Tunnel Oxide Passivated Contact Research Articles

The Influence of Soldering Flux on Stability of Heterojunction and TOPCon Solar Cells

ABSTRACTSilicon heterojunction technology (HJT) and tunnel oxide passivated contact (TOPCon) solar cell technologies are expected to dominate the photovoltaic market in the coming years. However, there are still some concerns about the long‐term stability of these technologies. This work examines the effects of two widely used commercial soldering fluxes (Flux A and Flux B) on the stability of commercial silicon HJT and TOPCon solar cells. The soldering flux was applied to the solar cells, and the solar cells were annealed at 85°C under a relative humidity (RH) of 0%. The investigated TOPCon solar cells were found to be stable; however, significant degradation was observed in the HJT solar cells after only 50 h. The efficiency of the HJT cells decreased by ~61%rel with Flux A and ~55%rel with Flux B, respectively. We attribute part of the observed degradation to pores present in the HJT cell metallisation after printing, which allow the soldering flux to easily penetrate the contact and subsequently react with the paste constituents. In addition, we find that the indium tin oxide (ITO) layer is very sensitive to soldering flux, showing major cracks and significant peeling after 50 h of annealing. Consequently, this work shows that some soldering flux can react with the ITO layer, without requiring the presence of water. This suggests that certain types of soldering flux can harm HJT solar cells even after encapsulation without the need for moisture ingress. Therefore, paying more attention to the choice of soldering flux is essential, especially when working with HJT cells. It is strongly recommended that users perform comprehensive component analysis testing on soldering fluxes before their official use rather than solely relying on datasheets provided by suppliers.

Research progress in passivation layer technology for crystalline silicon solar cells

Under the background of rapid advancements in photovoltaic technology, crystalline silicon (c-Si) solar cells, as the mainstream photovoltaic devices, have gained significant research attention for their excellent performances. In particular, silicon heterojunction (SHJ) solar cells, TOPCon (Tunnel Oxide Passivated Contact), and PERC (Passivated Emitter and Rear Cell) represent the cutting-edge technologies in c-Si solar cells. The surface passivation layer of crystalline silicon solar cells, as one of the key factors to improve cell performances, has been closely linked to the development of crystalline silicon solar cells. Due to the complex mechanism of passivation layer and the high demand of experimental research, it is challenging to achieve high quality surface passivation. This paper comprehensively reviews the key issues and research progress in interface passivation technologies for SHJ, TOPCon, and PERC solar cells. Firstly, the research progress of key technology breakthrough of SHJ solar cell is reviewed systematically, and the influences of growth conditions and doping layer on the passivation performances of SHJ solar cell are discussed in detail. Secondly, the important strategies and research achievements for improving the passivation performances of TOPCon and PERC solar cells in the past five years are systematically described. Finally, the development trend of passivation layer technology is prospected. This review offers valuable insights for future technological improvements and performance enhancements in c-Si solar cells.

Mitigating Passivation Layer Damage and Lowering Contact Resistivity of TOPcon Solar Cells Through Low PbO Content Ag Paste.

The development of front-side pastes suitable for devices with high sheet resistance such as tunnel oxide passivated contact (TOPCon), is of great significance but remains a considerable challenge. The optimization of the Ag-Si contact interface is crucial for enhancing contact and improving the efficiency of these devices. This work investigates the front-side Ag pastes with low Al content (<2 wt.%) and different frit compositions for TOPCon. It is found that the paste with low-addition frit effectively prevents excessive etching of passivation layers and minimizes additional damage to boron emitters while ensuring favorable contact. Meanwhile, the lowly FT (fire through) paste promotes Ag nanoparticles with larger particle sizes and higher quantities in the interfacial glass, thereby enhancing the conductivity of the interfacial glass and reducing contact resistivity. A low contact resistivity of ≈1 mΩ·cm2 and superior photovoltaic conversion efficiency of 25.19% are achieved on TOPCon with a sheet resistance of ≈350 Ω/□. This work demonstrates the application potential of Ag-Al paste with low Al content suitable for high sheet resistance emitters by modulating the Ag-Si interface structure. The coupling between microstructure and device performance is elucidated offering an innovative approach for developing silver paste suitable for high sheet resistance TOPCon.

