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Abstract A precise characterization of thin film silicon in devices is a great challenge for device optimization because the material properties depend on the substrate and change with film thickness. A specific situation is thin poly-Si layer in tunnel oxide passivated contact (TOPCon) structure in high-efficiency solar cells. In this paper, we present a systematic study using a wide range UV-Raman spectroscopy to measure the crystalline structure and chemical bonding configurations in the TOPCon structure. Because of the high absorption coefficient of 325-nm laser in silicon films, the Raman probes only the top surface region and minimizes the contribution from c-Si substrate. However, the comparison with the Raman spectra collected with a green laser of 532 nm, the UV-Raman spectrum of a-Si:H shows a very different spectral shape with the disappearance of the LA mode of Si-Si vibration and an appearance of additional signal at 325 cm−1. In addition, the UV-Raman spectrum of the pre-crystallized P doped a-Si:H layer shows most of the vibration modes of Si–Si, Si–H, Si–O–Si and Si–O–H bonds, where the Si–O–H bonds are in the top surface oxide layer. After the crystallization, the Si-Si TO mode shows a high degree of crystallization, the Si-H vibration modes disappear, and an additional Si-O-Si mode is observed which is believed from the ultrathin SiO x passivation layer. In addition, we provide a set of UV-Raman measurements on the samples made with the same layer structure but at different annealing temperatures to show the correlation between the UV-Raman spectra and the passivation quality of the TOPCon structure on the n-type c-Si wafers. These observations prove that UV-Raman spectroscopy is a useful characterization tool for high efficiency c-Si solar cells with TOPCon structure. In addition, the impacts of the material properties on the passivation quality are discussed. Highlights • UV-Raman spectra of thin Si films for TOPCon solar cells are measured in real TOPCon structures. • The TA mode disappears and a sharp peak at 325 cm−1 is observed in the UV-Raman spectra of a-Si: H. • Si-Hx wagging/rocking and stretching modes are found to be correlated to passivation quality. • Si-O and Si-O-H vibration modes are detected in real TOPCon structures with the UV-Raman spectroscopy. • Correlation between UV-Raman spectra and TOPCon passivation is observed. [ABSTRACT FROM AUTHOR]

Abstract We developed a new wet-chemical method to grow the high-quality tunnel silicon oxide (SiO x) layer by using a strong-oxidizing mixed acid, which consists of three volumes of HNO 3 (68 wt%) and one volume of H 2 SO 4 (98 wt%), named as the CNS (concentrated nitric and sulfuric) acid for short. In comparison with the HNO 3 acid, the CNS acid grows high-quality SiO x layer with the higher oxidized state at 60 °C, where the relatively low temperature avoids the significant volatilization of acid and remains the quality of acid during the extending process. The results prove that the SiO x grown in the CNS acid benefits for the surface passivation of the n-type polysilicon passivated contact structure. An average gain of implied open circuit voltage (i V oc) by 2–10 mV and a reduction of single-side surface saturated dark current (J 0) by 1–7 fA/cm2 are obtained by using the 60 °C CNS-acid grown SiO x to replace the 60 °C HNO 3 -acid grown one. Also, in comparison with the 90 °C HNO 3 acid, the 60 °C CNS acid exhibits improved stability and repeatability for preparing the SiO x during the extending process. The CNS-acid grown SiO x helps the polysilicon passivated contact solar cell to raise the efficiency by ~ 0.15% on average. In summary, the CNS acid has shown the potential for industrial application, which improves not only the manufacturing process but also the device performances. Highlights • Strong-oxidizing mixed acid grows high-quality SiO x but avoids significant volatilization. • SiO x grown in mixed acid has a higher proportion of Si4+ in comparison with that grown in HNO 3. • Surface passivation is improved by using mixed acid to replace HNO 3 , i.e., a gain of i V oc by 2–10 mV. • Mixed-acid grown SiO x helps to raise the device efficiency by ~ 0.15% on average. [ABSTRACT FROM AUTHOR]

