Recharged Czochralski (RCz) silicon is now the dominant substrate for industrial photovoltaics, yet research on radial dopant uniformity remains limited. In this study, we apply high-resolution steady-state photoluminescence (PL) imaging of the doping concentration, calibrated using eddy-current resistivity measurements, to characterize radial and axial dopant distributions in RCz-grown silicon wafers doped with antimony (Sb), phosphorus (P), and gallium (Ga). Despite their markedly different segregation coefficients, all three dopants exhibit highly uniform radial concentration profiles, with only weak (<10%) reductions in dopant concentration toward the wafer edges. These trends are consistent with the suppression of radial concentration gradients by crystal-crucible counter-rotation in the RCz process. Localized variations observed in the central similar to 30 mm region are attributed to dopant redistribution driven by buoyancy-and Marangoni-driven melt convection. Axially along the length of the ingot, the wafers exhibit dopant distributions that are consistent with the combined effects of dopant segregation and evaporation: Sb-doped wafers show minimal doping variation along the ingot, whereas P-and Ga-doped wafers exhibit increasing doping concentrations toward the ingot tail. Calibrated PL measurements also reveal changes in apparent doping concentration arising from oxygen-related thermal donor (TD) formation and annihilation in Sb-doped samples after thermal treatments. These results demonstrate that RCz growth yields wafers with excellent radial dopant uniformity for the n-and p-type dopants studied here.

ABSTRACT The fabrication of localized doped polycrystalline silicon (poly‐Si) passivating contacts, such as in an interdigitated back contact (IBC) solar cell, is complex and costly. Inkjet printing offers a promising route to simplify this process; however, unintended doping and cross‐doping from the liquid dopant sources remain a significant challenge. This study demonstrates the effectiveness of a spin‐on SiO x capping layer in suppressing unintended doping in unprinted regions and cross‐doping between dopant species, enabling the simultaneous formation of localized n+ and p+ poly‐Si passivating contacts using inkjet printing via a single high‐temperature annealing step. Secondary ion mass spectrometry (SIMS) mapping reveals uniform doping concentrations within the printed lines, approximately 1 × 10 20 cm −3 for phosphorus and 2 × 10 20 cm −3 for boron in the poly‐Si layers with minimal lateral diffusion at the line edges. More importantly, unintended doping is now reduced to below 9 × 10 17 cm −3 , just 0.5% of the source doping concentrations. Additionally, cross‐doping in the printed region of opposite polarity remains below 5 × 10 18 cm −3 , which is less than 2.6% of the intended doping. These results pave the way for the potential adoption of inkjet printing in simplifying the fabrication of solar cells and other electronic devices.

The fabrication of localized doped polycrystalline silicon (poly-Si) passivating contacts, such as in an interdigitated back contact (IBC) solar cell, is complex and costly. Inkjet printing offers a promising route to simplify this process; however, unintended doping and cross-doping from the liquid dopant sources remain a significant challenge. This study demonstrates the effectiveness of a spin-on SiOx capping layer in suppressing unintended doping in unprinted regions and cross-doping between dopant species, enabling the simultaneous formation of localized n+ and p+ poly-Si passivating contacts using inkjet printing via a single high-temperature annealing step. Secondary ion mass spectrometry (SIMS) mapping reveals uniform doping concentrations within the printed lines, approximately 1 & times; 1020 cm-3 for phosphorus and 2 & times; 1020 cm-3 for boron in the poly-Si layers with minimal lateral diffusion at the line edges. More importantly, unintended doping is now reduced to below 9 & times; 1017 cm-3, just 0.5% of the source doping concentrations. Additionally, cross-doping in the printed region of opposite polarity remains below 5 & times; 1018 cm-3, which is less than 2.6% of the intended doping. These results pave the way for the potential adoption of inkjet printing in simplifying the fabrication of solar cells and other electronic devices.

The development of future crystalline silicon (c-Si) solar cell technologies requires innovative surface passivation layers. Sulfides are a somewhat unexplored class of passivation materials, despite previous reports showing that sulfurization of the c-Si surface enhances surface passivation. Herein, we report a novel transparent passivation stack composed of ZnS/Al2O3, sequentially deposited by atomic layer deposition (ALD). This stack exhibits remarkable surface passivation, reaching a recombination current pre-factor J0 as low as 1.0 fA/cm(2) and implied open-circuit voltages iVoc > 730 mV for a wide range of deposition and annealing conditions. Capacitance-voltage measurements reveal an extremely low interface state density of approximate to 1x10(10) cm(-2) eV(-1), on par with state-of-the-art Si-based passivation layers such as SiO2 and a-Si:H, together with a moderate positive fixed charge. A close lattice match between c-Si and ZnS suggests potential epitaxial growth, which could explain the low interface state density and outstanding surface passivation, despite the observation of a polycrystalline bulk structure. These results establish ZnS as an important new material for c-Si surface passivation, with the potential to enable future innovations either as an interlayer for passivating contacts or as a dielectric passivation layer in c-Si solar cells.