Bilayered Phosphorus‐Doped Polysilicon Passivating Contact Structures for TOPCon Solar Cell Applications

ABSTRACTThe use of single‐layer polysilicon (poly‐Si) in tunnel oxide passivated contact (TOPCon) structures has demonstrated excellent passivation and contact performance. However, commercial TOPCon solar cell fabrication requires screen‐printing and cofiring techniques for electrode preparation. The single‐layer structure is less efficient at preventing metal atoms in the electrode paste from penetrating the silicon bulk. Furthermore, the uniformity of doping concentration and crystallinity within this structure poses challenges as it fails to optimally meet the intricate requirements for achieving superior performance in terms of passivation, contact, and mitigating parasitic absorption. In this study, the deposition process of the amorphous silicon (a‐Si) precursor layer using an in‐line magnetron sputtering system incorporated an additional plasma oxidation step, resulting in a bilayer poly‐Si structure with the newly introduced SiOx acting as a partition. Detailed investigations were conducted into the passivation quality, contact resistivity, crystallinity, and the distribution of critical atoms in the bilayer structure. Subsequently, the bilayer configuration was utilized in the manufacturing process of TOPCon solar cells. These efforts resulted in a notable enhancement in open‐circuit voltage (Voc) and short‐circuit current (Isc), leading to a 0.06% efficiency improvement, based on the average performance of ~200 cells per group.

Nano-size Joule-Heating to Achieve Low-Ohmic Ag-Si Contact on Boron Emitters of n-TOPCon Solar Cells.

Over the past decade, Tunnel Oxide Passivated Contact (TOPCon) solar cells have emerged as a leading technology for high-efficiency silicon solar cells. Conventional metallization processes using silver/aluminum (Ag/Al) pastes encounter significant hurdles due to reliability risks and insufficient contact quality. Recent advancements in laser-induced metallization technologies, particularly laser-enhanced contact optimization (LECO), offer promising solutions. However, the mechanism of silver-silicon (Ag-Si) contact formation on the P+ emitter of TOPCon cells via LECO processing remains incompletely understood. This study designs and prepares two types of glass frits (GF-A and GF-B) for TOPCon cells and investigates the electrical properties of corresponding devices. Advanced techniques are employed to examine the Ag-Siinterfaces. The results demonstrate that GF-A-based TOPCon cells (Cell-A) outperformed GF-B-based cells (Cell-B) due to the construction of a current-confined Ag-Si interface. A composite conductive model for the Ag-Si interfaces by LECO treatment is introduced, revealing the nano-size Joule-heating to achieve the Ag-Si eutectic structure as the underlying formation mechanism. This work contributes to the understanding of metal-silicon contact optimization in solar cells and introduces novel methodologies for laser-induced synthesis and micro-nano interface engineering.

TOPCon Solar Cells With Al-Free Ag and Cu Metallization

This work presents an approach to lower the silver consumption of screen printed TOPCon (Tunnel Oxide Passivated Contact) solar cells by reducing and partially replacing the silver by low cost copper metallization paste. On the solar cells front side an adapted process sequence enables the use of a pure Ag paste, which compared to the industrially established AgAl paste offers a better conductivity and respectively requires less laydown to enable similarly low grid resistance. On the solar cells rear side the conductivity of the metal grid is accomplished by a copper paste which is realized within a print-on-print step on top of the Ag contact layer with minimized laydown. A reduction in Ag paste consumption by 40% to less than 9 mg/ Wp without sacrificing conversion efficiency seems achievable and can enable a significant cost reduction for TOPCon solar cells.

