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A P‐doped polycrystalline silicon‐nitride (n‐poly‐SiNx) as the electron selective collection layer in a tunnel oxide passivated contact (TOPCon) solar cell is reported. The nitrogen content is controlled by the active gas ratio of R = NH3/(SiH4 + NH3) during the plasma‐enhanced chemical vapor deposition (PECVD) process. The effects of R ratio on the material's composition, crystallinity, surface passivation, and contact resistivity are investigated. The poly‐SiNx contact exhibits improved surface passivation in comparison with the reference poly‐Si without N incorporation. The best double‐sided passivated n‐type alkaline‐polished crystalline silicon wafer with the n‐poly‐SiNx/SiOx manifests the highest implied open‐circuit voltage (iVoc) of ≈745 mV, with the corresponding single‐sided saturated current density of 1.7 fA cm−2 and the effective lifetime (τeff) of 10 ms at the injection level of ≈1 × 1015 cm−3. In contrast, the controlled sample with an n‐poly‐Si/SiOx passivation contact has a maximal iVoc of 738 mV. However, the primary drawback of the N doping is to raise the contact resistivity, but which is still in an acceptable range and shows little effect on the performance of solar cell with full‐area contact. The proof‐of‐concept TOPCon solar cell using the n‐poly‐SiNx/SiOx passivating contact has achieved an efficiency of 23.88%, indicating the potential of the n‐poly‐SiNx for high‐efficiency TOPCon solar cells. [ABSTRACT FROM AUTHOR]

Metallization of high‐efficiency n‐type solar cells with tunnel oxide passivated contact (TOPCon) structures often requires a high‐temperature rapid‐thermal‐annealing (RTA) process, which potentially induces a notable degradation of device performance. Herein, the RTA‐induced passivation degradation mechanisms and potential recovery processes are clarified by postthermal annealing or hydrogenation based on both Czochralski (Cz) silicon and cast‐multicrystalline (cast‐mc) silicon wafers. It is found that the RTA process induces at least two kinds of defects, i.e., thermal‐quenching‐induced defects and hydrogen‐release‐induced defects. The passivation quality can be partially recovered under a high‐temperature annealing at 820 °C, which, however, can be fully restored via a postmoisture/nitrogen hydrogenation treatment at 450 °C. In general, the two mentioned wafers, i.e., n‐type Cz c‐Si and cast‐mc silicon substrates, demonstrate similar passivation behaviors in most cases before and after RTA treatment. Finally, it is inferred that the inferior passivation properties of the n‐type cast‐mc silicon samples are related to the relatively low bulk quality. This can be confirmed by the fact that samples with n‐type cast‐mc Si substrates show an abnormal passivation behavior with highly effective lifetimes in the low‐density carrier region, suggesting the existence of electron trapping states. [ABSTRACT FROM AUTHOR]

The concept of passivating contacts is indispensable for realizing high-efficiency crystalline silicon (c-Si)-based solar cells, and its implementation and integration into production lines has become an essential research subject. A desirable transparent passivating contact should theoretically combine excellent electrical conductivity, distinguished surface passivation and high optical transparency. However, it is challenging to simultaneously achieve the optimization of all three requirements. Here, the application potential of the phosphorous-doped polycrystalline silicon-oxide (n-poly-SiO x) as an efficient hole-selective contact in tunnel oxide passivated contact (TOPCon) solar cells is highlighted. The oxygen content can be regulated by the carbon dioxide (CO 2) gas flow during the plasma enhanced chemical vapor deposition (PECVD) process, and the optimal doping concentration is determined. While the wide band gap of n-poly-SiO x enables ideal optical performance, it also ensures excellent passivation and high conductivity, which eventually translates into an optimized short-circuit current density (41.53 mA/cm2), fill factor (79.21%), open-circuit voltage (687.8 mV) and efficiency of 22.62% for the proof-of-concept TOPCon solar cell. Additionally, this contact with the incorporation of oxygen elements can suppress the formation of hydrogen-induced blisters, which critically degrades passivation. Our work highlights a promising strategy to improve the performance of TOPCon solar cells by employing n-poly-SiO x based transparent passivating contact, and its passivation mechanism and working principle are also investigated. [Display omitted] • The application potential of the n-poly-SiO x as an efficient hole-selective contact in TOPCon solar cells is highlighted. • The wide band gap of n-poly-SiOx enables ideal optical property, it also ensures excellent passivation and conductivity. • The contact with the incorporation of oxygen element can suppress the formation of hydrogen-induced blisters. • An efficiency of 22.62% for the cell employing n-poly-SiOx based transparent passivating contact is obtained. [ABSTRACT FROM AUTHOR]

