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 explores the impact of various rear contact configurations on the AC impedance characteristics of ptype crystalline silicon (c-Si) solar cells. We fabricated and examined six otherwise identical cell structures with varying rear contact configurations, including direct Ag/c-Si contacts and configurations with MoOx or AlyTiOx/ TiOx/MoOx interlayers, paired with Ag or ITO/Ag electrodes, in p-type c-Si solar cells with front homojunction contacts. The cells exhibited efficiencies ranging from 12.5 % to 22.5 % and were characterized using various electrical techniques, including current-density-voltage (J-V), external quantum efficiency (EQE), capacitance-voltage (C-V), capacitance-frequency (C-f), and impedance spectroscopy (IS) measurements, in order to correlate photovoltaic performance with AC electrical features. We find that the influence of the rear contacts is clearly identifiable in the AC characteristics of the devices. In particular, these techniques uncovered variations in carrier lifetimes, junction behavior, the presence of ohmic or Schottky contacts, as well as allowing the identification of traps and revealing the influence of series resistance in fully metalized cells, all linked to the different rear contact configurations. These findings reveal the ability of AC impedance techniques to distinguish contributions from different regions of the device to overall performance, providing complementary information to conventional DC electrical techniques. As such, AC impedance serves as an important tool for contact development in c-Si solar cells, particularly for novel contact structures such as those utilizing transition metal oxides (TMOs).

ZnO-based electron-selective passivating contacts, with a structure analogous to conventional polysilicon passivating contacts, but offering better optical transparency, have recently emerged as a promising technology for silicon solar cell applications. However, there remain significant disagreements over the optimum ZnO doping level as well as limited information on the connection between film properties and passivating contact performance. In this study, we comprehensively investigate the influence of Al doping ratio in atomic-layer-deposited ZnO:Al films within a SiOx/ZnO:Al/Al2O3 stack, where the Zn:Al cycle ratio was adjusted between 60:1 to 2:1 using a supercycle approach. The effect of Zn:Al cycle ratio on passivation and contact performance is correlated with the structural, electrical and optical characteristics of the resulting films. For thicker films, we observe a reduction of passivation with increasing Al doping, which can be alleviated by increasing the number of initial ZnO cycles before Al doping is introduced. In contrast, doping improves passivation of thinner films and also increases the effectiveness of hydrogenation by thicker Al2O3 capping layers. X-ray diffraction spectra reveal a transition in the preferred crystallographic orientation from (002) to (100) upon the incorporation of Al2O3 capping and doping. Increasing doping also leads to a significant blueshift of optical absorption. The minimum contact resistivity is obtained at a 15:1 cycle ratio (3.64 eV band gap), coinciding with the maximum electron concentration and minimum work function. The optimised stacks combine an implied open-circuit voltage of 725 mV (300 & micro;m wafer) with a contact resistivity of similar to 70 m Omega cm2. Our results help to reconcile apparent disagreements in the findings of previous studies.

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.

Over the past decade, silicon solar cells with carrier-selective passivating contacts based on polysilicon capping an ultra-thin silicon oxide (commonly known as TOPCon or POLO) have demonstrated promising efficiency potentials and are regarded as an evolutionary upgrade to the PERC (passivated emitter and rear contact) cells in manufacturing. The polysilicon-based passivating contacts also exhibit excellent gettering effects that relax the wafer and cleanroom requirements to some extent. In this work, we experimentally explore the impact of bulk iron contamination and polysilicon gettering on the passivation quality of the polysilicon/oxide structure and the resulting solar cells performance. Results show that both n- and p-type polysilicon/oxide passivating contacts are not affected by iron gettering, demonstrating robust and stable passivation quality. However, for a very high bulk iron contamination (1 x 1013 cm-3), the accumulated iron in the p-type lightly boron-doped emitter in crystalline silicon would degrade the emitter saturation current density. This can cause a reduction in both open-circuit voltage and short-circuit current. Meanwhile, this very high iron content (1 x 1013 cm-3) can further degrade the fill factor and temperature coefficient of the cells. On the other hand, for an initial iron content of 2 x 1012 cm-3, which should be well above the iron level in the current industrial Czochralski silicon wafers, the resulting cells demonstrate similar performance as the control group with no intentional iron contamination. This work brings attention to both the benefits of polysilicon gettering effects as well as the potential degradation due to the accumulation of metal impurities in the p-type emitter region.