Reactive Force-Field Molecular Dynamics Study for Analysis of Silicon Nanocrystal Formation Process in Silicon Oxide Film

Recently, Tunnel Oxide Passivated Contact (TOPCon) solar cells using ultra-thin silicon oxide (SiO x ) films as passivation films have attracted attention due to the high conversion efficiency of 25.7% [1]. Generally, thick SiO x films exhibit excellent passivation performance and lead to long-term reliability of the solar cells[2]. However, in TOPCon solar cells, the thickness of the passivation film is limited to 1~2 nm due to the high electrical resistance of the SiO x film. Therefore, a new SiO x film (named NATURE contact) with improved conductivity through silicon nanocrystals (Si NCs) have been developed by Tsubata et al. [3]. The left figure shows the structure of NATURE contact. It consists of three SiO x layers with different oxygen concentrations. The Si NCs formed in the thin Si-rich layer in the center functions as a carrier transport pathway. The passivation film with the NATURE contact has shown a good passivation performance and conductivity even for relatively thick SiO x films. Since the effects of multidimensional process parameters during NATURE contact formation have been neither elucidated nor optimized, there is significant room for performance improvement in NATURE contact. Therefore, it is of crucial importance to understand the atomic level growth process of Si NCs during formation of NATURE contact and its impact of the oxygen concentration and temperature.We employed Reactive force-field molecular dynamics (ReaxFF MD) method, which reproduces chemical reactions using a bond order-dependent concept. The method has been used in studies such as Si deposition simulations [4]. The periodic boundary conditions were applied to the simulation box for all directions in the size of 65 Å × 40 Å × 45 Å. Crystalline silicon was placed throughout the simulation box and the atoms of the simulated Si NC section were fixed in the center of the box. Crystals other than the fixed portion are then made amorphous using the Melt-Quench method. Finally, the fixation was released to allow the entire box to react. Crystallinity was evaluated by the average radius calculated from the number of atoms constituting the crystal. It is noted that the average radius is evaluated up to 25 Å due to the size of the simulation box. Annealing was performed in the following three processes: pre-moistening, amorphization, and crystal growth. We varied the temperature of crystal growth at 1500 - 2500 K and the oxygen concentration at 0 - 5 %. We investigated the effects of temperature and oxygen concentration on the growth of Si NCs in a-SiO x .The right figure shows the transition of the mean radius of the Si NCs at different temperatures. As a result, when the temperature was varied, a peak in the size of crystal growth was observed at 2250 K, and the crystals disappeared at 2500 K. The trend of maximum crystal growth at a certain temperature and the qualitative agreement were experimentally confirmed [5]. This result suggests that the change in the size of Si NCs occurred because the kinetic energy of Si atoms is larger than the energy barrier required from a-Si to c-Si. The initially placed Si NC of 269 atoms was appropriately shaped or grown. This is consistent with the nucleation theory[6]. When the oxygen concentration was increased, no crystal growth was observed. Experiments have shown that increasing oxygen concentration tends to suppress crystallization [3]. This result suggests that the change in the size of Si NCs was caused by the interdiffusion of silicon and oxygen.

Ultrathin Self-Assembled Monolayer for Effective Silicon Solar Cell Passivation.

Passivation technology is crucial for reducing interface defects and impacting the performance of crystalline silicon (c-Si) solar cells. Concurrently, maintaining a thin passivation layer is essential for ensuring efficient carrier transport. With an ultrathin passivated contact structure, both Silicon Heterojunction (SHJ) cells and Tunnel Oxide Passivated Contact (TOPCon) solar cells achieve an efficiency surpassing 26%. To reduce production costs and simplify solar cell manufacturing processes, the rapid development of organic material passivation technology has emerged. However, its widespread industrial production is hindered by environmental safety concerns, such as strong acid corrosion and biological and ecological safety issues. Here, we discovered a low-cost self-assembled monolayer (SAM) hole-selective transport material known as 2PACz ([2-(9H-carbazol-9-yl) ethyl] phosphonic acid) with phosphate groups to form c-Si solar cells for the first time. The ultrathin film of 2PACz with phosphate groups can establish strong and stable P-O-Si bonds on the silicon surface. Meanwhile, like 2PACz, a uniform ultrathin film with a carbazole function group can offer electron-localizing and thus hole-selective properties, which provides ideas for studying dopant-free silicon solar cells. As a result of such interfacial passivation engineering, it plays an important role in repairing porous structures, such as pyramid-textured silicon surfaces, and cutting losses during the commercialization of c-Si solar cells. Crucially, this advancement offers insights for the development of new high-efficiency ultrathin film passivation methods in the postsilicon era.

