Tunnel Oxide Passivated Contact Research Articles

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.

Optimizing the metallization process for high fill factor of n-type crystalline silicon TOPCon solar cells

The primary challenge in solar cell manufacture concerning the metallization process is the need to achieve a balance between the electrical and optical performance of the metal contacts as the contribute to shading and the series resistance (Rs) of solar cells. Addressing these challenges with the optimization of the metallization process is crucial for achieving a high fill factor (FF) in solar cells, as FF is a key parameter indicating the quality and efficiency of a solar cell. An impact of different snap-off, distances between mask and cells, of n-type TOPCon (Tunnel Oxide Passivated Contact) solar cells during the screen-printing process was conducted. This experiment employs testing and analysis to determine the most effective snap-off distance that minimizes the Rs variability, resulting in an overall enhancement in cell efficiency. The smaller snap-off distance can lead to better performance in n-TOPCon solar cells due to finer lines, uniform contacts, and lower Rs. The I-V characteristics of 1.4 mm are Jsc of 39.58 mA/cm2, Voc of 684.63 mV, FF of 80.54 %, and power conversion efficiency (PCE) of 21.83 %, respectively. In addition, dark I-V measurement is essential for diagnosing performance issues; we got shunt resistance (Rsh) of 4.97 x 106 Ω which is the highest value that indicates minimal Rs of 0.3 Ω. As a result, it is a potential strategy for n-TOPCon solar cell improvements.

Buyer aware: Three new failure modes in TOPCon modules absent from PERC technology

The n-type tunnel oxide passivated contact (TOPCon) technology is going to be the leading industrial technology in 2024. However, there are still concerns about the reliability of TOPCon when used in the field, especially in glass/backsheet modules. This work investigates the impact of damp heat (DH) on the performance TOPCon and PERC glass/backsheet modules by varying bills of materials (BOM), such as polyolefin elastomer (POE), ethyl-vinyl acetate (EVA), and polymer backsheet options. It is found that PERC modules remain stable, with a maximum power loss (Pmax) of only 1–2%rel after 1000 h of DH testing, regardless of the BOM used. However, TOPCon modules experienced significant degradation with a drop in Pmax ranging from 4 to 65%rel after the same testing duration. Despite utilizing POE, an expensive encapsulant with a significantly lower water vapour transmission rate than EVA and devoid of acetic acid formation, a severe performance decline was observed in a specific POE variant within TOPCon modules, with a loss of power of up to 65%rel. Three types of failures were observed in TOPCon modules: point-localized failure, failure at/around the interconnection of ribbon wires and busbars, and failure throughout the whole area of cells/modules. These failures likely result from electrochemical reactions involving moisture, cell metallization, ribbon wires, contaminants, soldering flux, and additives released from POE. The observed findings underline two crucial points: 1) the vulnerability and potential failure of TOPCon solar cells when exposed to high humidity and contaminants, and 2) the high risk associated with certain POE types, which could potentially adversely affect TOPCon cells. Hence, it is crucial to exercise utmost caution and precision in handling and selecting encapsulation materials for TOPCon modules. Accordingly, urgent and extensive research efforts are crucial to substantially increase our comprehension and fortify the reliability of TOPCon cells against the pernicious effects of moisture and other contaminants.

Highly Transparent Oxygen‐Doped Poly‐Si with In‐situ N2O Oxidant for Poly‐Si Passivating Contacts in Perovskite/Silicon Tandem Solar Cells

Tunnel oxide passivated contact (TOPCon) silicon solar cells have been developed and transferred into industrial mass production, which is beneficial to the future production of perovskite/silicon tandem solar cells (TSCs) in a large scale. However, the doped polycrystalline silicon (poly‐Si) layer in the poly‐Si‐based passivating contact structure yields a profound optical loss from reflection and parasitic absorption, which obstacles the efficiency promotion of TSCs. In this work, the optical property of poly‐Si is improved by in‐situ oxygen incorporation using plasma enhanced chemical vapor deposition (PECVD) with nitrous oxide (N2O) as the oxygen source. The p‐type oxygen‐incorporated poly‐Si (poly‐SiOx) shows a reduced refractive index and extinction coefficient over 700–1200 nm wavelength, leading to a reduced reflection, a lower parasitic absorption and a higher transmission. After applying an optimized p‐type oxygen‐incorporated poly‐Si in the front‐side poly‐Si passivating contact structure of c‐Si bottom cell, the short‐circuit current density and efficiency of a perovskite/c‐Si tandem cell increases by ≈0.32 mA cm−2 and ≈0.8%, respectively, leading to 25.12% tandem cell efficiency.