• The double-sided p-TOPCon passivated lifetime samples with p-type Si substrates achieve a high implied open-circuit voltage of ∼ 734 mV and a low single-sided saturation current density of ∼ 4.5 fA/cm2. • The contact resistivity is below 5 mΩ‧cm2, yielding a remarkable selectivity of 15.6. • The precursor cell manifests an excellent iV oc of 717 mV. • The proof-of-concept p-TOPCon solar cells exhibit a remarkable efficiency of 22.23%. High-quality p-type tunnel oxide passivated contact (p-type TOPCon) is a feasible technical solution to further improve the efficiency of TOPCon silicon solar cells. Plasma-enhanced chemical vapor deposition (PECVD) technology route could deposit boron-doped amorphous silicon film in-situ and thus becomes one of the most promising industry routes to prepare the TOPCon structure. However, the passivation quality of p-type TOPCon by PECVD is not satisfactory till now. In this work, we develop the high-performance p-type TOPCon technology by integrating the ozone-gas oxidation to prepare the ultra-thin SiO x film, which shows excellent passivation and contact properties. The experimental results suggest that the double-sided p-type TOPCon passivated samples with p-type Si substrates receive a maximal implied open-circuit voltage (iV oc) of ∼ 734 mV together with a minimum single-sided saturation current density (J 0,s) of ∼ 4.5 fA/cm2. Correspondingly, the contact resistivity is less than 5 mΩ·cm2, yielding a high selectivity S 10 of 15.6, which is one of the best values for p-type TOPCon technology. As a result, the precursor cell manifests an excellent iV oc of 717 mV, and the p-type silicon solar cell with rear-sided p-type TOPCon passivating contact receives a high efficiency of 22.23%. Generally, this work provides a promising technology for preparing the high-quality p-type TOPCon passivating contact for industrial application. [ABSTRACT FROM AUTHOR]

• Two-step oxidation (TSO) was effective in suppressing the ion-bombardment damage. • PECVD p-TOPCon with TSO SiO x shows excellent passivation with an iV oc of ∼712 mV and a J 0,s of ∼10 fA/cm2. • P-TOPCon with TSO SiO x produces a low contact resistivity of ∼10 mΩ·cm2. • An efficiency of 24.6% based on the state-of-the-art technology is predicted by numerical simulations. Tunnel oxide passivated contact (TOPCon) integrated with a plasma-enhanced chemical vapor deposition (PECVD) boron-doped polysilicon has the potential to achieve high-efficiency and low-cost solar cells. In this contribution, we explore the feasibility of using PECVD technology to prepare high-performance p-type TOPCon (p-TOPCon) by growing two-step oxidation (TSO), i.e., a nitric acid oxidation (NAOS) SiO x without ion-bombardment followed by a plasma-assist N 2 O oxidation (PANO) SiO x layer. The experimental results reveal that for p-TOPCon structures on polished wafers with the conventional plasma oxidation SiO x , raising plasma oxidation powers to increase the thickness and oxidation degree of SiO x cannot ensure high-quality passivation due to the appearance of high-density defects caused by plasma ion-bombardment. In the presence of an additional NAOS SiO x layer, ion-bombardment-induced defects can be effectively suppressed, leading to a remarkable improvement in passivation properties. In detail, the optimal p-TOPCon with TSO SiO x achieves a maximum implied open-circuit voltage (iV oc) of ∼712 mV and a minimum single-sided saturation current density (J 0,s) of ∼10 fA/cm2, manifesting an increment of iV oc by ∼10 mV, and a reduction of J 0,s by ∼5 fA/cm2. Finally, the numerical simulations reveal that n-type Si solar cells featuring p-TOPCon rear junction and Al electrode could receive an efficiency of 24.6% based on the state-of-the-art device fabrication technology. In general, this work provides a new way to boost the passivation quality of PECVD p-TOPCon devices. [ABSTRACT FROM AUTHOR]