Tunnel silicon oxynitride phase transformation for n-type polysilicon passivating contacts in crystalline silicon solar cells

The study investigates the fabrication and characterization of tunnel oxynitride (TON) layers produced using Plasma-Enhanced Chemical Vapor Deposition (PECVD) at different pressure and power variations. The aim is to explore TON layers as potential substitutes for conventional SiO2 in Tunnel Oxide Passivated Contact (TOPCon) solar cells. Foe this purpose, an effective oxide thickness (EOT) of 1.1–1.2 nm and 1.5–1.6 nm has been achieved by treating the TON samples with NH3 and N2 gas plasma, respectively. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed critical variations in the chemical bonding within TON layers, which exhibit different properties based on the deposition conditions. The presence of nitrogen-nitrogen and nitrogen–hydrogen bonds is prominently influenced by changes in the PECVD parameters, directly affecting the layer’s optical and electronic properties. Notably, the presence of hydroxyl (O–H) and amino (NH2) groups within the TON structure suggests an improvement in surface passivation, essential for optimizing solar cell performance and durability. A lifetime of 737 and 823 μs has been recorded for N2 and NH3 samples, compared to the NAOS 710 μs reference sample. NH3 plasma-treated samples show an improved iVoc of 736 mV, indicating better phase transformation and passivation quality than N2 plasma treatment and the NAOS reference sample.

Unveiling the origin of metal contact failures in TOPCon solar cells through accelerated damp-heat testing

Tunnel oxide passivated contact (TOPCon) solar cells are expected to dominate the global photovoltaic market in the coming decade thanks to rapid advancements in power conversion efficiency (PCE). However, there are concerns about the reliability of TOPCon modules, particularly in hot and humid conditions. The current module-level fundamental analysis strategies for TOPCon solar cells provide too slow feedback for rapid process development. This study explores the degradation of metal contacts in TOPCon solar cells under accelerated testing conditions of 85 °C and 85 % relative humidity (DH85). The degradation was induced by two commonly used sodium-related salts, sodium bicarbonate (NaHCO3) and sodium chloride (NaCl), in the testing of the solar cells. When applied to the front side, NaHCO3 caused a ∼5%relPCE reduction after 100-h DH85 exposure, while NaCl leads to a more significant ∼92%relPCE reduction. The primary cause of degradation is a considerable increase in series resistance (Rs), likely due to electrochemical reactions within the Ag/Al paste. When the salts are applied to the rear of the TOPCon solar cell, the degradation becomes more complex. NaHCO3 increases recombination and results in a deterioration of the contact, resulting in a ∼16%relPCE reduction after 100-h DH85 testing. Conversely, NaCl primarily causes a decline in open-circuit voltage (Voc) and a ∼4%relPCE loss. This manuscript primarily investigates degradation mechanisms related on the rear side, with a focus on significant oxidation occurring at the interface between Ag and Si. These findings highlight the susceptibility of TOPCon solar cells to contact corrosion, emphasizing the electrochemical reactivity of metallisation as a potential risk for long-term TOPCon module operation. This study provides crucial insights into TOPCon cell degradation mechanisms, which are essential for optimising performance and enhancing the long-term reliability of TOPCon modules.

Highly passivated TOPCon bottom cells for perovskite/silicon tandem solar cells

Tunnel oxide passivated contact (TOPCon) silicon solar cells are rising as a competitive photovoltaic technology, seamlessly blending high efficiency with cost-effectiveness and mass production capabilities. However, the numerous defects from the fragile silicon oxide/c-Si interface and the low field-effect passivation due to the inadequate boron in-diffusion in p-type polycrystalline silicon (poly-Si) passivated contact reduce their open-circuit voltages (VOCs), impeding their widespread application in the promising perovskite/silicon tandem solar cells (TSCs) that hold a potential to break 30% module efficiency. To address this, we have developed a highly passivated p-type TOPCon structure by optimizing the oxidation conditions, boron in-diffusion, and aluminium oxide hydrogenation, thus pronouncedly improving the implied VOC (iVOC) of symmetric samples with p-type TOPCon structures on both sides to 715 mV and the VOC of completed double-sided TOPCon bottom cells to 710 mV. Consequently, integrating with perovskite top cells, our proof of concept of 1 cm2 n-i-p perovskite/silicon TSCs exhibit VOCs exceeding 1.9 V and a high efficiency of 28.20% (certified 27.3%), which paves a way for TOPCon cells in the commercialization of future tandems.