This study reports on the electronic properties of industrial phosphorus-doped n-type silicon ingots for photovoltaic applications grown using the Recharged Czochralski method. The electronic quality is assessed via carrier lifetime measurements, both directly on the ingots and on passivated wafers, and via implied open-circuit (iVOC), and implied maximum power point (iV(MPP)) voltages. The wafers are studied in the as-grown state, and after various high temperature steps, including Tabula Rasa, phosphorus diffusion gettering, and boron diffusion. The material exhibited very high bulk quality, with bulk lifetimes up to 8 ms at an injection level of 5 x 10(14) cm(-3), and with iVOC (1-sun) values up to 750 mV, prior to any high temperature processing. A Tabula Rasa step did not significantly improve the wafer quality, indicating a low presence of oxygen-related defects in this material, consistent with the low interstitial oxygen content of below 5 x 10(17) cm(-3). However, phosphorus diffusion gettering improved the wafer quality, especially towards the tail end of each ingot, and at lower injection levels near maximum power point. Phosphorus diffusion gettering increased the iV(OC) (1-sun) of the wafers by around 5 mV, approaching the Auger limit. Additionally, a boron diffusion step had minimal impact on the bulk lifetimes. Overall, our findings suggest that these RCz-grown n-type wafers exhibit very high quality, approaching the Auger limit near open-circuit, and are well-suited for high-efficiency solar cells without the need for additional high-temperature processing.

The need to increase transparency in existing passivating contacts for crystalline silicon solar cells has motivated the development of transparent contacts based on transition metal oxides (TMOs). Among hole‐selective materials, molybdenum oxide (MoO x ) has achieved the greatest success so far. However, despite providing low contact resistivity, MoO x relies on an intrinsic hydrogenated amorphous silicon (a‐Si:H(i)) interlayer to achieve high levels of surface passivation and thus high open‐circuit voltage at a device level, partially defeating the objective of improved transparency. Herein, we report unprecedented performance for a‐Si:H‐free MoO x ‐based contacts by employing an alternative passivating interlayer based on a well‐engineered chlorine‐containing Al‐alloyed titanium oxide/titanium dioxide (Al y TiO x /TiO 2 )stack. The resulting Al y TiO x /TiO 2 /MoO x stack achieved record levels of passivation, reaching J 0 values as low as 16 fA cm −2 , closer to values reported for a‐Si:H‐based contacts, while maintaining lower contact resistivity, well below 100 mΩ cm −2 . Additionally, the stack presents improved transparency compared to a‐Si:H‐based contacts, with gains in short‐circuit current density of at least 0.8 mA cm −2 . The work pushes the performance of hole‐selective passivating contacts based on TMOs to new levels, enabling a record efficiency of 22.53% for cells with fully transparent hole‐selective passivating contacts. This work serves as an important stepping stone toward low‐thermal‐budget, simple manufacturing of high‐efficiency solar cells.

Passivating contacts based on transition metal oxides are of great interest for applications in crystalline silicon (c‐Si) solar cells due to their improved optical transparency and potential cost reduction. In this work, the contact resistivity and passivation for thermally evaporated Cu 2 O are investigated and optimized, with and without an Al 2 O 3 interlayer, as a hole‐selective contact to c‐Si. Additionally, we implement an Al y TiO x /TiO 2 stack as a novel passivating tunnel interlayer for hole‐selective contacts, achieving an implied open‐circuit voltage iV oc of 630 mV and a record‐low J 0 of 212 fA cm −2 while maintaining a contact resistivity ρ c of 62 mΩ cm 2 . A record‐low ρ c of 8 mΩ cm 2 for Cu 2 O‐based contacts is also demonstrated at the expense of passivation. The addition of the interlayer resulted in a 2% absolute improvement in the efficiency of proof‐of‐concept c‐Si cells with full‐area rear Cu 2 O contacts, reaching 19.1%.The demonstration of this novel interlayer stack provides new avenues to improve the performance also of other hole‐selective passivating contacts.

The passivating contacts based on polysilicon/oxide (commonly known as TOPCon) has emerged as the next generation high-efficiency silicon solar cell technology. Besides its excellent passivation and carrier selectivity, polysilicon/oxide structure also exhibits strong impurity gettering effects. However, it is not entirely clear how bulk iron contamination and subsequent gettering would affect the polysilicon/oxide based solar cells. In this work, we experimentally compared and assessed the impact of iron gettering on the polysilicon/oxide passivation quality and firing stability. Subsequently, polysilicon/oxide cells with different initial bulk iron concentrations were fabricated and analyzed. Results show that the polysilicon/oxide structure is unaffected by iron gettering, while the boron doped emitter degrades due to the accumulation of iron (i.e. gettering). Together with the remaining bulk Fe contamination (if gettering is insufficient for a high iron content), the degraded boron doped emitter can degrade both the open-circuit voltage and short-circuit current. Meanwhile, an increased ideality factor is observed with increasing initial bulk iron concentrations, exhibiting a reduced fill factor. In addition, the cells with a higher iron contamination is found to be more temperature sensitive.