Comparative Study on Energy Yield of Tunnel Oxide Passivated Contact (TOPCon) and Passivated Emitter and Rear Contact (PERC) Solar Cells and Analysis of Optimal Installation Method for Vertical Photovoltaics

AbstractPhotovoltaic (PV) installations have traditionally relied on a conventional south-facing orientation, which maximizes energy production at noon but has lower energy generation in the morning and afternoon. Vertical photovoltaic (VPV) systems have emerged as promising alternatives to address this inconsistency. Vertical photovoltaic systems can enhance energy generation by facing east in the morning and west in the afternoon. We compared the performance of n-tunnel oxide passivated contact (n-TOPCon) and p-passivated emitter and rear contact (p-PERC) cells in vertical photovoltaic systems to determine whether the optimal installation direction of bifacial vertical photovoltaics is east or west. Our findings indicated that n-TOPCon cells exhibited higher energy yields than p-PERC cells, with a difference of approximately 8%, attributed to the superior bifaciality and lower temperature coefficient of power of n-TOPCon. Additionally, the energy yield was higher for n-TOPCon modules when the front faced east, whereas the PERC modules performed better with a west-facing front. This contributes to the knowledge of the factors for energy production in vertical photovoltaic systems and the optimization of installation configurations.

Progress in TOPCon solar cell technology: Investigating hafnium oxide through simulation

In the realm of solar energy technology, exploring hafnium oxide (HfO2) in Tunnel Oxide Passivated Contact (TOPCon) solar cells is pivotal. This study delineates HfO2's evolution from semiconductor applications, highlighting its crucial role in enhancing TOPCon solar cell performance. Utilizing ATLAS Silvaco software, the study anticipates a 21.3% increase in charge carrier lifetime through optimized HfO2 layers, addressing challenges in interface engineering and scalability. Innovative research integrates hafnium oxide (HfO2) into TOPCon solar cells, marking a leap in photovoltaic technology. Utilizing ATLAS Silvaco simulations, it shows that HfO2 layers can significantly enhance cell performance, increasing charge carrier lifetime by 21.3% and potentially boosting efficiency by 25%. This underscores HfO2's advantages, like a higher dielectric constant and thermal stability, in improving solar cell efficiency and durability. Future efforts target refining deposition processes, projecting a 25% boost in overall power conversion efficiency (PCE). Emphasizing HfO2's significance in solar cell technology, this research contributes to global sustainable energy initiatives. Integrating HfO2 in TOPCon solar cells signifies a key achievement in harnessing clean, renewable energy. Upcoming research focuses on experimental validation, interface engineering, optimization, stability assessments, scalability, and collaborative studies, aiming to leverage HfO2's potential for elevating solar energy conversion technologies.

Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

The tunnel oxide passivated contact (TOPCon) concept has been the brightest star in the field of emerging passivating contact techniques for the last few years. It has shown great potential in industrial applications due to the overwhelming advantages of high device efficiency and low cost. Here, we introduce a novel crystallization method using ultrafast laser-annealing by scanning a laser spot onto the surface of hydrogenated amorphous silicon film in TOPCon solar cells. By circumventing the high-temperature environment of the conventional annealing process, it can prevent a large number of dopant atoms from penetrating inside the crystalline silicon (c-Si) substrate, reducing the Auger recombination. Moreover, we can conduct extensive experiments to clarify the optimal conditions, including laser-annealing modes and process parameters. The hydrogenation experiments reveal that direct appropriation of the traditional hydrogenation method is not applicable. An additional ‘dehydrogenation’ step proves necessary, indicating that the differences in hydrogen content within the films due to the divergence between the principles of laser-annealing and high-temperature annealing are probably responsible for this. Consequently, the proof-of-concept devices using laser-annealing technology realize a champion efficiency of 19.91%,highlighting an alternative technical route with substantial potential to achieve high-efficiency crystalline silicon solar cells.