The carrier transport through the silicon-oxide (SiO x ) layer in tunnel oxide passivated contact (TOPCon) c-Si solar cells has been studied experimentally and by simulation. The current intensity versus voltage (J-V) characteristics of GaIn/n-c-Si/SiO x /n + -poly-Si/Al structures shows a linear Ohmic characteristic, while a non-Ohmic behavior is observed in the samples without the n + -poly-Si contact layer. Conductive Atomic Force Microscopy (c-AFM) images reveal some current spikes on the surface of the samples, which could be related to the transport through pinholes. The simulation results show that 1) a rectification characteristic is obtained when only the tunneling mechanism is included, 2) both the reverse saturation current and the forward current increase when a small amount of transport through pinholes is introduced, and 3) finally a linear Ohmic behavior is observed when the pinhole transport component reaches a certain level. Furthermore, the simulation for whole TOPCon solar cells provides some useful results. For very thin SiO x (< 1.2 nm), the tunneling provides sufficient high tunneling probability and high efficiency TOPCon solar cells can be obtained without transport through pinholes if the passivation is ensured; while for a relatively thick SiO x (> 1.2 nm) without the transport through pinholes, the TOPCon solar cell shows a poor fill factor ( FF ) with a high series resistance ( Rs ) because the tunneling does not provide a sufficient high transport channel for carrier transport, and the introduction of a small number of transports through pinholes improves the FF and reduces the Rs , hence improves the PCE. However, a high possibility for carrier going through pinholes reduces all of the performance parameters and degrades PCE for all the cases simulated. Therefore, an optimized pinhole density and size distribution is critical engineering for solar cell performance optimization. However, the establishment of an optimized method to precisely control the pinhole formation and characterization is still on the way. [ABSTRACT FROM AUTHOR]

In this work, the tunnel oxide passivated contact (TOPCon) with a low-work-function electron-selective-collection (ESC) layer is studied using a numerical simulation method. An exhaustive comparison between the low-work-function ESC TOPCon and the heavily-doped-Si TOPCon solar cell is carried out to find out the differences between these two kinds of devices. The work function modulated ESC TOPCon with a work function of typically <3.6 eV and a low defect-density oxide layer of 1.2–1.4 nm displays an maximum implied open circuit voltage (i V oc ) of 742 mV and a superior fill factor ( FF ) of 86%, which is competitive with a regular heavily-doped-Si ESC TOPCon solar cell. Noted that a defective transition layer (DTL) between the low-work-function layer and the oxide layer is studied herein, in which enhanced recombination decays not only the surface passivation but also the carrier transport. Also, the practical problems that might impede the development of a high-efficiency low-work-function ESC TOPCon solar cell are discussed. In summary, this work presents an overall computational analysis of the low-work-function ESC layer, tunnel oxide, defective transition layer and their combined effects on device performances, which provides a pathway towards fabricating a high-efficiency low-work-function ESC TOPCon solar cell. [ABSTRACT FROM AUTHOR]

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 (iV oc) of 745 mV for the lifetime sample and a good contact performance with a low contact resistivity (ρ c) 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. • Introducing carbon atoms into the polysilicon can effectively improve film wettability. • A dense, uniform, and void-free Ni seed layer was achieved on the carbon-doped polysilicon. • TOPCon structure with the double-layer polysilicon design shows excellent passivation and contact performance. • The proof-of-concept TOPCon solar cells with the double-layer structure exhibit a remarkable efficiency of 24.18%. [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]