We demonstrate the beneficial effect of a pre-annealing step prior to the boron diffusion on passivation and contact resistivity of industrially LPCVD deposited poly-Si/SiOX hole-selective contacts. We investigate the influence of the pre-annealing temperature on passivation quality, measured as implied open-circuit voltage and recombination current density, and on changes in crystallinity, characterized by Raman spectroscopy. A clear increase in passivation quality is observed on planar and textured surfaces as well as for various poly-Si thicknesses (100-230 nm) and thermal SiOX growth temperatures (600-800 degrees C). On planar surfaces and without the use of atomic hydrogenation, we report an increase in iVOC of around 5 mV with every additional increase of pre-annealing temperature by 50 degrees C (>900 degrees C) leading to an iVOC of 720 mV (J0 = 9.3 fA/cm2). After atomic hydrogenation, the effect of the pre-annealing is less pronounced. Nevertheless a gain in iVOC (reduction in J0) of 5-10 mV (2-5 fA/cm2) is achieved when comparing samples without pre-annealing with samples after a pre-annealing at 1050 degrees C. On textured surfaces on the other hand, this trend is more pronounced after atomic hydrogenation, for which a pre-crystallisation at 1050 degrees C leads to an iVOC (J0) of 705 mV (16.8 fA/cm2), which is a gain (reduction) of 24 mV (21.7 fA/cm2) compared to samples without a pre-annealing step.

Herein, high-quality localized phosphorus-doped polycrystal-line silicon (poly-Si) passivating contacts containing nanoscale poly-Si film (similar to 100 nm) on an ultrathin SiOx layer (similar to 1.5 nm) were fabricated via an inkjet printing technique. A detailed study of the impacts of inkjet printer settings, dopant concentration, and annealing temperature on the poly-Si passivating contact performance (represented by implied open-circuit voltage iVoc and contact resistivity rho c) was carried out. By applying optimized process conditions on symmetrical industrially processed intrinsic poly-Si/SiOx/n-type crystalline Si (c-Si) substrates, good surface passivation was achieved with an iVoc of 699 mV, together with a low rho c of 6.4 m omega center dot cm2, after annealing at 975 degrees C. After a hydrogenation treatment via the deposition of aluminum oxide (AlOx)/silicon nitride (SiNy) stack and subsequent forming gas annealing (FGA), the optimum annealing temperature shifted to 950 degrees C and the iVoc was further improved to an excellent value of 729 mV. Optical images reveal that a line width of 75 mu m can be realized on a mechanically polished silicon wafer. Moreover, high-resolution micro-photoluminescence (mu-PL) maps clearly demonstrate the localization of the doped regions on the symmetrical substrate after annealing. These results show that inkjet printing is a promising technique for the fabrication of localized poly-Si/SiOx passivating contacts in high-efficiency solar cells with high flexibility and simplicity.

Improving the passivation of contacts in silicon solar cells is crucial for reaching high‐efficiency devices. Herein, the impact of the contact work function on the obtained passivation is examined and quantified using a novel method—quasi‐steady‐state photoluminescence—which provides access to the surface saturation current density after metallization ( J 0s,m ). The obtained J 0s,m indicates an improvement of the surface passivation when contacts with high work function are applied onto Si wafers passivated with aluminum oxide, regardless of the wafer doping type. This improvement is mainly due to the amplification of the imbalance between the electron and hole concentrations near the Si interface. The passivation quality is reduced when using contacts with low work function in which the recombination rate increases via the charge‐assisted carrier population control. Herein, the vital importance of selecting suitable metals to minimize contact recombination in high‐efficiency solar cells is pointed.

Crystalline silicon (c-Si) solar cells using interdigitated back contact (IBC) configurations are one of the most promising candidates to reach the practical efficiency limits of c-Si solar cells. However, the complexity of the process flow hinders the mass production of the IBC cells with conventional doped regions. One of the simple fabrication methods is to introduce the dopant-free carrier-selective contacts, which utilizes the fabrication processes with low temperature, e.g., the thermal evaporation or the spin coating. In this paper, we investigated efficiency close to 20% silicon IBC solar cells with dopant-free asymmetric hetero-contacts. In this solar cell configuration, the high work function material MoOx was chosen as the hole transporting layer, while the low work function material LiF was chosen as the electron transporting layer, respectively. The simulation results indicate that the perspective efficiency exceeding 22% for this type of cells is achievable with the optimized pitch width and improved passivation quality of the contacts, which has a great potential for the industrialization of IBC solar cells with simple fabrication processes.

Si photocathode with industrially relevant charge selective passivation and physically deposited earth-abundant catalyst is developed with an efficiency above 10%. Solar-to-hydrogen efficiency of 17% is achieved by combining perovskite PV in tandem.