Optimization of rear surface morphology in n-type TOPCon c-Si solar cells

Tunnel oxide passivated contact (TOPCon) crystalline silicon (c-Si) solar cells have attracted much attention because of their superior electrical properties such as the lower contact resistivity and better interface passivation at high temperatures. However, the TOPCon c-Si solar cells also have room for further improvement in optical performance, and the embodiment of optical advantages needs to be matched synchronously in electrical aspect. Here, the rear silicon pyramids with different angles have been achieved through solution corrosion to maximize the light absorption in the c-Si substrate. The light absorption for the pyramid angle of less than 30° is better. Compared with the cell samples with rear pyramid for a certain angle, the samples with flat back surface possess better surface passivation, and the contact resistivity can be reduced effectively by increasing the phosphorus doping concentration and adjusting the annealing temperature. Furthermore, the TOPCon c-Si solar cells with flat rear surface covered by 70 nm poly-Si have been demonstrated to increase the conversion efficiency by about 0.15 % vs. the counterpart for poly-Si of 130 nm thickness, and the improvement is mainly due to the increase of JSC and FF by 0.07 mA/cm2 and 0.72 %, respectively.

22.56% total area efficiency of n-TOPCon solar cell with screen-printed Al paste

Screen-printing Ag paste on the rear side of the Tunnel Oxide Passivated Contact solar cells (TOPCon) is still the mainstream method to form electrodes. However, the high price of precious metals increases the cost of TOPCon cells. Al is a cheap and high-performance conductor, and its work function is compatible with the rear side of TOPCon cells. In this study, we used a UV pulse laser (355 nm, 10 ps) to ablate the rear side SiNx passivation layer of TOPCon cells and then printed Al paste with different weight percentages of silicon (Si-wt.%) on the phosphorus-doped polycrystalline silicon (n+-poly-Si) layer to reduce the cost. We investigated the damage mechanism of laser on SiOx/n+-poly-Si/SiNx passivation structure and the contact mechanism between Al paste and n+-poly-Si layer. The results show that the Voc of SiOx/n+-poly-Si/SiNx passivation structure reduced about 6–7 mV when the laser energy density was 0.431 J/cm2. We got the best electrical performance of TOPCon cells printed with Al paste (25 wt%-29 wt% silicon). The open-circuit voltage (Voc) and the conversion efficiency (Eff), have reached 663.60 mV and 22.56 % respectively. Although the efficiency was 9.40 % relative lower than that of TOPCon cells printed with Ag paste, but the cost of Al paste only accounted for 10 % of Ag paste. In the future, the highest Eff of TOPCon solar cells printed with Al paste on the rear side are expected to reach the commercial TOPCon based on Ag paste, which applies laser doping selective emitter technology (SE) and bifacial poly-Si passivation structure.

Electrical Performance, Loss Analysis, and Efficiency Potential of Industrial‐Type PERC, TOPCon, and SHJ Solar Cells: A Comparative Study

ABSTRACTCurrently, the efficiency of p‐type passivated emitter and rear contact (PERC) cells has been growing at an absolute efficiency of 0.5% per year and has reached 23%–23.5% in mass production while getting closer to its theoretical efficiency limit. n‐Type tunnel oxide passivated contact (TOPCon) and silicon heterojunction (SHJ) cells with their superior “passivating selective contacts” technology were the most interesting photovoltaics (PV) technology in the industry. The effect of different passivated contact layers with respect to their influence on the J0, J0,metal, ρc, and the carrier selectivity (S10) and the loss analysis and efficiency potential of industrial‐type PERC, TOPCon, and SHJ solar cells were studied and compared. The results showed that TOPCon structure with a high passivation performance and good optical performance is more suitable for bifacial solar cell and the highest theoretical limiting efficiency with metal shading on the n‐type Si wafer (ηb,e,h,m,max) can be achieved to 27.62%. Although SHJ structure with the highest passivation performance but the worst optical performance owing to the parasitic absorption of a‐Si:H layer and high contact resistivity, the value of ηb,e,h,m,max is 0.7% lower than that of TOPCon solar cells. PERC structure has superior optical performance than SHJ structure, but due to poor passivation performance, the ηb,e,h,m,max is only 26.42%. The next‐generation products may be heterojunction back‐contact (HBC) and TOPCon back‐contact (TBC) cells with high ηb,e,h,m,max of 28.12% and 27.99%, respectively. Exploiting a perfect passivation of the noncontact area, the wide process window and low cost are required and transferring these new concepts to industrial solar cell production will be the next major challenge.