In this work, we used the numerical simulation method to study the tunnel oxide passivated carrier-selective contacts (TOPCon) structured solar cells, with the focus especially on the paths towards excellent surface passivation and low contact resistance. The presence of an ultra-thin silicon oxide (SiO 2 ) with high quality (typically low interface-states density, D it ≈ 1 × 10 10 cm −2 eV −1 and low pinhole density, D ph < 1 × 10 −4 ) suppresses the recombination of carriers at the rear surface. As a result, implied open circuit voltage (i V oc ) could be promoted by a value of more than 30 mV comparing with the solar cell without oxide layer, which is the primary benefit originated from TOPCon structure. Corresponding, the iV oc and recombination current density ( J oe ) could reach ∼745 mV and ∼9.5 fA/cm 2 (Δn = 5 × 10 15 cm −3 ) for the 1-Ω cm and 200-μm n-type wafer covered with high-quality oxide and n + -Si layers. In addition to passivation, a well-designed SiO 2 /n + -Si backside structure is also critical for carrier collection. The tunneling current is susceptible to oxide thickness, i.e., a 0.2-nm increase in SiO 2 thickness results in the decrease of the tunneling current by more than one magnitude under certain circumstance. Fortunately, raising the doping in n + -Si layer enhances the tunneling possibility of electron, which allows for a thicker oxide that is favorable to a stable mass production. The simulation suggests that to obtain a high fill factor ( FF , >84%), a minimum forward-bias saturated tunneling current of about 0.01 A/cm 2 , more favorable of 0.1 A/cm 2 , is required for the Si/SiO 2 /n + -Si structure. Generally, our work offers an improved understanding of tunnel oxide, doping layer and their combined effects on TOPCon solar cells. Besides simulation, we also discuss the practical manufactures of how to control the above mentioned parameters, as well as the problems needed to be solved for further work. [ABSTRACT FROM AUTHOR]

As one of the prospective crystalline silicon (c-Si) technologies, tunnel oxide passivating contact (TOPCon) solar cells have recently attracted much attention in the photovoltaic community. However, the deficit of open-circuit voltage due to the imperfect passivation performance together with the insufficient understanding of the passivation mechanism, especially for the key structures of TOPCon devices (i.e. , poly-Si/SiO x /c-Si), is a crucial factor to limit the improvement of device efficiency. To unlock the full passivation potential of this type of poly-Si/SiO x /c-Si contact, we report a systematic investigation by combining experiments and simulations. The related results can be summarized: 1) the best passivation can be obtained by optimizing SiO x quality, tailoring the in-diffusion profile, and performing hydrogenation; 2) if SiO x quality is good enough, high-level passivation can be expected even without impurity doping; 3) although the deepened in-diffusion could partially alleviate the degradation of the poor surface passivation, it would also reduce the passivation performance owing to the increased Auger recombination inherent to the high impurity doping; 4) the presence of pinholes would degrade the passivation performance, especially for the cases with the good surface passivation, a shallow in-diffusion and a low doping concentration of poly-Si, where the electric-field effect was minimized. To further confirm these conclusions, recombination distributions and the corresponding current profiles of the minority carriers were reviewed. This work clarifies the passivation mechanism of c-Si/SiO x /poly-Si contact in detail and provides effective guidance for further promoting the passivation level and the efficiencies of TOPCon devices. • An experiment and complementary simulations were designed to confirm the passivation properties of c-Si/SiO x /poly-Si contacts. • Annealing temperature, hydrogenation and SiO x quality were simultaneously regulated to promote passivation quality. • The underlying factors including poly-Si thickness and pinholes to affect the passivation performance were investigated in detail. • Passivation mechanisms were clarified by addressing recombination distributions and current profiles of the minority carriers. [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]

Polysilicon (poly-Si) passivating contacts have attracted considerable attentions in the academic community and photovoltaic industry due to their remarkable advantages of outstanding passivation quality and low contact resistivity. Plasma enhanced chemical vapor deposition (PECVD), as one of the widely adopted techniques to prepare doped poly-Si films, is usually limited by the occurrence of blistering, especially for boron-doped (B-doped) poly-Si films. In this work, we present a study of PECVD preparation of B-doped polycrystalline silicon carbide (poly-SiC x) films with a blistering-free appearance by incorporating carbon (C) and optimizing the annealing process. It demonstrates that a thick poly-Si deposited on polished c-Si substrates with a low surface roughness tends to blister, which thus leads to a poor passivation performance. Moreover, the investigation of C content and annealing condition suggests that increasing C content or lowering incipient annealing temperature is beneficial to suppress the blistering. However, the C content needs to be well controlled to balance the passivation and contact properties, because the excessive CH 4 flow during the film deposition would degrade the contact performance with a high contact resistivity (>100 mΩ cm2). Finally, the proof-of-concept devices featuring the double-sided passivating contacts (DPPCs) were fabricated with a front n-type poly-Si and rear p-type poly-SiC x , and presented an open-circuit voltage of 695 mV and an efficiency of 19.82%. The results clarify the correlation of C contents, c-Si substrate roughness and annealing process with the blistering levels and the passivation/contact properties, providing a valuable guidance for fabricating high-efficiency DPPC solar cells. • A path way to prepare blistering-free Boron-doped PECVD poly-Si films has been revealed. • A 90 nm thick PECVD prepared B-doped poly-Si film with a blistering-free appearance has been proposed. • A proof-of-concept double-sided poly-Si passivating contact solar cells with an efficiency of 19.82% has been presented. [ABSTRACT FROM AUTHOR]