Defects and impurities in silicon limit carrier lifetimes and the performance of solar cells. This work explores the use of fluorine to passivate defects in silicon for solar cell applications. We present a simple method to incorporate fluorine atoms into the silicon bulk and interfaces by annealing samples coated with thin thermally evaporated fluoride overlayers. It is found that fluorine incorporation does not only improve interfaces but can also passivate bulk defects in silicon. The effect of fluorination is observed to be comparable to hydrogenation, in passivating grain boundaries in multicrystalline silicon, improving the surface passivation quality of phosphorus-doped poly-Si-based passivating contact structures, and recovering boron-oxygen-related light-induced degradation in boron-doped Czochralski-grown silicon. Our results highlight the possibility to passivate defects in silicon without using hydrogen and to combine fluorination and hydrogenation to further improve the overall passivation effect, providing new opportunities to improve solar cell performance.

This work explores the use of fluorine to passivate bulk defects in silicon. We present a simple method to incorporate fluorine atoms into the silicon bulk by annealing the sample with a thin thermally evaporated fluoride overlayer. It is found that fluorine incorporation can yield a comparable effect as hydrogenation, in passivating grain boundaries in mutlicrystalline silicon and reducing recombination strength of dislocation clusters in mono-like silicon. Moreover, we monitor the temperature dependence of the passivation reaction of hydrogenation and fluorination, using a micro-photoluminescence spectroscopy system with a temperature-controlled stage. It is found that the hydrogenation reaction occurs at the annealing temperature around 450 ° C, where a higher temperature above 500 ° C is required to activate the fluorination effect. The work provides new opportunities to improve solar cell performance.

Polycrystalline silicon (poly-Si) passivating contacts are promising technologies to promote the efficiency of silicon solar cells, due to their low carrier recombination and low contact resistivity. In this work, we present phosphorus spin-on doping as an alternative doping method to fabricate high performance poly-Si passivating contacts. The influences of thermal treatments and intrinsic amorphous Si thickness on poly-Si passivating contact quality were investigated. A high implied open-circuit voltage of above 730 mV together with a low contact resistivity below 4 m Omega.cm(2) were obtained for 100 - 230 nm thick poly-Si layers after a thermal treatment at 975 degrees C for 60 min followed by a forming gas annealing. The promising results presented in this work imply that phosphorus spin-on doping can be an effective doping method alternative to conventional POCl3 diffusion.

Adv. Energy Mater. 2020, 10, 1903553 In the original manuscript, the spelling “Anita Ho-Ballie” is incorrect. The correct spelling is, “Anita Ho-Baillie” The authors apologize for any inconvenience caused.

Passivating contacts for silicon solar cells can be fabricated by depositing a layer of intrinsic amorphous silicon (a-Si) by the plasma-enhanced chemical vapor deposition (PECVD) onto an oxidized silicon wafer, followed by a thermal POCl3 diffusion process. This article describes the influence of the main PECVD parameters, power and pressure, on the electrical performance of such phosphorus-doped polysilicon (doped-Si/SiOx) passivating contacts. We characterize their properties in terms of the passivation quality and carrier selectivity for different PECVD powers and pressures. The deposition power settings from 350 to 800 W are tried, the highest iVoc value of 721 mV is achieved at a power of 500 W. The higher deposition powers (≥650 W) lead to blistering issues and possible interface damage, while a lower deposition power (350 W) leads to incomplete decomposition of the precursor gas, resulting in a lower passivation quality. Meanwhile, the power has a marginal impact on the contact resistivity. On the other hand, the deposition pressure has only a slight impact on the passivation quality, while significant changes are observed on the contact resistivity. A lower pressure (0.1 mbar) leads to a higher contact resistivity, while the low and consistent contact resistivity values of 5.8 mΩ·cm 2 are obtained at the pressures above 0.2 mbar.

This paper describes the influence of plasma enhanced chemical vapor deposition (PECVD) deposition temperature on heavily doped silicon based (doped-Si/SiOx) passivating contacts for silicon solar cells. The doped-Si films are obtained by PECVD intrinsic amorphous silicon (a-Si) and a subsequent thermal POCl3 diffusion process. By changing the deposition temperature of PECVD, a-Si films with different degrees of crystallinity and density can be obtained. These differences between the a-Si films result in different properties of the passivating contacts in terms of passivation quality and carrier selectivity. By exploring a range of PECVD deposition temperatures from 250 degrees C to 470 degrees C, the best passivation quality is obtained at a temperature of 420 degrees C. On the other hand, the contact resistivity decreases with increasing deposition temperature. After studying the a -Si properties and the resulting passivating contact properties, we obtain optimal passivating contacts with a high implied open-circuit voltage (iV(oc)) of 742 mV and a low contact resistivity rho(c) of 6.4 m Omega.cm(2).