High-efficiency TOPCon solar cell with superior P + and P++ layer via one-step processing

The boron diffusion process in the front field of N-type tunnel oxide passivated contact (TOPCon) solar cells is crucial for PN junction formation and the creation of a selective emitter. This study presents a theoretical model of boron diffusion in silicon using molecular dynamics. The research examines the mean square displacement and diffusion coefficient of boron atoms at varying temperatures, confirming their diffusion behavior. The simulations indicate predominant boron diffusion in the z-direction within the silicon matrix, with the diffusion depth being temperature dependent. The optimal temperature range for boron diffusion in silicon is identified as 950 °C to 1050 °C. Using boron-doped silicon paste and boron trichloride as dopants, thermal diffusion experiments were conducted to fabricate the front-field PN junction (p+ layer) and selective emitter (p++ layer) by one step. Subsequent processing and performance evaluation were performed on a production line. Experimental findings reveal a decrease in boron diffusion at higher temperatures, reduced sheet resistance, increased doping concentration, and deeper junction formation. The ideal boron concentration in the p+ layer is 8.68 × 1018 atom/cm3 with a depth of 0.53 μm, while the p++ layer is 2.35 × 1019 atom/cm3 and 0.82 μm. The efficiency of the optimized TOPCon + cell production line reaches up to 25.17 %, marking an improvement of 0.23 % over the standard cell production line. This research contributes to elucidating the mechanism of boron diffusion and offers insights for enhancing the efficiency of TOPCon solar cells.

Bi-layer in-situ phosphorus doped poly-Si films by PECVD for blistering-free high-efficiency industrial TOPCon solar cells

The passivating contact concept stands out as one of the most promising and industrially viable photovoltaic (PV) technologies. Further improving the quality of physical contact has become a focus of ongoing research. The film blistering issue has been identified as one of the major bottlenecks for the polysilicon (poly-Si) films deposited by the PECVD approach. In this study, we investigated how the in-situ phosphorus (P) doping level within the poly-Si films contributes to the occurrence of blistering. Our investigations into the film blistering mechanisms reveal that a high in-situ P-doping suppresses hydrogen release levels and reduces the accumulation of residual stress during annealing, which leads to the blistering-free appearance, especially observed in heavily P-doped poly-Si films. However, as excessive P-doping could weaken the interfacial passivation quality, we propose a bi-layer structure of P-doped poly-Si films which allows the doping profile to be tailored and maintain good quality passivating contacts. Based on the bi-layer structure, we fabricated industrial-sized tunnel oxide passivated contact (TOPCon) solar cells, which attained an average efficiency of 23.84%. Our work not only presents a promising strategy for improving the performance of passivating contacts via the PECVD approach but also underscores the significant potential for its widespread implementation in industrial TOPCon solar cell manufacturing.

Field‐representative evaluation of PID‐polarization in TOPCon PV modules by accelerated stress testing

AbstractPotential‐induced degradation‐polarization (PID‐p) can reduce module power, but how to project the extent to which PID‐p may occur in field conditions considering the factors of system voltage, condensed moisture, temperature, and illumination has not been clarified. Using tunnel oxide passivated contact (TOPCon) modules, this work demonstrates a method to test full‐size crystalline silicon PV modules for PID‐p to provide field‐representative results. In initial screening tests with positive or negative 1000 V electrical bias applied at 60°C for 96 h using Al foil electrodes on the glass surfaces, the module type exhibited reversible PID‐p only on the front face when the cell circuit was in negative voltage potential. No PID was detected on the rear after testing in either polarity. We then evaluated the PID‐p sensitivity on the front side under different UV irradiances while maintaining the glass surface wet to estimate real‐world susceptibility to PID‐p. The magnitude of the observed behavior was fit using a previously developed charge transfer and depletion by light model. Whereas power loss with −1000 V applied to the cell circuit at 60°C for 96 h in the dark was about 30%, testing the module front under 0.051 W·m−2 nm−1 at 340 nm UVA irradiation using fluorescent tubes, the mean degradation was only 3%. When the modules were tested in the dark for PID‐p with in situ dark current–voltage (I‐V) characterization, the thermal activation energy for degradation was 0.71 eV; for recovery in the dark, it was 0.58 eV. Whereas recovery from the degraded state at 60°C in the dark without voltage bias was 5% absolute in 38 h, rapid recovery of about 5% absolute was observed with 1000 W·s/m2 exposure at 25°C using a flash tester.

Data-Driven Tunnel Oxide Passivated Contact Solar Cell Performance Analysis Using Machine Learning.