The power conversion efficiency (PCE) of conventional tunnel oxide passivating contact (TOPCon) solar cells is fundamentally constrained by front-side recombination losses in both contact and non-contact regions. Here we demonstrate full-size bifacial TOPCon solar cells incorporating patterned front n-type TOPCon fingers and a full-area rear p-type TOPCon emitter, achieving a certified PCE of 26.34%. The devices exhibit excellent damp-heat stability and negligible light-induced degradation and light-and-elevated-temperature-induced degradation. These advances arise from the engineering of the front n-type TOPCon and rear bilayer p-type TOPCon contacts, enabled through controlled polycrystalline silicon crystallinity, dopant concentration, tunnel oxide properties and optimized silver paste formulation. Integrating this high-performance bifacial TOPCon bottom cell with a wide-bandgap perovskite top cell yields monolithic perovskite/TOPCon tandems with a certified PCE of 32.73% and an open-circuit voltage of 1.961 V. This work provides a scalable and industry-compatible pathway to higher-efficiency TOPCon and perovskite/TOPCon tandem photovoltaics.

This study investigates the impact of strong illumination on the effective hydrogen diffusivity in moderately-and heavily-doped n-and p-type crystalline silicon. Using a photoluminescence-based method calibrated by secondary ion mass spectrometry, we measure the effective hydrogen diffusivity in silicon wafers under both dark and illuminated conditions at 400 degrees C. The results show notable increases in the effective diffusivity in heavily-doped n-type and moderately-doped p-type silicon samples under illumination, with both approaching the diffusivity of the moderately-doped n-type sample. In contrast, no significant changes in the effective diffusivity were observed in moderately-doped n-type and heavily-doped p-type silicon under illumination. Simulations of the spatially non-uniform excess carrier profiles generated by the 532-nm laser illumination source, combined with hydrogen charge state modelling, show that the applied illumination can significantly alter the hydrogen charge state fractions in comparison to their thermal equilibrium distributions. Based on the simulation results, we present a qualitative analysis of how the hydrogen charge state may directly modify the energy barrier for hydrogen diffusion, and may also promote or impede the formation of metastable hydrogen complexes, thereby altering the observed effective diffusivity of hydrogen.

Recent progress in inverted perovskite solar cells (iPSCs) highlights the critical role of interface engineering between the charge transport layer and perovskite. Self-assembled monolayers (SAM) on transparent conductive oxide electrodes serve effectively as hole transport layers, though challenges such as energy mismatches and surface inhomogeneities remain. Here, a blended self-assembled monolayer of (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) and (4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl)phosphonic acid (Me-4PACz) is developed, offering improved surface potential uniformity and interfacial energy alignment compared to individual SAMs. Interactions between the SAMs and ionic species are investigated with simulation analysis conducted, revealing the elimination of interfacial energy barriers through precise energy-level tuning. This strategy enables wide-bandgap (1.67 eV) perovskite solar cells with inverted structures with over 24% efficiency, an open-circuit voltage (Voc) of 1.268 V, and a certified fill factor (FF) of 86.8%, leading to a certified efficiency of 23.42%. The approach also enables high-efficiency semi-transparent devices and a mechanically stacked four-terminal perovskite/silicon tandem solar cell reaching 30.97% efficiency.

We investigate antimony (Sb)-doped Czochralski-grown silicon as an alternative n-type substrate for photovoltaic applications, and characterize their axial resistivity distribution, donor properties, and mechanical strength. We find that Sb-doped ingots can achieve a more uniform resistivity distribution along the axial direction compared to P-doped counterparts. Dopant concentration profiles in P-doped ingots can be accurately modelled using the standard Scheil's equation, accounting only for dopant segregation during solidification. In contrast, modelling Sb-doped ingots requires consideration of both dopant segregation and evaporation effects to fit the dopant distribution accurately. Using electron paramagnetic resonance spectroscopy at 9 K, we observe two hyperfine lines in P-doped samples, and six hyperfine lines for Sb121 and eight for Sb123 isotopes, with the number of hyperfine lines governed by the nuclear spins. We further identify two-atom Sb clustering in the Sbdoped wafers, confirmed through simulations of the additional weak electron paramagnetic resonance peaks. Finally, we find that 140 mu m as-cut planar Sb-doped wafers exhibit slightly higher mechanical strength compared to P-doped wafers.

