Ultrathin SiO2 Research Articles

Ultrathin Al-doped SiO x passivating hole-selective contacts formed by a simple wet process

Ultrathin Al-doped Si oxide (SiO x ) layers were formed by a simple wet chemical treatment, and their hole-selective passivating contact and electrical properties were investigated. From the evaluated contact resistivity (ρ c) and saturation current density (J 0), carrier selectivity (S 10) was estimated to be 13.3. Moreover, in Si nitride (SiN y )/Al-doped SiO x stacks, negative values of fixed charge density (Q f) were obtained, despite a high positive Q f existing in the single SiN y layer. This result implies that Al-doped SiO x has high negative fixed charges and overcompensates the charge polarity in the stacks, which forms an inversion layer and accumulates holes on the Si surface. Furthermore, the negative fixed charges realize excellent carrier separation by the induced upward band bending. In addition, we proposed a novel device architecture named Al-induced charged oxide inversion layer solar cells and confirmed device operation in a simple device configuration.

Room Temperature Light Emission from Superatom-like Ge-Core/Si-Shell Quantum Dots.

We have demonstrated the high-density formation of super-atom-like Si quantum dots with Ge-core on ultrathin SiO2 with control of high-selective chemical-vapor deposition and applied them to an active layer of light-emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge-core, reflecting the type II energy band discontinuity between the Si-clad and Ge-core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near-infrared region and is attributed to radiative recombination between quantized states in the Ge-core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si-based light-emitting devices that are highly compatible with Si-ultra-large-scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics.

High‐performance perovskite/silicon heterojunction solar cells enabled by industrially compatible postannealing

AbstractIn recent years, developing dopant‐free carrier‐selective contacts, instead of heavily doped Si layer (either externally or internally), for crystalline silicon (c‐Si) solar cells have attracted considerable interests with the aim to reduce parasitic light absorption and fabrication cost. However, the stability still remains a big challenge for dopant‐free contacts, especially when thermal treatment is involved, which limits their industrial adoption. In this study, a perovskite material ZnTiO3 combining with an ultrathin (~1 nm) SiO2 film and Al layer is used as an electron‐selective contact, forming an isotype heterojunction with n‐type c‐Si. The perovskite/c‐Si heterojunction solar cells exhibit a performance‐enhanced effect by postmetallization annealing when the annealing temperature is 200–350°C. Thanks to the postannealing treatment, an impressive efficiency of 22.0% has been demonstrated, which is 3.5% in absolute value higher than that of the as‐fabricated solar cell. A detailed material and device characterization reveal that postannealing leads to the diffusion of Al into ZnTiO3 film, thus doping the film and reducing its work function. Besides, the coverage of SiO2 is also improved. Both these two factors contribute to the enhanced passivation effect and electron selectivity of the ZnTiO3‐based contact and hence improve the cell performance.

Room temperature synthesis of highly stable near-infrared FAPbI3@TEOS perovskite phosphor for NIR light-emitting diodes

In some medical laboratory tests, a sampling method via intravenous injection is required. Previous research pointed out using near-infrared (NIR) light vein detectors to reduce erroneous injections. Therefore, low-cost, high-efficiency and stability NIR phosphors are highly essential. Herein, high-stability, ultrathin SiO2 wrapped NIR-CH(NH2)2PbI3 (FAPbI3) perovskite nanocrystals (NCs) are successfully manufactured via one-step method at room temperature atmospheric synthesis. By optimizing the hydrolytic condensation conditions of tetraethoxysilane (TEOS), the resulting FAPbI3@SiO2 perovskite NCs phosphors exhibits a high photoluminescence quantum yields (PLQYs) of 57.2% and improves water resistance and thermostability. The low-cost NIR light-emitting diodes (NIR-LEDs) fabricated by coating NIR-FAPbI3@SiO2 perovskite NCs phosphors on commercial blue InGaN LEDs chip demonstrated a ∼787 nm EL spectra of NIR-LEDs under the startup voltage of 2.6 V. Even after 12 h of continuous working, no significant changes were observed in the EL spectra of the NIR-LEDs, which indicates that NIR-FAPbI3@SiO2 perovskite NCs phosphor has high capacity in biological applications.

Photocatalytic formation of a gas permeable layer selectively deposited on supported metal nanoparticles for sintering-resistant thermal catalysis.