Tunnel oxide passivated contacts (TOPCon) have gained interest as a way to increase the energy conversion efficiency of silicon solar cells, and the International Technology Roadmap of Photovoltaics forecasts TOPCon to become an important technology despite a few remaining challenges. To review the recent development of TOPCon cells, this work has compiled a dataset of all device data found in current literature, which sums up to 405 devices from 131 papers. This may seem like a surprisingly small number of cells given the recent interest in the TOPCon architecture, but it illustrates a problem of data dissemination in the field. Notwithstanding the limited number of cells, there is a great diversity in cell manufacturing procedures, and this work observes a gradual increase in performance indicating that the field has not yet converged on a set of best practices. By analyzing the data using statistical methods and machine learning (ML) algorithms, this work is able to reinforces some commonly held hypotheses related to the performance differences between different device architectures. This work also identifies a few more unintuitive feature combinations that would be of interest for further experimentally studies. This work also aims to inspire improvements in data management and dissemination within the TOPCon community.

Blistering-free carbon-doped polysilicon (n+) passivating contact with high surface passivation properties prepared by industrial tube PECVD

Tube plasma-enhanced chemical vapor deposition (PECVD) has garnered attention as a promising large-scale production tool for in-situ doped polysilicon due to its high capacity and low equipment cost. In this work, we explore the use of carbon (C)-doped a-Si:H (n+), deposited by tube PECVD, for tunnel oxide passivated contact (TOPCon) solar cells. By introducing carbon atoms into polysilicon, blistering-free polysilicon films with excellent passivation properties can be obtained. The optimized sample with C-doped polysilicon (n+) exhibits remarkable surface passivation with a single-sided saturation current density (J0,s) of 1.25 fA/cm2, an implied open-circuit voltage (iVoc) of 751 mV, and a corresponding effective lifetime exceeding 18 ms at a minority carrier concentration of 1 × 1015 cm−3. UV Raman measurements reveal that C doping suppresses the crystallization of polysilicon, leading to a significant stress in the film. Despite excessive C doping, the contact resistivity extracted from the TLM method remains below 13.6 mΩ cm2. As a result, a champion conversion efficiency of 23.64 % was achieved in a small-sized proof-of-concept n-type TOPCon solar cell. This demonstrates the feasibility of fabricating C-doped polysilicon (n+) prepared by tube PECVD for high-efficiency and low-cost TOPCon solar cells.

Theoretical analysis of backside polycrystalline silicon layer in the TOPCon solar cells

As an upgraded version of passivated emitter and rear cell (PERC) solar cells, the performance of tunnel oxide passivating contacts (TOPCon) solar cells is very dependent on the silicon oxide layer and poly-Si layer. We found that different crystallization rates or doping of germanium, carbon and other elements in poly-Si can change the band gap of poly-Si, which has an impact on the efficiency (Eff) of TOPCon solar cells. Therefore, the appropriate band gap is particularly important. At the same time, the internal defect of poly-Si also have great influence on the performance of solar cells. The simulated band diagram, charge carrier concentration and recombination rate were used to deeply explore the defect in poly-Si and the influence of poly-Si with different band gap on the performance of TOPCon solar cells.

Accelerated damp-heat testing at the cell-level of bifacial silicon HJT, PERC and TOPCon solar cells using sodium chloride

Bifacial passivated emitter and rear cells (PERC) currently have the highest share in the photovoltaic market. However, heterojunction (HJT) and tunnel oxide passivated contact (TOPCon) solar cells are expected to gain significant market share shortly. Despite technological advancements, concerns about the reliability of HJT and TOPCon technologies when deployed in the field still need to be addressed. This work investigates the impact of sodium chloride (NaCl) on damp-heat-induced degradation in bifacial HJT, PERC, and TOPCon solar cells by exposing the solar cells to NaCl before damp heat (DH) testing. It is found that among all investigated cell technologies, TOPCon solar cells degrade the most with maximum power (Pmax) loss of up to ∼75%rel, followed by HJT (Pmax drops ∼50%rel), and PERC cells (Pmax drops only ∼10%rel) after 20 h of DH testing, mainly attributed to an increase in Rs on the front side of TOPCon cells, both sides of HJT cells and the rear side of PERC cells. The front of the PERC and the rear of the TOPCon solar cell are found to be stable. The rise in Rs is attributed to the corrosion of the metal contact, which is caused by a high amount of Na+ and Cl− ions penetrating the metal contact. This corrosion leads to increased porosity, detachment of the contact from the silicon interface, and increased recombination loss in some cases. These results are crucial for all cell technologies as they highlight the potential failures that could occur in the field. Na+ and/or Cl− ions are common contaminants present in solar glass, human fingerprints, soldering flux, rainwater, soil/dust, and seawater. During field operation, these ions have the potential to penetrate and directly interact with solar cells. In our view, the preferred solution is for the solar cells to be corrosion-resistant, which can be rapidly assessed using the method presented in this work.