The use of Ga-doped Czochralski (CZ) silicon wafers in Passivated Emitter and Rear Cells (PERC) has been confirmed to have a prominent advantage in suppressing light-induced degradation (LID), which will attract considerable attention for the application of Ga-doped wafers in more efficient photovoltaic devices. In this work, we investigate the passivation quality and address the issue of LID in Ga-doped CZ Si wafers equipped with p-type polysilicon passivating contact that consists of an ultrathin SiO x and a heavily doped polysilicon. We also present the modeling results for solar cells using this type of contact. The experiments show that samples with Ga-doped CZ Si wafers have superior anti-LID properties when compared to the samples with B-doped wafers. An excellent passivation performance with a high implied open-circuit voltage (iV oc) of 705 mV and a low single-sided saturation current density (J 0,s) of 9 fA/cm2 was achieved. Moreover, with the help of the numerical simulations, we predict that the p-type Ga-doped CZ Si solar cells with p-type polysilicon passivating contacts have the potential to achieve a high efficiency of 23.8%, an ~0.5% absolute efficiency improvement over that of PERC solar cells. The results demonstrated in this study suggest that Ga-doped CZ Si wafers combined with p-type polysilicon passivating contacts could resolve the LID issue while maintaining good passivation properties, providing a promising alternative for p-type solar cells in the photovoltaic industry. • The p-type TOPC on featuring Ga-doped CZ Si wafers achieved an excellent passivation quality with iV oc > 705 mV. • The passivation improvement sources of Ga-doped CZ Si-based structures were attributed to the suppression of B- and O-related defects. • Ga-doped TOPCon solar cells show the LID-free performance. • Simulation results show a comparable efficiency of 23.8% for Ga-doped TOPCon solar cells. [ABSTRACT FROM AUTHOR]