Nanoparticle aggregation of supported metal catalysts at high temperatures is a serious problem that causes a drop in catalytic performance. This study investigates the protection of metal nanoparticles from sintering by selectively forming nanoscale SiO2 shells on Pd supported on TiO2 by ultraviolet (UV) light irradiation. The proton-coupled reduction reaction increases the local pH around Pd nanoparticles, resulting in hydrolysis of tetraethoxyorthosilicate (TEOS) in only the vicinity of the metal. An apparent quantum efficiency of only 0.6% is obtained for the Pd/TiO2 catalyst in H2 evolution from ethanol-containing water under 370 nm excitation light. Therefore, the pH of raw slurry solution should be precisely controlled to that slightly below the threshold value for the TEOS hydrolysis reaction before the photodeposition. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) clearly show that the particle size of the Pd nanoparticles (∼40 nm) with the SiO2 shell (∼20 nm) was almost unchanged by the high-temperature treatment at 900 °C in air, suggesting that the SiO2 shell prevented thermal aggregation of Pd nanoparticles. The Pd/TiO2 without SiO2 shell decoration exhibited a drop in the number of active sites, which was likely due to aggregation of the Pd catalysts. However, the number of active sites on the Pd@SiO2/TiO2 catalyst was maintained even after the catalyst was calcined at 900 °C. Consequently, the Pd@SiO2/TiO2 catalyst maintained its catalytic performance for simulated exhaust gas purification even after treatment at 900 °C. This study presents a methodology to produce sintering-tolerant supported metal nanoparticles using the photocatalytic gas permeable layer fabrication method.

Multimodal Encapsulation to Selectively Permeate Hydrogen and Engineer Channel Conduction for p-Type SnOx Thin-Film Transistor Applications.

It has been challenging to synthesize p-type SnOx (1 < x < 2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band. Herein, we report on the multifunctional encapsulation of p-SnOx to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOx channel for thin-film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements identified that ultrathin SiO2 as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOx and selectively diffused hydrogen across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current (on/off ratio > 103), field effect mobility of 3.41 cm2/(V s), and threshold voltages of ∼5-10 V. The fabricated devices show minimal deviations as small as ±6% in the TFT performance parameters, which demonstrates good reproducibility of the fabrication process. The relevance between the TFT performance and the effects of hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. Density functional theory calculations reveal that hydrogen-related impurity complexes are in charge of the enhanced channel conductance with gate biases, which further supports the selective permeation of hydrogen through a thin SiO2 encapsulation.

Gas permeation rates of ultrathin graphite sealed SiO2 cavities.

Despite the proven impermeability of graphene toward most standard gases, graphene/graphite sealed SiO2 cavities always exhibit a nonzero leak rate, and the physical leakage mechanism is still unclear. By measuring leak rates of different gases for the same cavities sealed by ultrathin graphite under identical conditions, we find that the leak rates generally depend on the kinetic diameter of the gas molecules, which implies that the leakage is caused by a molecular sieving mechanism. By comparing different samples, we find that the leak rate of any gas in a particular sample is well predicted by the leak rate of N2 in that sample. In addition, we observe enhanced leak rates of water-soluble molecules. We infer that the leakage path (i.e., the graphene/graphite-SiO2 interface) favors hydrophilic species.

(Digital Presentation) Multimodal Encapsulation of p-SnOx to Engineer the Carrier Density for Thin Film Transistor Applications

It has been challenging to synthesize p-type SnOx (1≤x<2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band.We recently reported on the processing of p-type SnOx and an oxide-based p-n heterostructures, demonstrating high on/off rectification ratio (>103), small turn-on voltage (<0.5 V), and low saturation current (~1×10-10 A)1. In order to further understand the p-type oxide and engineer the properties for various electronic device applications, it is important to identify (or establish) the dominating doping and transport mechanisms. The low dopability in p-type SnOx, of which the causation is also closely related to the narrow processing window, needs to be mitigated so that the electrical properties of the material are to be adequately engineered 2, 3.Herein, we report on the multifunctional encapsulation of p-SnOx to limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOx channel for thin film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry measurements identified that ultra-thin SiO2 as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOx and augmented hydrogen density across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much-enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current. The relevance between the TFT performance and the effects of oxygen suppression and hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. These results are supported by density-functional-theory calculations. Acknowledgement This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education. References Lee, D. H.; Park, H.; Clevenger, M.; Kim, H.; Kim, C. S.; Liu, M.; Kim, G.; Song, H. W.; No, K.; Kim, S. Y.; Ko, D.-K.; Lucietto, A.; Park, H.; Lee, S., High-Performance Oxide-Based p–n Heterojunctions Integrating p-SnOx and n-InGaZnO. ACS Applied Materials & Interfaces 2021, 13 (46), 55676-55686.Hautier, G.; Miglio, A.; Ceder, G.; Rignanese, G.-M.; Gonze, X., Identification and design principles of low hole effective mass p-type transparent conducting oxides. Nat Commun 2013, 4.Yim, K.; Youn, Y.; Lee, M.; Yoo, D.; Lee, J.; Cho, S. H.; Han, S., Computational discovery of p-type transparent oxide semiconductors using hydrogen descriptor. npj Computational Materials 2018, 4 (1), 17. Figure 1