Advancing nickel seed layer electroplating for enhanced contact and passivation performance in TOPCon solar cells

Electroplating copper technology offers advantages such as low cost, good conductivity, and a simple process, making it a promising solution in the photovoltaics (PV) field. However, despite its effectiveness in reducing silver consumption, a significant challenge arises from suboptimal electrical contact between metal electrodes and the polycrystalline silicon films, limiting the application of electroplating techniques in tunnel oxide passivated contact (TOPCon) solar cells (SCs). In this study, we propose a simple method to enhance the quality of electrodeposited metals and improve contact performance with polycrystalline silicon films by lowering the electrodepositing temperature for nickel seed layer. Additionally, we optimize contact properties by modulating nickel deposition time and annealing temperature. This process results in excellent physical and electrical contact performance, achieving the lowest contact resistivity of 0.19 mΩ cm2 and the improved adhesion strength. Ultimately, TOPCon SCs using low-temperature plated seed nickel and copper metal electrodes achieve an efficiency of 23.90%, which is attributed to advance the application of optimal nickel seed layer electroplating.

Tunnel oxide passivating contact enabled by polysilicon on ultra-thin SiO2 for advanced silicon radiation detectors

Conventional silicon junction detectors encounter significant carrier recombination within the heavily doped p+ and n+ layers, as well as beneath the metal contact regions, creating the so-called “dead layers”, especially on the detector side. In this study, we present the tunnel oxide passivating contact with doped polysilicon on oxide, which demonstrates exceptional surface passivation and carrier selectivity. The key innovation lies in an ultra-thin (~ 1.5 nm) interfacial oxide layer that facilitates efficient majority carrier transportation via tunneling while effectively block minority carriers. Remarkably low saturation current densities, ranging from 5 to 10 fA/cm2 even with the metal contact, underscore the superiority of both n-type and p-type tunnel oxide passivating contacts. In contrast, conventional p–n junction or high-low junction exhibit saturation current densities ranging from 10 to 90 fA/cm2 in the studied p+ and n+ layers with surface passivation schemes due to Auger recombination and surface recombination, and 1000–6000 fA/cm2 with metal contacts due to intense metal-induced recombination at the interface. These findings indicate the potential and superiority of implementing n-type tunnel oxide passivating contact on the detector side and p-type contact on the back side for advanced silicon radiation detectors. This approach would enable thorough collection of generated charge carriers along the track of incident ionizing radiation particles, leading to improved energy resolution and reduced noise levels.

Optimizing phosphorus-doped polysilicon in TOPCon structures using silicon oxide layers to improve silicon solar cell performance

Tunnel Oxide Passivated Contact (TOPCon) technology is one of the most influential and industrially viable solar cell technologies available today. Improving the quality of passivation contact has become a central focus of current research. Although the conventional monolayer polycrystalline silicon method is highly effective in TOPCon solar cells, it is limited by doping inhomogeneity, which impairs the passivation and electrical properties, and the cell's photovoltaic conversion efficiency remains suboptimal. To address this issue, this study investigates the deposition of two layers of silicon oxide and two layers of in-situ doped phosphorus amorphous silicon, termed double poly-Si/SiOx structures, on n-type silicon wafers using plasma-enhanced chemical vapor deposition (PECVD). The effectiveness of the structure was confirmed through various characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Key findings indicate that the double-polysilicon structure significantly enhances the uniformity of phosphorus doping, improving the carrier lifetime of the cell and reducing the contact resistance. As a result, the average efficiency in the final production stage has a conversion efficiency gain of 0.23 % over the baseline group. This study underscores the potential of this PECVD methodology to advance the fabrication of high-efficiency solar cells by providing significant improvements in passivation, doping uniformity, and overall cell performance.