A noble-metal-free Ni-NC@TiO2 core-shell photocatalyst was developed for efficient hydrogen production from ammonia photodecomposition under visible light without the use of sacrificial agents. In this architecture, Ni nanoparticles are anchored on the nitrogen-doped carbon shell through strong Ni-N interfacial coordination. The conductive NC shell promotes the separation and transport of photogenerated charge carriers, while the Ni sites provide favourable centres for NH3 adsorption and dehydrogenation. Under visible-light irradiation, Ni-NC@TiO2 exhibits a hydrogen evolution rate approximately 43 times higher than that of pristine TiO2. Combined experimental characterizations and DFT calculations reveal that the interfacial Ni-N coupling not only accelerates carrier migration, but also modulates the electronic structure of the Ni sites, thereby lowering the reaction barrier for NH3 decomposition. Meanwhile, the catalyst shows excellent durability, maintaining stable activity over 40 h without detectable deactivation.

To enhance the performance of monolithic perovskite/silicon tandem solar cells toward their theoretical limits and enable commercial-scale deployment, it is essential to quantify local power losses and identify their physical origins. In this study, we apply a method to extract the local tandem series resistance (LTRS), a key contributor to the performance degradation of perovskite/silicon tandem devices. The method is based on bias-voltage-dependent photoluminescence (PL) imaging under two different illumination intensities, coupled with the generalized Planck's law. Finite element simulations demonstrate the robustness of the method under a range of realistic conditions, including current mismatch, low shunt resistance, and luminescence coupling effects. When exemplarily applied to a high-efficiency perovskite/silicon tandem device with a power conversion efficiency PCE of 29%, the method reveals that approximately 1.9% absolute efficiency loss can be attributed to resistive effects. We further investigate the influence of the transient behavior of perovskites on LTRS measurements using a metastable device. The results show that, even for unstable samples, reliable estimations of LTRS can be achieved if an appropriate stabilization protocol is employed. These findings establish PL imaging as a powerful diagnostic tool for identifying performance-limiting regions and guiding the design and processing improvements of next-generation tandem photovoltaics.

We study hydrogen diffusion in silicon by annealing wafers with hydrogen-rich aluminum oxide layers on one surface and intrinsic PECVD silicon films acting as a hydrogen capture sink on the other surface. The hydrogen concentration in the silicon film is monitored via spectrally resolved sub-bandgap photoluminescence, calibrated by comparison with time-of-flight secondary ion mass spectrometry measurements. This provides a convenient and rapid method for hydrogen concentration measurements. Modeling the kinetics of the increasing hydrogen concentration in the silicon film as hydrogen diffuses through the wafer allows the effective hydrogen diffusivity to be extracted at annealing temperatures of 300-450 degrees C, a range that is relevant for silicon solar cell technology, but has not often been directly measured. The extracted hydrogen diffusivities in undoped silicon and both moderately and heavily doped n- and p-type silicon are compared with the existing literature reports. The results match very well with the model of Herring et al. for moderately doped n-type and undoped silicon. For heavily doped n-type and p-type silicon with different dopant concentrations, however, we report significantly reduced effective hydrogen diffusivity values. Finally, we present the modeling of hydrogen charge states in differently doped silicon and consider possible explanations for the reduction in effective hydrogen diffusivity.

Ultrawide-bandgap (UWBG) perovskites are essential for monolithic all-perovskite triple-junction solar cells. However, their performance is limited by severe surface wrinkling, halide heterogeneity and large open-circuit voltage deficits originating from high Br–I ratios. Here we develop a surface reconstruction and halide homogenization strategy that simultaneously regulates crystallization and eliminates stress-induced morphological disorder in 2.0-eV bandgap perovskites. Through synergistic solvent and additive engineering, involving solvent-induced surface reconstruction and transient Cl− incorporation from oleylammonium chloride, surface wrinkling is suppressed, and Br/I crystallization is synchronized with promoted homogeneous halide distribution. The resulting UWBG perovskite films show uniform surface potential, suppressed non-radiative recombination, improved carrier mobility and an open-circuit voltage of 1.46 V. Integrating this UWBG subcell with optimized 1.6- and 1.22-eV absorbers yields monolithic all-perovskite triple-junction solar cells with 30.1% power conversion efficiency (certified 29.3%) and robust operational stability, providing a promising route towards >35% efficient all-perovskite multijunction photovoltaics. Ultrawide-bandgap perovskites suffer from heterogeneities during crystallization. Zhang et al. use solvent and additive engineering to smooth the process for 2.0-eV bandgap perovskites, enabling 30.1% efficiency in all-perovskite triple-junction solar cells.