Characterization of Light Emission Properties of Impurity Doped Ge/Si Core–Shell Quantum Dots

We have fabricated valency-controlled Si-QDs with Ge-core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and studied the effect of phosphorus- and boron-doping on Ge-core from their PL properties. During the Ge deposition, delta doping of phosphorus or boron atoms in QDs was carried out by pulse injection using 1% PH3 or B2H6 diluted with He, respectively. No changes in dot size and density with either P- or B-doping were confirmed by AFM topographic images. Under photoexcitation of undoped QDs with a 976-nm line from a semiconductor laser, broad PL spectra consisting of four Gaussian components originating from radiative recombination through quantized states in QDs were observed in the energy range from 0.62 to 0.85 eV without impurity doping even at room temperature. In the doped QDs, relatively-narrow components peaked at ~0.68 eV and ~0.64eV were observed with P-doping and with B-doping to Ge-core, respectively, in addition to the four components seen in undoped QDs. It is interesting noted that, with an increase in B2H6 pulse injection from 1 to 4 times, the integrated PL intensity was enhanced by a factor of 1.4 to 2.4 compared to that of the undoped QDs while no significant change in spectral shape was observable. This can be interpreted in terms of an increase in the number of holes with B-doping to the Ge core since the carrier recombination rates is proportional to the product of the number of electrons and holes confined in QD under weak photoexcitation.

Synergistically enhanced ultraviolet emission of Yb doped ZnO films by using a capping of ultrathin Al and SiO2 microspheres.

We studied the enhancement effects of ultraviolet (UV) emission from rare earth ytterbium (Yb) doped ZnO films, by using capping layers of Al and SiO2 micro-spheres. The films were deposited on Si substrates with magnetron sputtering followed by high temperature (∼1000°C) heat treatment, and then capped with a nanoscale ultrathin aluminum (Al) layer and/or SiO2 micro-spheres on the surface of the films. The photoluminescence (PL) results indicate that compared to the case without any capping, the UV emission is enhanced by a factor ranging from several to dozens times, the films capped with 2.0 nm Al layer and 5.0 µm SiO2 microspheres have the longest highest PL intensity among the samples. The PL enhancements are discussed in terms of increased optical (or electrical) fields around the surface of the films combined with defect passivation after the capping. Our work has proposed a strategy to enhance the UV emissions of ZnO, which will broaden the application potential of ZnO in UV photonics.

Temporal and spatial atomic layer deposition of Al-doped zinc oxide as a passivating conductive contact for silicon solar cells

Recently, stacks consisting of an ultrathin SiO2 coated with atomic-layer-deposited (ALD) Al-doped zinc oxide (ZnO:Al) have been shown to yield state-of-the-art passivation of n-type crystalline silicon surfaces and provide low contact resistivities to n+-doped Si and poly-Si surfaces. Key for achieving good surface passivation are an intentionally-grown SiO2 interlayer, an aluminum oxide (Al2O3) capping layer and a post-deposition anneal, whereas n-type doping of the ZnO is required to achieve a low contact resistivity. In this work, we present the latest results and insights obtained for this contact stack. This includes a study of the minimum required thicknesses of both the ZnO and the Al2O3 capping layer to achieve a high passivation level after post-deposition anneal. Also, we provide details on how to remove the Al2O3 capping layer selectively from the ZnO:Al after the post-deposition anneal using a pH-controlled wet-etch, such that the ZnO:Al can be contacted by a metal. Whereas previous work was based on lab-scale temporal ALD, in this work we highlight the industrialization potential by demonstrating that these layers can be prepared by spatial ALD, yielding good passivation levels on both undiffused n-type and n+-diffused c-Si surfaces. Finally, we demonstrate the capability of ALD to deposit ZnO:Al layers selectively on oxidized regions of an otherwise HF-last treated c-Si surface. Such area-selective deposition opens up potential pathways for local, self-aligned contact formation. Altogether, this work provides valuable insights into the working mechanism and practical aspects of ZnO:Al-based passivating contacts.