Application of dual-layer polysilicon deposited by PECVD in n-type TOPCon solar cells

Plasma-enhanced chemical vapor deposition (PECVD) has attracted much attention in the current mass-production of n-type tunnel oxide passivated contact (TOPCon) crystalline silicon (c-Si) solar cells because of the advantages of fast film forming rate and compatibility with in-situ doping. However, the PECVD technology is limited by the effect of ion bombardment on the ultra-thin SiO2 layer during gas ionization, together with the inevitable front wrap-around poly-Si. Here, the dual-layer poly-Si stack made up of the intrinsic poly-Si(i) and in-situ P-doped poly-Si(n+) has been achieved by adjusting the deposition power, pulse voltage duty cycle, and flow rate of the PH3, which effectively protects the tunneling SiO2 layer through the weakened ion bombardment to improve the interface passivation and contact resistivity. We have demonstrated that the pinhole density is an important reason for the thinner SiO2 layer optimized less than 1.0 nm. More importantly, the conversion efficiency of n-type TOPCon c-Si solar cells can be improved by more than 0.10% and 0.15%, respectively, by the combination of the dual-layer poly-Si stack and wrap-around poly-Si removal compared with the single-layer poly-Si counterpart with the same thickness.

TOPerc Solar Cell: An Integral Approach of Tunnel Oxide Passivated Contact (TOPCon) and Passivated Emitter and Rear Contact (PERC) Architectures for Achieving Efficiency Beyond 25%

Passivated emitter and rear contact (PERC) on p‐type mono silicon has a roadmap for achieving >24% efficiency. The decrease of the full‐area rear metal contact to partial rear contact (<10%) accounts for the majority of the increase in efficiency of PERC solar cells over Al‐BSF solar cellswhich reached its maximum efficiency around 19.5%. P‐type tunnel oxide passivated contacts (TOPCon) solar cells have achieved further improvement in efficiency ≥25% by completely removing the partial rear metal contact and introducing a thin tunneling oxide layer at the rear. Thus passivating the partial rear and front metal contacts using SiOx/poly‐Si tunnelling layer stacks and an AlOx/SiNx stack on the entire back surface to passivate the remaining areas might lead to further advancements in PERC solar cells. Therefore, by integrating TOPCon and PERC architectures, as originally proposed by Fraunhofer lab, a modified design known as TOPerc solar cell has been studied in depth in this paper. Using 3D Sentaurus TCAD simulation software, a thorough numerical simulation of a p‐TOPerc solar cell has been performed. It is shown that efficiency of 25.2% and 26.0% is obtained for a p‐type wafer of bulk lifetime of 400 μs and 5.0 ms, respectively.

24.18% efficiency TOPCon solar cells enabled by super hydrophilic carbon-doped polysilicon films combined with plated metal fingers

Electroplating technology which has the potential of reducing silver consumption and lowering fabrication costs has been widely used in the photovoltaic (PV) devices. However, the poor wettability of the polysilicon film limits the application of the electroplating technology on tunnel oxide passivated contact (TOPCon) solar cells (SCs). In this work, we propose a carbon (C)-doped polysilicon with highly polar C–Si bonds to improve the surface wettability of polysilicon film. By reducing the hydrogen bubble retention during plating, a uniform, dense, and void-free Ni seed layer can be obtained. To maintain the good conductivity of polysilicon, a double-layer polysilicon structure consisting of a C-doped and a C-free polysilicon films was constructed for TOPCon device fabrication. The new design shows an excellent passivation quality with an implied open-circuit voltage (iVoc) of 745 mV for the lifetime sample and a good contact performance with a low contact resistivity (ρc) of 2–3 mΩ cm2 between plated grids and polysilicon films. Finally, the proof-of-concept TOPCon devices with the double-layer polysilicon structure and plated metal electrodes deliver a remarkable power conversion efficiency (PCE) of 24.18%. Therefore, the C-doped polysilicon combined with the electroplating technology demonstrated in this work shows great potential to obtain high-efficiency and low-cost TOPCon SCs in the PV industry.