The drive toward higher solar cell efficiencies and a lower levelized cost of electricity is accelerating the research and development of perovskite/silicon tandem solar cells. Silicon heterojunction (SHJ) bottom cells have traditionally dominated perovskite/silicon tandem research due to their high open-circuit voltages (Voc) (>740 mV) and integration flexibility. However, recent advances in conventional tunnel oxide passivated contact (TOPCon) solar cells, including improvements in front-side passivation, doped poly-Si contact optimization, and laser-assisted firing technologies, have significantly narrowed the Voc gap, a trend that is increasingly reflected in the growing number of TOPCon-based tandem studies. In this work, we review the current status of TOPCon-based bottom cells for perovskite/silicon tandem integration, benchmarking them against SHJ-based tandems in terms of efficiency potential, manufacturability, cost, and scalability. Although certified efficiencies of TOPCon-based tandems still lag their SHJ counterparts, preliminary simulations predict that TOPCon-based tandems can achieve comparable power conversion efficiencies with SHJ-based tandems. A techno-economic analysis indicates that TOPCon’s lower fabrication costs may offer critical advantages for mass and sustainable tandem production. Furthermore, we explore recent advances in process adaptations, including textured surface optimization, atomic hydrogenation, the development of transparent conductive oxide (TCO)-free interconnect layers, and bi-poly TOPCon structures, which collectively enhance the industrial feasibility of TOPCon-based tandem architectures. Finally, we identify key challenges, such as parasitic absorption, surface passivation losses on textured surfaces, sputter-induced damage, and dehydrogenation of TOPCon bottom cells.

Scalable fabrication of wide-band-gap perovskite sub-cells under ambient conditions is essential for commercial perovskite/silic on tandem photovoltaics. However, uncontrolled ambient moisture renders crystallization unmanageable and triggers irreversible surface decomposition. To address this, we innovate a wet-film intervention strategy using bifunctional n-butylammonium thiocyanate (nBASCN) to regulate perovskite crystallization and mitigate the adverse impact of moisture. The strategic incorporation of SCN-into wet films enables homogeneous secondary grain growth with enhanced crystallinity and grain size by decoupling the crystallization process from environmental humidity. Optimally tailored nBA+ cations balance hydrophobicity with SCN--assisted crystallization, constructing a self-volatile 2D hydrophobic barrier that effectively suppresses moisture-induced surface degradation without compromising charge transport. As a result, we achieved a remarkable efficiency of 30.71% (certified 30.51%) for perovskite/silicon tandem devices (1.1664 cm2) and 29.09% for large-area tandem devices (16 cm2), representing the highest efficiency of perovskite/silic on tandem solar cells via scalable fabrication in ambient air.

Understanding metallic impurities in silicon is essential for the development of silicon-based devices such as solar cells. Transition metals such as iron and chromium have been recognised as harmful impurities in silicon, particularly in p-type silicon. As the photovoltaic industry shifted from boron to gallium doping in p-type silicon, understanding the recombination behaviour of chromium-gallium (CrGa) pairs becomes crucial. This study assesses the recombination parameters of CrGa pairs in silicon using both injection-dependent lifetime spectroscopy (IDLS) and deep-level transient spectroscopy (DLTS). Customised Czochralski (Cz) silicon ingots with known amounts of intentional Cr contamination during the ingot growth process were used, with wafer resistivities varying across the range of 0.2 Omega cm-8 Omega cm. The presence of Cr in these silicon wafers was first confirmed by monitoring the CrGa pair association and dissociation processes through lifetime-based measurements, which also confirmed the fully paired state of CrGa pairs. The CrGa concentrations in wafers were confirmed by DLTS. Through IDLS and DLTS, the following CrGa defect parameters were extracted: defect energy level Et= EV + 0.47 eV, electron capture cross section 6n = 5.1 x 10-15 cm2 and hole capture cross section 6p = 1.1 x 10-15 cm2.

The presented work on nanometre scale ultra‐thin tunnel oxide passivated contact (UT‐TOPCon) technology presents a promising pathway for enhancing power conversion efficiency in Si solar cells by mitigating parasitic optical losses. The in‐depth optimisation demonstrates record‐low surface recombination currents for a polysilicon layer under 3 nm thick, measuring 0.8 fAcm −2 on planar and 1.3 fAcm −2 on textured surfaces. Low specific contact resistivities between 2.5 and 5 mΩcm 2 were measured on various samples, confirming its excellent carrier transport properties. Furthermore, optical properties were characterised and the opto‐electrical inputs were incorporated into a comprehensive numerical simulation study to evaluate the impact of its application for Si‐perovskite tandem and various single‐junction Si cell architectures. The results indicate significant performance improvements to Si‐perovskite tandem devices, and very high efficiency potential of 26.7% in front and rear UT‐TOPCon designs and up to 27.5% in interdigitated back‐contact UT‐TOPCon structures.