Esaki Diode Behavior in Highly Uniform MoS2/Silicon Carbide Heterojunctions

AbstractThe heterogeneous integration with 2D materials enables new functionalities and novel devices in state‐of‐the‐art bulk (3D) semiconductors. In this work, highly uniform MoS2 heterostructures with silicon carbide (4H‐SiC) are obtained by a facile synthesis method, highly compatible with semiconductor fab processing, i.e., the sulfurization of predeposited very‐thin (≈1.2 nm) Mo films at a temperature of 700 °C. Current–voltage characteristics of MoS2/n+‐4H‐SiC junctions collected by conductive atomic force microscopy show a pronounced negative differential resistance even at room temperature, which is a typical manifestation of band‐to‐band tunneling between degenerately p+‐/n+‐doped semiconductors. Here, the degenerate p+‐type doping of MoS2, with Nholes ≈ 4 × 1019 cm−3 evaluated by Raman mapping, is ascribed to the significant MoO3 content in the film, as demonstrated by X‐ray photoelectron spectroscopy analyses. Furthermore, atomic resolution transmission electron microscopy analyses reveal the presence of an ultrathin (≈1 nm) SiO2 tunneling barrier between MoS2 and 4H‐SiC, formed during the sulfurization process. The observation of Esaki diode behavior in MoS2 heterojunctions with 4H‐SiC opens new perspectives for this material system as a platform for ultrafast low‐power consumption digital applications.

Enhanced low-frequency microwave absorption performance of FeNi alloy coated carbon foam assisted by SiO2 layer

The hierarchical structures of carbonized melamine foam modified by FeNi alloy and silicon layer (CMF/FeNi-SiO2) have been fabricated by a magnetron sputtering method. The as-prepared CMF/FeNi-SiO2 composites exhibited a three-dimensional porous structure, with the framework uniformly covered by a FeNi layer with several hundred nanometers and an ultrathin SiO2 layer, which demonstrated soft magnetic properties at room temperature. Moreover, the microwave absorption performance of the foam was investigated in the frequency range from 2 to 18 GHz. The results showed that the microwave absorption performance of CMF/FeNi-SiO2 composite was significantly enhanced in the low-frequency range compared with CMF/FeNi. The minimum reflection loss of CMF/FeNi-SiO2 with an absorption thickness of 4.1 mm was about −53 dB at 3.38 GHz and reached an effective absorption bandwidth of 0.93 GHz (from 2.93 GHz to 3.86 GHz). The frequency bandwidth of 8 GHz (2.35 ~ 6.35 GHz, 8.4 ~ 12.4 GHz) with absorption loss ≤ −10 dB and the frequency bandwidth of 2.05 GHz (2.62 ~ 4.67 GHz) with absorption loss ≤ -20 dB demonstrated the CMF/FeNi-SiO2 a high-efficient absorber in the low-frequency band (2–6 GHz), which stemmed from improved impedance matching and attenuation capacities.

Electroluminescence in metal-oxide-semiconductor tunnel diodes with a crystalline silicon/silicon dioxide quantum well

We investigated electroluminescence (EL) in metal-oxide-semiconductor (MOS) diodes with an indium tin oxide (ITO) film/ultrathin silicon dioxide (SiO2) film/ultrathin crystalline-silicon (Si) layer/buried SiO2 layer/Si substrate structure at a negative voltage applied to the ITO film. The EL peak shifted toward higher energy with decreasing Si-layer thickness. The dependence of the EL-peak energy on the Si-layer thickness shows that the EL is due to one-dimensional quantum confinement. Characterization of the MOS diodes suggested that electrons tunneling through the ultrathin SiO2 film from the conduction band (CB) of the ITO film are injected into higher energy states in the CB of the ultrathin Si layer with a negative voltage applied to the ITO film, and the tunneling electrons radiatively recombine with holes accumulated near the Si/SiO2 interface in the ultrathin Si layer.