• a-Si:H deposited by PECVD exhibits excellent passivation quality for p-mc-b-Si. • Excellent passivation quality with an iV oc of up to 710 mV is achieved. • a-Si:H passivates surface defects and bulk trap defects of p-mc-b-Si effectively. • a-Si:H/SiN x helps p-mc-b-Si to achieve excellent passivation with low reflectance. Hydrogenated amorphous silicon (a-Si:H) deposited using plasma-enhanced chemical vapor deposition (PECVD) is used as the passivation layer for p-type multi-crystalline black silicon (p-mc-b-Si) wafers. The effects of deposition conditions on passivation quality are investigated. The optimized a-Si:H passivation layer enables the best surface passivation with an implied open-circuit voltage (iV oc) of 710 mV, which is better than other conventional passivation materials. The excellent passivation quality possibly resulted from that the activated hydrogen from a-Si:H at ~200 °C was able to passivate both surface defect states and bulk trap states of p-mc-b-Si effectively. Moreover, an additional SiN x capping layer helps to reduce reflectance significantly and to keep passivation quality. This work suggests that b-Si passivated by a-Si:H/SiN x stack film shows potential for various optoelectronic devices that requires both excellent optical anti-reflectance and surface passivation. [ABSTRACT FROM AUTHOR]

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 (J 0,s) of 1.25 fA/cm2, an implied open-circuit voltage (iV oc) 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. [ABSTRACT FROM AUTHOR]

We study the preparation of high-quality p-type tunnel oxide passivated contact (p-TOPCon) using plasma-enhanced chemical vapor deposition (PECVD) technology in this work. We propose to use different plasmas to treat the ultrathin SiO x to improve the passivation quality of p-TOPCon. Experimentally, we use the nitric acid oxidation (NAOS) SiO x as the precursor and use pure N 2 , pure H 2 , and N 2 O/H 2 plasmas to treat the SiO x precursor layer. Three observations are found. 1) Pure H 2 plasma treatment can improve the SiO x quality by increasing the Si4+ content, but the passivation quality is not improved because of the etching effect of H 2 plasma and the reduction of SiO x thickness. 2) The pure N 2 O plasma can improve the passivation quality but increases the contact resistivity (ρ c) because of the increase of the SiO x thickness. 3) The N 2 O/H 2 plasma treatment improves the passivation quality more effectively than pure N 2 O plasma, and meanwhile, it also keeps the contact resistivity at an acceptable value for high-efficiency solar cells. We assume that the atomic H provides the energy to etch the weak and dangling bonds and make SiO x thinner, while the atomic O that makes SiO x thickness unchanged balances the etching effect of atomic H. With the optimized N 2 O/H 2 plasma treatment, the passivation quality of p-TOPCon is improved, featuring the best implied open-circuit voltage (iV oc) of ∼732 mV and the lowest single-sided saturation current density (J 0,s) of ∼6 fA/cm2 on the lifetime sample with the n-type silicon substrate and the AlO x /SiN x capping layer. These results demonstrate that the plasma treatment is a promising way to boost the passivation quality of PECVD p-TOPCon structures. Finally, as an example, we use numerical simulation to predict the performances of the solar cells integrating the p-TOPCon structure on the rear side of n- c -Si and demonstrate a 24.8% efficiency with the p-TOPCon whose SiO x is improved by the optimized plasma treatment. • Pure H 2 plasma treatment increases Si4+ content of SiO x but decreases SiO x thickness. • Pure N 2 O plasma treatment increases SiO x thickness significantly. • N 2 O/H 2 plasma treatment increases Si4+ content of SiO x and enhances SiO x thickness. • N 2 O/H 2 plasma treatment balances passivation and contact resistivity of p-TOPCon. • N 2 O/H 2 plasma treatment leads to best passivation with iV oc of ∼732 mV and J 0,s of ∼6 fA/cm2. [ABSTRACT FROM AUTHOR]

We investigate the effects of plasma-enhanced chemical vapor deposition (PECVD) preparation conditions and microstructures of the boron-doped polysilicon films on the passivation quality of p-type tunnel oxide passivated contact (p -TOPCon) integrated with plasma-assisted N 2 O oxidation (PANO) SiO x. The B 2 H 6 gas flow, activation temperature, substrate temperature, H 2 dilution ratio, and carbon (C)-doped polycrystalline silicon insertion layer are investigated. The best passivation based on plane-surface n-type CZ-Si lifetime sample manifests an implied open-circuit voltage (iV oc) of 706 mV, a single-sided saturation current density (J 0,s) of 17.9 fA/cm2, and an effective lifetime (τ eff) of 2.25 ms at 1 × 1015 cm−3, showing a slight improvement compared with the controlled sample featuring an iV oc of 703 mV. Although this passivation quality is one of the best specifications of the p -TOPCon featuring PANO SiO x so far, it is insufficient for industry application. Detailed experimental studies and a numerical simulation suggest that the passivation quality is probably weakened by the boron-induced defects located at the interfacial and beneath the SiO x , whose harmful influence is difficult to offset by the field-passivating effect. Generally, we provide new insight into the bottleneck of the p -TOPCon's passivation and then discuss the new strategies for improving the p -TOPCon's passivation in this paper. [ABSTRACT FROM AUTHOR]