This study examines changes in the thickness of thermally grown ultrathin interfacial oxide layers in doped poly-Si passivating contact structures for high efficiency solar cells. A comparison of interfacial oxide thickness measured by spectroscopic ellipsometry and Transmission Electron Microscopy (TEM) shows that ellipsometry overestimates the oxide thickness by approximately 0.3 nm when compared to TEM. We also investigated changes in the thickness of interfacial oxide layers after each high-temperature step during the formation of doped poly-Si passivating contacts. The TEM studies demonstrate that the interfacial oxide thickness remains largely unchanged after an intrinsic poly-Si layer deposition on top of the oxide, and also after ex-situ dopant diffusion to form n+ and p+ poly-Si contacts. However, employing a pre-annealing step of the intrinsic poly-Si films at 1000 degrees C prior to dopant diffusion, thickens the interfacial oxides by approximately 0.4 nm, and improves the crystallinity of the doped films. Finally, we investigated the impact of oxide thickness and pre-annealing on the surface passivation and contact resistivity, revealing a positive impact of the pre-annealing step in both cases. Increasing the oxide thickness up to 1.5 nm had minimal impact on the surface passivation but led to a significant increase in contact resistivity.

In this work, we investigate the properties of CuxCryOz thin films deposited by atomic layer deposition (ALD) over a wide compositional range. A significant increase in growth rate is observed for intermediate compositions and shown to arise from an enhancement of the CrOx deposition rate on the CuOx surface. In addition to the characteristics of the deposition process, we explore the structural and optoelectronic properties of these films for compositions ranging from copper-free chromium oxide to chromium-free copper oxide, and for various post deposition annealing temperatures (400-800 degrees C). The resulting composition, optical constants, band gap, valence band maximum and work function are determined and used to draw full band diagrams of the binary and ternary oxides. We report for the first time the experimental work function of the spinel phase CuCr2O4 (5.0 +/- 0.2 eV). Finally, the contact resistivity of the films with p-type silicon is examined to assess their potential use as hole-selective contacts for crystalline Si solar cells. The lowest contact resistivity (1.72 ohm cm2) was found for as deposited Cu0.05Cr0.30O0.65.

This work assesses the thermal stability of n-type Epiwafers after a boron diffusion based on the carrier lifetime measurements and photoluminescence images. The Epiwafers show a high bulk quality (iVoc > 735-745 mV) in their initial state after passivation with PECVD SiNx:H films. After a customized thermal budget for boron diffusion, the Epiwafers did not show any significant degradation, suggesting their high thermal stability. In contrast, some n-type Czochralski (nCz) silicon control samples degraded significantly (∆i Voc = -30 mV) due to the formation of ring defects during boron diffusion.

Herein, we fabricate and characterize localized boron- and phosphorus-doped polycrystalline silicon (poly-Si)/SiOx passivating contacts for silicon solar cells by maskless inkjet printing technology with commercially sourced liquid dopant inks. Moreover, we leverage the advantages of inkjet printing to demonstrate the simultaneous formation of localized p+ and n+ poly-Si/SiOx passivating contact lines by a single anneal at 950 °C for 60 min. Optical microscopy images reveal well-defined dopant lines with features down to ∼60 μm. Microphotoluminescence (μPL) mapping confirms the enhanced surface passivation in the locally printed regions compared to the unprinted regions due to doping. In addition, high-resolution dynamic secondary ion mass spectrometry (SIMS) measurements quantify the total dopant concentrations in the lines, and electrochemical capacitance-voltage (ECV) was applied to measure the electrically active dopant concentrations in co-processed pads. The μPL and SIMS maps clearly reflect the line shapes from optical microscopy images, and exhibit sharp line features, irrespective of line widths or dopant species. More importantly, SIMS analysis highlights unintended doping in unprinted regions and cross-doping when both polarities are co-annealed. Introducing a thick spin-on SiOx protective layer in unprinted regions effectively mitigates unintended doping. Comparison of the μPL and SIMS maps suggests that the unintended doping arises from volatile dopant species released into the gas phase, rather than from the lateral diffusion of dopants. The benefits and limitations of the characterization methods are also discussed. These findings provide valuable insights for the further optimization of inkjet printing for localized doping of poly-Si/SiOx passivating contacts, particularly in interdigitated back contact solar cell architectures.