Dipole formation and electrical properties of high-k/SiO2 interface according to the density of SiO2 interfacial layer

The effect of SiO₂ buffer layers with various atomic densities on the interface dipole of high-k/SiO2 is confirmed. An ultrathin SiO₂ layer is formed on Si using the plasma-enhanced chemical vapor deposition (PECVD), H2O2 oxidation and nitric acid oxidation (NAOS). The atomic density ratio between the SiO2 layer with various methods and the high-k is calculated respectively. As the oxygen density of the SiO2 increased, the amount of the dipole and the flatband voltage (VFB) shift decreased. Furthermore, leakage current density of the H2O2 (0.9 × 10−2 A/cm2) due to the formation of low-density SiO2, decreases by approximately six orders of magnitude when SiO2 buffer layer is inserted using the NAOS (5.13 × 10-8 A/cm2). Consequently, it is demonstrated that the dipoles that affects the VFB shift is formed by the diffusion of oxygen ions between the high-k and SiO2 interface, which has a significant effect of the MOS capacitor.

Transparent ultrathin SiO2 nanowire aerogel displaying novel properties when interacting with water: A promising versatile functional platform

With low density, high porosity, and outstanding physicochemical stability, ceramic nanowire aerogels and sponges exhibit various interesting properties. Herein, an ultrathin silica nanowire aerogel (SiO2 NWs-A) was achieved via a facile chemical vapor deposition route. In addition to good mechanical and thermal performances, properties resulting from active water-aerogel interactions are revealed, i.e., outstanding transparency, strong capillary effect, enhanced compressive strength (a reversible strain of ∼62%), switchable wettability and robust shape retention ability when filled with water. The physical mechanism related to these interesting properties is demonstrated basically according to its unique features (distinctly reduced nanowire diameter, enriched nanoscopic gap channels, and reinforced network). To demonstrate the superiority, an advantageous solar vapor generation system (hydrophilic NWs-A/reduced graphene oxide (rGO)/ hydrophobic NWs-A) was obtained by integrating these favorable characteristics, giving rise to remarkably promoted vapor evaporation rate and energy efficiency compared to the rGO hydrophobic NWs-A device. These results contribute to the structural design and functional exploration of nanowire aerogels.

High Electric Field Sensing in Ultrathin SiO₂ and Tunnel Region to Enhance GaInP/Si Dual Junction Solar Cell Performance

The Si material is widely used by the manufacturers for sensing applications, because of its abundance. Better carrier sensing capability provide high performance. Solar cell is a sensor, which can sense the sun spectrum to convert it into electrical energy. This paper presents enhancement of passivation quality of GaInP/Si dual junction solar cell by enhancing the carrier transport through tunnel oxide. Reducing the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness increases the transport channel, thereby increasing the electric filed. This enhanced electric field accelerates the carrier transport in the passivation layer, and ultimately the passivation quality improves due to enhanced carries. The high electric field sensing accelerates the majority carriers towards the rear surface. Here, the improvement of the passivation quality is achieved via scaling down the oxide thickness as explained in the MIS tunneling theory. Reduction in oxide thickness provide more transport channels for the carriers, hence improves the tunneling process. Improved carrier sensing in 300nm-1100nm wavelength range, can progress towards the thermodynamic limit of open circuit voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\textit {oc}}$ </tex-math></inline-formula> ). Also, we have used a wide-bandgap tunnel junction to electrically connect two cells, to see the effect on spectrum loss. The thickness and doping concentration of the tunnel junction plays very important role in tunneling process. Sharp edges and fast tunneling of the tunnel junction is the key element in proper current matching process. Numerical analysis of tunnel oxide thickness variation and wide-bandgap tunnel junction is done to obtain the optimum efficiency of 36.22% under 1-Sun concentration.

NiOx/MoOx bilayer as an efficient hole-selective contact in crystalline silicon solar cells