A comparison study of ultrathin atomic layer deposited AlO x , wet-chemically oxidized SiO x , and their combination as the tunnel layer in TOPCon structure with both B-doped and P-doped poly-Si contact layers on n-type c-Si wafers was carried out. The passivation quality with the three types of tunnel layers was examined as a function of thickness and annealing temperature. Ideally, the high density of negative fixed charge in the AlO x is expected to provide a positive benefit on the passivation quality with p-type poly-Si as the contact layer, however, it is surprisingly observed that the AlO x and AlO x /SiO x do not yield a better passivation than the SiO x. Searching for the mechanisms behind, an interesting phenomenon is observed that the AlO x , especially the AlO x /SiO x bi-layer, significantly enhances B diffusion and suppresses P diffusion. It is also found a remarkable accumulation of B in the AlO x and AlO x /SiO x region, forming a reservoir for B diffusion. Furthermore, the free carrier assistant extrinsic diffusion is an additional factor for the enhanced B and retarded P diffusions by the AlO x /SiO x. The enhanced B diffusion causes extra Auger recombination as well as recombination through B–O pair defects and degrades the p-TOPCon passivation quality; additionally, a quantity of Al diffuse into the c-Si wafer could be another potential factor degrading passivation quality, because Al forms deep-level defects and induces a significant SRH recombination. Image 1 • The passivation quality in p-TOPCon with ALD-AlO x and SiO x as the tunnel layer was studied. • The AlO x and AlO x /SiO x bi-layer do not provide a better passivation than the SiO x. • The AlO x and AlO x /SiO x bi-layer significantly enhance B diffusion and suppress P diffusion. • The B accumulation in the AlO x and AlO x /SiO x forms a reservoir for the enhanced B diffusion. • The free carrier assistant diffusion is another factor for the enhanced B diffusion by the AlO x /SiO x. [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 present a systematic study of highly boron (B)-doped poly-silicon (p+-poly-Si) and ultrathin silicon oxide (SiO x) bi-layer structure, also named as p-TOPCon, as the hole-selective passivated contact on n-type c-Si wafer, where the SiO x layer is made with three methods of hot nitric acid oxidation SiO x (NAOS-SiO x), plasma-assisted nitrous-oxide (N 2 O) gas oxidation (PANO-SiO x), and thermal oxidation (Thermal-SiO x). We demonstrate that the SiO x has a strong influence on the passivation quality. The best result is achieved using the Thermal-SiO x , while the NAOS-SiO x is slightly inferior, but better than the PANO-SiO x. The p+-poly-Si/SiO x structures with the three SiO x layers achieve the optimized passivation quality at different annealing temperatures of 820 °C for the NAOS-SiO x , 880 °C for the PANO-SiO x , and 930 °C for the Thermal-SiO x. The other potential factors affecting the passivation quality are also studied. The most important observation is that the optimized p-TOPCon structures with the three SiO x layers have a similar B diffusion profile, which penetrates into the c-Si wafer about 50 nm with B concentration decreasing to ~1 × 1018 cm−3. However, the overall p+-poly-Si/SiO x is still much poorer than n+-poly-Si/SiO x in terms the passivation quality. The comparison of the τ eff versus carrier injection intensity spectra suggests that the B–O complex is the passivation killer possibly, and the approaches to improve the p-TOPCon are searching the other elements to reduce the B–O defects. In addition, contact resistivity (ρ c) measurements show that the Thermal-SiO x leads a higher ρ c than the others, but its value is still low enough for high-efficiency solar cells. • The passivation of B-doped p-TOPCon structures on n-type c-Si was systematically studied. • Three kinds of SiOx layers made with HNO 3 , N 2 O plasma, and thermal oxidation were compared. • The best passivation quality with an i V oc of 722 mV, τ eff of 1.56 ms and J 0 of 5.95 fA/cm2 is obtained. • The p-TOPCon with the three SiO x layers achieves the best passivation at different annealing temperatures. • The optimized p-TOPCon structures with the three SiO x layers have a similar B diffusion profile. [ABSTRACT FROM AUTHOR]

We develop a plasma-assisted nitrous-oxide (N 2 O) gas oxidation (PANO) method to prepare the ultrathin silicon oxide (SiO x) for polysilicon (poly-Si) passivated contact. The effects of preparation conditions, including the substrate temperature, processing time, and plasma power, are studied. Afterwards, we integrate the PANO SiO x into the polysilicon passivated contact and optimize the passivation and contact performances. Excellent surface passivation with the n-type poly-Si and PANO SiO x on the n-type c-Si wafer is achieved by 880 °C annealing, which shows competitive passivation quality to the one with NASO SiO x. Champion implied open-circuit voltage (i V oc) and single-sided recombination saturated current (J 0) reach 730 mV and 4.3 fA/cm2 after crystallization; and they are further improved to 747 mV and 2.0 fA/cm2 (3 × 1015cm−3) after subsequent AlO x /SiN x hydrogenation. Using transmission electron microscopy (TEM), we find that the thickness of PANO SiO x ranges 1.1–2.4 nm and the controlled nitric acid oxidized SiO x (NAOS) ranges 1.3–1.8 nm. The contact resistivity (ρ c) is typically <10 mΩ cm2 with the annealing temperature of >820 °C. Also, the crystallinity, phosphorous in-diffusion profile, and current-leaking density of the passivated contacts are investigated. In general, the PANO SiO x and in-situ doping amorphous silicon precursor can be fabricated in one PECVD system without additional equipment or transfer procedures, which is favorable for the high-efficiency, low-cost industrial manufacture. • Ultrathin SiO x prepared by in-line plasma-assisted N 2 O oxidation (PANO) is used for passivated contact. • Passivated contact with PANO SiO x shows competitive quality to that with NASO SiO x. • Champion surface passivation reaches i V oc = 747 mV & J 0 = 2.0 fA/cm2 after hydrogenation. • Contact resistivity becomes <10 mΩ cm2 if annealing temperature is > 820 °C. • Oxidation degree, thickness, and pinhole are characterized for robust passivated contact with PANO SiO x. [ABSTRACT FROM AUTHOR]

