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.

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.

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 article presents a comprehensive study regarding the impact of the Al electrode on the surface passivation of three TiO x ‐based passivating selective contacts: TiO x :Al/LiF x /Al,TiO x /LiF x /Al, and a‐Si/TiO x :Al/LiF x /Al. A deterioration in passivation is recorded after the deposition of the Al electrode at close to room temperature, where the deterioration correlated to the Al thickness. A thin Al (10 nm) electrode resulted in the most severe passivation decline, while samples with a 100 nm Al electrode showed much less passivation deterioration. Furthermore, it is found that a low‐temperature annealing step led to a partial recovery of the passivation, particularly in the case of TiO x :Al/LiF x /Al and a‐Si/TiO x :Al/LiF x /Al contacts. The presented discovery in this article provides crucial insight into the importance of characterization and evaluation of passivating contacts, which is demonstrated here to be highly sensitive to the deposited metal thickness and the interfacial layers, as well as to the post‐deposition annealing.

Thin SiOx interlayers are often formed naturally during the deposition of transition metal oxides on silicon surfaces due to interfacial reaction. The SiOx layer, often only several atomic layers thick, becomes the interface between the Si and deposited metal oxide and can therefore influence the electrical properties and thermal stability of the deposited stack. This work explores the potential benefits of controlling the properties of the SiOx interlayer by the introduction of pregrown high-quality SiOx which also inhibits the formation of low-quality SiOx from the metal-oxide deposition process. This work demonstrates that a high-quality pregrown SiOx can reduce the interfacial reaction and results in a more stoichiometric MoOx with improved surface passivation and thermal stability linked to its lower Dit. Detailed experimental data on carrier selectivity, carrier transport efficiency, annealing stability up to 250 °C, and in-depth material analysis are presented.

Surface texturing of a silicon solar cell is critical to provide surface antireflection and light trapping. The common texturing method based on KOH as an etchant with isopropyl alcohol (IPA) as a wetting agent suffers two disadvantages: introducing metal contamination and low repeatability. To circumvent the limitation of the KOH-IPA method, we develop a new texturing regime by substituting TMAH for KOH, and a commercial surfactant RENA monoTEX for IPA. This TMAH-monoTEX method shows advantages of non-metal contamination, high reproducibility, short process time and small random pyramids. IBC solar cells fabricated with the TMAH-monoTEX texture achieved an efficiency of 25% with J(sc) of 42.9 mA/cm(2), V-oc of 719 mV and FF of 81.1%.

This paper reports that current widely used metal electrode aluminum results in dramatic passivation deterioration of some dopant-free passivated contacts (DFPC) (e.g. TiOx/LiFx， a-Si/LiFx and a-Si/TiOx/LiFx) after the Al electrode is deposited on the DFPC, which significantly lowers the device performance since excellent surface passivation is one of the key requirements for the successful integration of a full area contact in a solar cell. More interestingly, we find that the Al electrode thickness has a significant impact on the passivation deterioration. A thin Al (10nm) electrode results in the most severe passivation degradation for TiOx/LiFx. The thin TiOx behaves as a sacrifice layer in an a-Si/TiOx/LiFx contact improving the passivation stability upon thermal treatment. The presented result in this study implies that the passivation performance of a passivated contact assessed based on a the widely usage of nanometer-scale metal film on DFPC to mimic a metalized device structure is not fully reliable for evaluating the contact surface passivation quality, and instead a metal layer replicating the final intended device should be implemented, in combination to PL analysis for the extraction of the passivation quality.

Titania (TiOx) is re-emerging to be a passivating material for the surfaces of high-efficiency crystalline silicon solar cells. Numerous sources in the literature suggest that the surface passivation and thermal stability of TiOx deteriorates with increasing film thickness when the TiOx film is thicker than a sufficient thickness. To circumvent this limitation, this study presents a novel process of Al-doped TiOx (TiOx:Al) film, which demonstrates the potential for improved thermal stability and surface passivation. Based on grazing incident X-ray diffraction and UV-Raman measurements, the incorporation of Al impurity in TiOx effectively restrains the crystal phase transformation of the amorphous TiOx layer during deposition. Furthermore, the TiOx:Al films provide better thermal robustness up to 350 °C, which makes it highly compatible with Si solar cell fabrication processes.

Czochralski (Cz)‐grown upgraded metallurgical‐grade (UMG) silicon wafers degrade significantly during high‐temperature processes, eroding their appeal as a low‐cost alternative to conventional electronic‐grade silicon wafers. However, the thermal degradation in UMG wafers can be delayed by utilizing a prefabrication annealing step. Based on this, a high‐efficiency solar‐cell process is modified by selecting a single‐boron diffusion step and applying phosphorus‐doped polycrystalline films as electron‐selective contacts with excellent impurity‐gettering properties to minimize the thermal budget. The application of this modified high‐efficiency solar‐cell process to n‐type UMG‐Cz wafers results in a solar cell with a conversion efficiency of 22.6% on a cell area of 2 × 2 cm2.

Titanium oxide (TiOx) layer is currently re-emerging as a passivating material for high-efficiency crystalline silicon (c-Si) solar cells. For undoped TiOx, it is known that the surface passivation strongly depends on the film thickness and the annealing temperature, as summarized in Table 1 [1] [2]. For example, Gad and Kasemann reported J0s of 40 and 70 fA/cm2 with 1.5 nm ALD TiOx on p-type 1 Ω-cm and 10 Ω-cm wafers, but as the TiOx layer increased to 5.5 nm, the passivation deteriorates significantly with J0s elevated to 680 and 2000 fA/cm2 respectively[3].The loss of surface passivation for thicker TiOx is attributed to a phase transition inside the TiOx during the deposition [1-5].