Preparation of Al2O3 thin films by RS-ALD and edge passivation application for TOPCon half solar cells

A rotary spatial atomic layer deposition (RS-ALD) method is proposed for the preparation of high-quality Al2O3 thin films and its application to the edge passivation of tunnel-oxide passivated contact (TOPCon) half solar cells. The high- quality Al2O3 thin films were prepared on silicon wafers by optimizing the process conditions with a process pressure of 4 Torr and a trimethylaluminum (TMA, (CH3)3Al) flow rate of 300 sccm. The Al2O3 thin films were annealed to analyse the transformation of the film crystal structure, surface morphology, and passivation properties. Compared to the half solar cells without edge passivation, the efficiency of the cell with only deposited Al2O3 increased by 0.098 %, and the module power increased by 3.08 W. The efficiency of the cell with deposited Al2O3 + annealing increased by a further 0.021–0.119 %, and the module power increased by a further 0.68–3.76 W.

Laser damage and post oxidation repair performance of n-TOPCon solar cells with laser assisted doping boron selective emitter

Boron laser-assisted doped selective emitter (LDSE) is a research hotspot in the mass production of N-type tunnel oxide passivated contact (TOPCon) silicon solar cells. Consequently, it is critical to investigate the damage and repair of laser-assisted doped selective emitter. Through simulation, a surface temperature of silicon rises to over 1414 °C during the laser-assisted doping process, which causes silicon to melt and recrystallize more quickly, and increases the solid solubility of B atoms. Meanwhile, the surface pyramid structure was partially destroyed or even collapsed. The results showed that the peak intensity of (211) crystal planes decreased while the peak intensity of (400), (311), and (220) crystal planes increased. This led to an increase in surface defects and suspension bonds, resulting in an increase in J0,passivated up to 246.3 fA/cm2. The laser-induced damage can be successfully repaired by the post-oxidation process, reducing J0,passivated to 45.07 fA/cm2. The Quokka simulation indicates that a laser pulse fluence of 2.78 J/cm2 can increase the efficiency of the LDSE cell by 0.31 %. It does not necessarily lead to the greater efficiency gains with higher laser pulse fluence owing to the increase in surface damage. Exploiting the laser assisted doping method with a minimal surface damage, a wide process window and low cost will be the next major challenge.

The differences between the hydrogenation by means of photon-injection and electron-injection for N-type tunnel oxide passivated contacts solar cells

Tunnel Oxide Passivated Contact (TOPCon) solar cells have received widespread attention in recent years, especially in improving conversion efficiency. This paper investigated the impact of hydrogenation technology using photon-injection (HPI) and electron-injection (HEI) processes on TOPCon solar cells, highlighting the higher improvement effect and broader application scope of HPI compared to HEI. In TOPCon cells, several methods are available to prepare the tunneling oxide layer, such as plasma oxidation (PO) and indirect thermal oxidation (TO). The research results indicated that significant improvement differences could be observed when utilizing the HEI treatment for TOPCon solar cells prepared by PO and TO methods, with values of 0.133%abs. and −0.039%abs., respectively. Meanwhile, HPI treatment induced a more significant efficiency improvement for these two types of cells, and the increase in efficiency is 0.247%abs. and 0.244%abs., respectively. The experimental results demonstrated that the passivation effect for TOPCon solar cells prepared by PO and TO methods remained almost the same under the HPI treatment, and the improvement effect is less dependent on the tunnel oxidation technique used. Thus, the different passivation effects between HPI and HEI were further investigated, and the reason for the difference was attributed to the charge states and concentrations of hydrogen and non-equilibrium carriers during the hydrogenation. The results provided an improved scheme for enhancing the efficiency of TOPCon solar cells, shedding light on the role of HPI and HEI in the passivation process. This work brings further insights to TOPCon solar cells.