Thermal laser separation and high-throughput layer deposition for edge passivation for TOPCon shingle solar cells

This work demonstrates the reduction of cutting-induced losses on tunnel-oxide passivated contact (TOPCon) shingle solar cells via edge passivation using high-throughput layer deposition. TOPCon shingle solar cells with a size of 26.46 mm × 158.75 mm are separated from industrial full-square TOPCon host cells either by laser scribing and mechanical cleaving (LSMC) from the emitter-free rear side or by thermal laser separation (TLS) from the front side. TLS yields up to 0.2%abs more efficient shingle cells directly after singulation in comparison to shingle cells that have been separated by LSMC. Passivated edge technology (PET) is applied by depositing aluminum oxide (Al2O3) layers using two different tools: thermal atomic layer deposition (T-ALD) in a lab-scale tool with a throughput of tens of shingle cells per hour and a high-throughput plasma-enhanced ALD (PE-ALD) prototype tool with a throughput of about 60,000 shingle cells per hour. The energy conversion efficiency of the edge-passivated shingle cells after T-ALD Al2O3 PET is found to be 0.4%abs higher than directly after separation. This gain is the same regardless of whether LSMC or TLS is used for cell separation. For PE-ALD Al2O3 and TLS, a gain of 0.5%abs is measured after PET. Stringing tests with electrically conductive adhesive so far indicate that Al2O3 layers do not negatively affect the resistance of cell to cell interconnections. Thus, low-damage cell cutting in combination with high-throughput Al2O3 layer deposition for edge passivation is a very promising approach to maintain high efficiency for industrial TOPCon solar cells in shingled modules.

24.7% industrial tunnel oxide passivated contact solar cells prepared through tube PECVD integrating with plasma-assisted oxygen oxidation and in-situ doped polysilicon

Tunnel oxide passivated contact (TOPCon) solar cells have gradually dominated the industrial silicon solar cells. In this paper, we have adopted the tube plasma-enhanced chemical vapor deposition (PECVD) technology integrating with nano SiOx (Tox) and in-situ phosphorus-doped polysilicon (n + poly-Si), in which Tox is prepared by plasma-assisted oxygen (O2) oxidation. Passivation and contact performance of TOPCon solar cells have been investigated under different thicknesses of Tox, and the following simulation has confirmed the optimal electrical properties, i.e., the implied open-circuit voltage (iVOC) of the hydrogenated lifetime sample is promoted to more than 736.1 mV on the textured wafer, corresponding to a lowest single-sided saturation current density (J0) of 4.6 fA/cm2, and the contact resistivity of 1.55 mΩ cm2 extracted from the transmission line method. Characterizations are carried out to conform the rear stack passivation layers satisfy the requirement of the high-efficiency TOPCon solar cells. Finally, we have fabricated the large-sized TOPCon solar cells with an average efficiency of 24.5% and a maximum efficiency of 24.7%, respectively. The above work has demonstrated the tube PECVD technology integrating with plasma-assisted O2 oxidation and in-situ doped poly-Si has the potential for the mass-production TOPCon in industry.

Enhancing poly-Si contact through a highly conductive and ultra-thin TiN layer for high-efficiency passivating contact silicon solar cells

High-performance passivating contacts with excellent electron selective property is a prerequisite for silicon solar cells with high power conversion efficiency. In this work, a highly conductive, ultra-thin electron-selective titanium nitride (TiN) film is prepared by reactive magnetron sputtering for tunnel oxide passivated contact (TOPCon) solar cells. The deposition parameters, crystal structure, and chemical state were systematically investigated. A higher TiN content and stronger TiN (111) diffraction peak resulted in higher conductivity. We demonstrated that the TiN film possessed a conductivity as high as 5000 S/cm and a relatively low work function of 4.26 eV. An ultra-thin TiN film (1–2 nm) was inserted between the n+ poly-Si and rear electrode to reduce the interface contact resistance and interface barrier height and subsequently obtain better electron transport. The cross-sectional morphology and elemental distribution of the n+ poly-Si/TiN/Ag interface were tested using high-resolution transmission electron microscopy. The developed TiN film was a proof of concept, and it demonstrated an impressive cell efficiency of 24.6% (Voc = 707.1 mV, Jsc = 41.62 mA/cm2, FF = 83.7%) on TOPCon solar cells. Our work provides vital insights and a detailed supplement toward the optimization of electron contact for silicon solar cells or perovskite solar cells. The outcomes of the study indicate the potential for use in applications involving high fill factor photovoltaic devices.