was grown at a soft deposition condition to not harm the SiO passivation layer and therefore referred as the passivating SiC layer and the subsequent SiC layer was more crystalline and conductive and therefore referred as the conducting SiC layer. We found out that an even thinner passivating SiC layer in combination with a SiC layer with continuous transition of its material properties along the growth direction from more passivation SiC layer-like to conduction SiC layer-like, realized by a slow transition of the temperature of the catalytic filament leads to higher iVOCs in combination with an increased FF, leading to solar cell efficiencies exceeding the previous double-layer nc-SiC:H stack and even the amorphous silicon reference cell

Mitigating the adverse effect of transparent conductive oxide (TCO) sputtering on the passivation quality of the heterojunction contact is very critical for achieving high‐efficiency silicon heterojunction (SHJ) solar cells. Herein, n‐type ultra‐thin (5 nm) nanocrystalline silicon (nc‐Si:H) is utilized as a contact layer in rear‐junction SHJ solar cells. It is revealed that the TCO sputtering damage on the contact layer is caused by the ion bombardment during the sputtering process and cannot be fully recovered by low‐temperature annealing. A more severe passivation deterioration is observed for the devices with nc‐Si:H(n) having a higher microstructure factor. This result is explained by an increased ion penetration depth in the porous nc‐Si:H film. By applying denser nc‐Si:H(n) in SHJ solar cells, the front silicon film stack shows more resilience to sputter damage, yielding a remarkable cell performance on the M2‐size wafer with certificated power conversion efficiency ( η ) of 23.87%. The sputter damage on nc‐Si:H by TCO in SHJ solar cells is explored in depth for the first time from the perspective of silicon thin films.

Herein, an optical loss analysis of the recently introduced silicon carbide–based transparent passivating contact (TPC) for silicon heterojunction solar cells is presented, the most dominant losses are identified, and the potential for reducing these losses is discussed. Magnesium fluoride is applied as an antireflective coating to reduce the reflective losses by up to 0.8 mA cm−2. When applying the magnesium fluoride, the passivation quality of the layer stack degrades, but is restored after annealing on a hot plate in ambient air. Afterwards, a road map for TPC solar cells toward an efficiency of 25% is presented and discussed. The largest part in efficiency gain is achieved by reducing the finger width and by increasing the passivation quality. Furthermore, it is shown that TPC solar cells have the potential to achieve short‐circuit current densities above 42 mA cm−2if the finger width is reduced and the front‐side indium tin oxide (ITO) layer can be replaced by an ITO silicon nitride double layer.

A highly transparent passivating contact (TPC) as front contact for crystalline silicon (c-Si) solar cells could in principle combine high conductivity, excellent surface passivation and high optical transparency. However, the simultaneous optimization of these features remains challenging. Here, we present a TPC consisting of a silicon-oxide tunnel layer followed by two layers of hydrogenated nanocrystalline silicon carbide (nc-SiC:H(n)) deposited at different temperatures and a sputtered indium tin oxide (ITO) layer (c-Si(n)/SiO 2 /nc-SiC:H(n)/ITO). While the wide band gap of nc-SiC:H(n) ensures high optical transparency, the double layer design enables good passivation and high conductivity translating into an improved short-circuit current density (40.87 mA cm −2 ), fill factor (80.9%) and efficiency of 23.99 ± 0.29% (certified). Additionally, this contact avoids the need for additional hydrogenation or high-temperature postdeposition annealing steps. We investigate the passivation mechanism and working principle of the TPC and provide a loss analysis based on numerical simulations outlining pathways towards conversion efficiencies of 26%.

A silicon heterojunction solar cell using silicon carbide as front contact is presented, which features the main advantage of high transparency. To enhance this advantage, an optical loss analysis is performed. It is found that reflection losses play an important role for the solar cell, which can easily be reduced by applying an additional MgF2 coating. The deposition of the coating degrades the passivation quality of the contact but can be cured, eventually leading to a certified short circuit current density of 40.9 mA/cm² and efficiency of 23.99%. Afterwards, a roadmap to a theoretical efficiency of 25% is presented.

N‐type microcrystalline silicon carbide (μc‐SiC:H(n)) is a wide bandgap material that is very promising for the use on the front side of crystalline silicon (c‐Si) solar cells. It offers a high optical transparency and a suitable refractive index that reduces parasitic absorption and reflection losses, respectively. In this work, we investigate the potential of hot wire chemical vapor deposition (HWCVD)–grown μc‐SiC:H(n) for c‐Si solar cells with interdigitated back contacts (IBC). We demonstrate outstanding passivation quality of μc‐SiC:H(n) on tunnel oxide (SiO2)–passivated c‐Si with an implied open‐circuit voltage of 742 mV and a saturation current density of 3.6 fA/cm2. This excellent passivation quality is achieved directly after the HWCVD deposition of μc‐SiC:H(n) at 250°C heater temperature without any further treatments like recrystallization or hydrogenation. Additionally, we developed magnesium fluoride (MgF2)/silicon nitride (SiNx:H)/silicon carbide antireflection coatings that reduce optical losses on the front side to only 0.47 mA/cm2 with MgF2/SiNx:H/μc‐SiC:H(n) and 0.62 mA/cm2 with MgF2/μc‐SiC:H(n). Finally, calculations with Sentaurus TCAD simulation using MgF2/μc‐SiC:H(n)/SiO2/c‐Si as front side layer stack in an IBC solar cell reveal a short‐circuit current density of 42.2 mA/cm2, an open‐circuit voltage of 738 mV, a fill factor of 85.2% and a maximum power conversion efficiency of 26.6%.