Designing effective carrier-selective contact is a prerequisite for high-efficiency crystalline silicon ( c -Si) solar cells. Compared to doped silicon thin films, wide-band-gap transition metal oxides (TMOs) feature low parasitic absorption, but their carrier selectivity and passivation being poor leads to a mediocre cell efficiency. Herein, we introduce a NiO x /MoO x bilayer as an efficient hole-selective contact in c -Si solar cells. A power conversion efficiency (PCE) of 21.31% is achieved using NiO x /MoO x bilayer, outperforming cells with a single layer of NiO x or MoO x . Upon depositing NiO x on MoO x , interfacial reactions modify the stoichiometry and defect chemistry in both oxides, leading to a band alignment beneficial for hole selectivity. By inserting a SiO x tunneling layer on c -Si surface to further suppress recombination, we achieve a PCE of 21.60% (fill factor 83.34%). Our work highlights a promising approach to improve the performance of dopant-free c -Si solar cells by employing cost-effective TMOs as hole-selective contact. A NiO x /MoO x bilayer as an efficient hole-selective contact in p -Si solar cells Interfacial reaction of NiO x /MoO x modifies doping thus band alignment p -Si solar cells with NiO x/ MoO x bilayer show efficiency of 21.31% Inserting an ultra-thin SiO x tunneling layer boosts to an efficiency of 21.60% Li et al. report a NiO x /MoO x bilayer as an efficient hole-selective contact in p -Si heterojunction solar cells, delivering an efficiency of 21.31%. Inserting an additional ultra-thin SiO x tunneling layer further boosts open-circuit voltage and fill factor, resulting in an efficiency of 21.60%. This work provides a design strategy to push forward the development of c -Si solar cells with transition metal oxides as hole-selective contact.

Atomic-layer-deposited Al-doped zinc oxide as a passivating conductive contacting layer for n+-doped surfaces in silicon solar cells

Stacks consisting of an ultrathin SiO 2 coated with atomic-layer deposited (ALD) zinc oxide (ZnO) and aluminum oxide (Al 2 O 3 ) have been shown to yield state-of-the-art passivation of n -type crystalline silicon surfaces. The distinguishing aspect of this novel passivation stack is the very conductive nature of the passivating ZnO layer. In this work, it is demonstrated that such a stack can provide additional functionalities relevant for silicon solar cells. Specifically, it is shown that the conductive and transparent stacks can passivate textured and n + -diffused silicon surfaces and that they can form an Ohmic contact to n + -diffused surfaces with a low contact resistivity, provided the ZnO is Al-doped. The Al 2 O 3 capping layer has previously been shown to be crucial in the passivation mechanism by preventing the effusion of hydrogen during annealing. Here, it is demonstrated to enable a significant improvement in both the transparency and lateral conductivity of the ZnO upon annealing as well, up to a level typically only attainable by In-based transparent conductive oxides. It is furthermore shown that the passivation of the stacks is thermally stable up to 500–600 o C, depending on the preparation method for the interfacial SiO 2 . Together, these properties make the presented stack an interesting building block for crystalline silicon solar cells, with possibilities for integration as passivating front contact in Passivated Emitter and Rear Cell (PERC)-like solar cells, e.g. as bottom cell top contact in silicon-perovskite tandem cells, as well as a conductive hydrogenation source for poly-Si passivating contacts. • SiO 2 /ALD ZnO:Al/Al 2 O 3 stacks yield excellent passivation of n -type, textured c -Si. • Contact resistivities as low as 15 mΩcm 2 on n + -doped silicon surfaces were obtained. • Doping of the c-Si and ZnO:Al is crucial for obtaining a low contact resistivity. • ALD ZnO:Al can be made highly conductive and transparent by capping and annealing. • The stack has potential in PERC, poly-Si contact and c -Si/perovskite tandem cell.

Core-Shell Structured C@SiO2 Hollow Spheres Decorated with Nickel Nanoparticles as Anode Materials for Lithium-Ion Batteries.

Silicon oxide is regarded as a promising anode material for lithium-ion batteries owing to high theoretical capacity, abundant reserve, and environmental friendliness. Large volumetric variations during the discharging/charging and intrinsically poor electrical conductivity, however, severely hinder its application. Herein, a core-shell structured composite is constructed by hollow carbon spheres and SiO2 nanosheets decorated with nickel nanoparticles (Ni-SiO2 /C HS). Hollow carbon spheres, as mesoporous cores, not only significantly facilitate the electron transfer but also prominently enhance the mechanical robustness of anode materials, which separately improves the rate performance and the cyclic durability. Besides, ultrathin SiO2 nanosheets, as hierarchical shells, provide abundant electrochemical active surface for capacity increment. Moreover, nickel nanoparticles boost the transport capacity of electrons in SiO2 nanosheets. Such a unique architecture of Ni-SiO2 /C HS guarantees an enhanced discharge capacity (712 mAh g-1 at 0.1 A g-1 ) and prolonged cyclic durability (352 mAh g-1 at 1.0 A g-1 after 500 cycles). The present work offers a possibility for silica-based anode materials in the application of next-generation lithium-ion batteries.