In this work, we investigated the gettering of the in-situ phosphorus-doped polysilicon passivating contact that was realized through plasma-enhanced chemical-vapor deposition (PECVD) technology. Interstitial iron (Fe i) induced artificially was used as the marker for estimating gettering effectiveness. The factors on gettering effectiveness are studied, including the fabrication procedures and the structures of the polysilicon passivating contact. The research suggests that the heavily phosphorus-doped polysilicon layer serves as the gettering pool for iron atoms. We found that the measures including raising the annealing temperature, extending the annealing time, increasing the thickness and doping concentration of polysilicon, and lowering the SiO x thickness are helping to improve the gettering effectiveness. Moreover, the subsequent hydrogenation promotes the lifetime and implied open-circuit voltage by reducing Shockley-Read-Hall (SRH) recombination. The advantage of the polysilicon passivating contact is the significant effect on the improvement in bulk lifetime, so that the low-quality silicon wafer has the chance to be used for solar cell fabrication with notably improved performance by using the excellent gettering and surface passivation of the polysilicon passivating contact. In summary, this work confirmed that the PECVD-prepared in-situ doped polysilicon passivating contact is an effective process to remove more than 99.99% bulk Fe contamination with an optimal formation procedure, which was essential for the industrial manufacture for silicon solar cells. • In-situ doped polysilicon junction prepared by PECVD shows excellent gettering capability. • Different measures for improving gettering effectiveness are investigated. • Phosphorus-doped polysilicon layer is considered as gettering pool for iron atoms. • Polysilicon junction prepared by PECVD is able to remove >99.99% Fe i contamination. • Champion iV oc of >720 mV after getter is achieved with an original Fe i of ~1 × 1013cm-3. [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]

Tin oxide (SnO 2 ) is widely used in perovskite solar cells (PSCs) as an electron transport layer (ETL) material. However, its high surface trap density has already become a strong factor limiting PSC development. In this work, phosphoric acid is adopted to eliminate the SnO 2 surface dangling bonds to increase electron collection efficiency. The phosphorus mainly exists at the boundaries in the form of chained phosphate groups, bonding with which more than 47.9% of Sn dangling bonds are eliminated. The reduction of surface trap states depresses the electron transport barriers, thus the electron mobility increases about 3 times when the concentration of phosphoric acid is optimized with 7.4 atom % in the SnO 2 precursor. Furthermore, the stability of the perovskite layer deposited on the phosphate-passivated SnO 2 (P-SnO 2 ) ETL is gradually improved with an increase of the concentration. Due to the higher electron collection efficiency, the P-SnO 2 ETLs can dramatically promote the power conversion efficiency (PCE) of the PSCs. As a result, the champion PSC has a PCE of 21.02%. Therefore, it has been proved that this simple method is efficient to improve the quality of ETL for high-performance PSCs.

To unlock the full potential of the perovskite solar cell (PSC) photocurrent density and power conversion efficiency, the topic of optical management and design optimization is of absolute importance. Here, we propose a gradient-index optical design of the PSC based on a Gaussian-type front-side glass structure. Numerical simulations clarify a broadband light-harvesting response of the new design, showing that a maximal photocurrent density of 23.35  mA/cm 2 may be expected, which is an increase by 1.21  mA/cm 2 compared with that of the traditional flat-glass counterpart (22.14  mA/cm 2 ). Comprehensive analysis of the electric field distributions elucidates the light-trapping mechanism. Furthermore, PSCs having the Gaussian index profile display superior optical properties and performance compared to those of the uniform index counterpart under varying conditions of perovskite layer thicknesses and incident angles. The simulation results in this study provide an effective design scheme to promote optical absorption in PSCs.