Ozone-gas oxidation (OGO) technology, capable of integrating into tube plasma-enhanced chemical vapor deposition (PECVD) technology, is developed to prepare the Nano SiO x layer for tunnel oxide passivated contact (TOPCon) solar cells in this work. The effects of gas flow, oxidation temperature, and annealing temperature on passivation quality are investigated. The X-ray photoelectron spectroscopy (XPS) indicates that OGO SiO x possesses a Si4+ proportion of about 20%, higher than the nitric acid oxidized (NAOS) SiO x and plasma-assisted N 2 O oxidation (PANO) SiO x. The implied open-circuit voltage (iV oc) of the hydrogenated lifetime sample is promoted to more than 740 mV with the highest value of 748 mV, corresponding to a lowest single-sided saturation current density (J 0,s) of 3.1 fA/cm2. The contact resistivity extracted from the Cox-Strack method is < 9 mΩ cm2 as the annealing temperature is more than 840 °C. Finally, we prepared the large-sized TOPCon solar cells with an average efficiency of 24.37% and a maximum efficiency of 24.41%, respectively. The above work shows that the tube PECVD technology integrated with ozone gas oxidation has the potential for the mass-production TOPCon industry. • Ozone-gas oxidation (OGO) technology is integrated into tube PECVD technology. • OGO SiO x and P-doped a-Si:H can be prepared by the same graphite-boat carrier. • OGO SiO x shows a high proportion of Si4+ without ion bombardment. • The highest iV oc of 748 mV corresponding to the lowest J 0,s of 3.1 fA/cm2. • Average efficiency of 158.75 mm TOPCon cells reaches ∼24.4%. [ABSTRACT FROM AUTHOR]

We present a systematic study of emitter formation with dopant diffusion from boron (B)-doped hydrogenated silicon oxide (a-SiO x :H) deposited on textured n-type monocrystalline silicon (n-c-Si) wafers using a 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) system. The B atoms in the a-SiO x :H are activated and diffused into the n-c-Si wafer during a high-temperature annealing to form a p/n junction for solar cell application. Afterward, the B-doped SiO x layer is removed by hydrofluoric acid selective etching to obtain a clean surface for the deposition of AlO x passivation and SiN x antireflection layers. With the optimization of the PECVD deposition and the following annealing/etching processes, the B diffused region with a sheet resistance of 60–100 Ω/sq and a junction depth of 1.2–1.5 μm is obtained. A champion implied open-circuit voltage (iV oc) of 705 mV and a single-side saturated recombination current density (J 0,s) of 17.6 fA/cm2 are obtained from a double-sided B diffused sample after the passivation with an atomic-layer-deposition (ALD) AlOx. In addition, the contact resistivity (ρ c) at the metal/emitter interface is lower than 5 mΩcm2, where the metal contact is a Ti/Pd/Ag tri-layer structure. All of the material properties meet the requirements of high-efficiency solar cell. With the optimized emitter in the front, we made a SiO x and heavily phosphorus-doped polycrystalline silicon carbide (n-poly-SiC x) stack on the rear surface to form tunnel oxide passivated contact (TOPCon) solar cells. The results show that the iV oc of semi-finished TOPCon solar cell before metallization is more than 725 mV. Finally, a TOPCon solar cell with an efficiency of 24.24% is obtained, which is comparable with the TOPCon solar cells with the industrial thermally diffused emitter. • Boron doped emitter is formed by thermal annealing of PECVD deposited boron doped a-SiOx:H. • The PECVD based emitter has a similar dopant profile as the thermally diffused emitter in an industrial TOPCon solar cell. • The PECVD based emitter has a great passivation of iV oc = 705 mV and low contact resistivity <5 mΩcm2. • The TOPCon solar cell with the PECVD based emitter shows an efficiency of 24.24%. [ABSTRACT FROM AUTHOR]

A rapid thermal anneal (RTA) is used to crystallize the plasma-enhanced chemical vapor deposition (PECVD) deposited hydrogenated amorphous silicon (a-Si:H) thin film to form the phosphorus-doped polysilicon passivated contact in tunnel oxide passivated contact (TOPCon) solar cells. The effects of annealing temperature, annealing time, cooling time, and the polysilicon thickness on the surface passivation are investigated. The primary advantage of the RTA is reducing the whole crystallization period to ~15 min, shorter than the conventional tube-furnace annealing period of >60 min. We find that the RTA is a robust method to prepare high-quality polysilicon passivated contact without introducing blistering when the thickness of the a-Si:H is less than 40 nm. The optimized RTA process leads to an implied open-circuit voltage (i V oc) of 712 mV and a single-sided dark saturation current density (J 0,s) of 12.5 fA/cm2 in the as-annealed state, which is inferior to the surface passivation of the controlled one prepared by a tube furnace annealing. Fortunately, a subsequent Al 2 O 3 capping hydrogenation improves the i V oc and J 0,s to 727 mV and 4.7 fA/cm2, respectively. The champion conversion efficiency of 23.04% (V oc = 679.0 mV, J sc = 41.97 mA/cm2 and FF = 80.86%) is achieved, which demonstrates the effectiveness of RTA for preparing a high-efficiency polysilicon passivated-contact solar cell. • N-type polysilicon passivated contact structure annealed by Rapid-Thermal Anneal (RTA) is studied. • The effects of the annealing temperature, annealing time, cooling time, polysilicon thickness on surface passivation are investigated. • The whole crystallization period of RTA is reduced to ~15 min with the best i V oc of 727 mV and J 0,s of 4.7 fA/cm2 after hydrogenation. • Limiting polysilicon thickness to less than 40 nm helps to avoid blistering. • The polysilicon passivated-contact solar cell prepared using RTA shows a champion conversion efficiency of 23.04%. [ABSTRACT FROM AUTHOR]

We report an industrial compatible tunnel oxide passivated contact (TOPCon) structure on solar-grade p-type c-Si wafer as the rear emitter for high-efficiency solar cells, where the ultrathin silicon oxide (SiO x) is made by plasma-assisted oxidation and the P-doped n-type poly-Si (n+-poly-Si) contact layer by plasma-enhanced chemical vapor deposition (PECVD) of hydrogenated amorphous silicon (a-Si:H) with in-situ doping with PH 3 and following the high-temperature annealing. The fabrication processes of SiO x and n+-poly-Si layers are systematically optimized. It is found that the optimized annealing temperature for the crystallization and dopant activation is in the range of 850 °C and 880 °C, which is higher than the similar structure with chemically oxidized SiO x (820 °C). In addition, the samples made with higher PH 3 /SiH 4 doping ratio during the a-Si:H deposition need a lower annealing temperature to reach the similar dopant distribution within the samples made with lower doping ratio but annealed at higher temperature, it means that the optimized annealing temperature decreases with the increase of the PH 3 /SiH 4 doping ratio during the deposition of a-Si:H precursor. The optimized process with post-hydrogenation yields excellent surface passivation on the p-type Si substrate with the implied open-circuit voltage (i V oc) of ∼742 mV, the single-side saturated recombination current density (J 0) of ∼3.0 fA/cm2, the contact resistivity (ρ c) of ∼2–4 mΩ cm2, and the effective minority carrier lifetime (τ eff) of ∼1050 μs (Δn = 1 × 1015 cm-3). With these passivation parameters, a simulation study demonstrates the advantage of rear emitter over the conventional front emitter TOPCon solar cell with ∼22.8% achievable efficiency on solar-grade p-type wafers with current industrial constraints, and ∼24.9% on high quality p-type c-Si wafers with the optimized conditions in R&D laboratories. Our study suggests that the p-type c-Si solar cell with a rear n+-poly-Si TOPCon emitter is a viable structure for high-efficiency solar cell production. • High-quality tunnel SiO x is prepared by plasma-assisted N 2 O oxidation. • Surface passivation depends on PH 3 flow and crystallization temperature. • Excellent surface passivation on p-type substrate is achieved with i V oc = 742 mV, J 0 = 3.0 fA/cm2, τ = 1050 μs? • >22.8% n-type TOPCon rear-emitter solar cell with p-type substrate is viable for industrial manufacture. [ABSTRACT FROM AUTHOR]