Synthesis of Uniquely Structured SnO2 Hollow Nanoplates and Their Electrochemical Properties for Li‐Ion Storage

A new mechanism for the transformation of nanostructured metal selenides into uniquely structured metal oxides via the Kirkendall effect, which results from the different diffusion rates of metal and Se ions and O₂ gas, is proposed. SnSe nanoplates are selected as the first target material and transformed into SnO₂ hollow nanoplates by the Kirkendall effect. SnSe‐C composite powder, in which SnSe nanoplates are attached or stuck to amorphous carbon microspheres, transforms into several tens of SnO₂ hollow nanoplates by a thermal oxidation process under an air atmosphere. Core–shell‐structured SnSe‐SnSe₂@SnO₂, SnSe₂@SnO₂, Se‐SnSe₂@SnO₂, and Se@SnO₂ and yolk–shell‐structured Se@void@SnO₂ intermediates are formed step‐by‐step during the oxidation of the SnSe nanoplates. The uniquely structured SnO₂ hollow nanoplates have superior cycling and rate performance for Li‐ion storage. Additionally, their discharge capacities at the 2nd and 600th cycles are 598 and 500 mA h g^‐1, respectively, and the corresponding capacity retention measured from the 2nd cycle is as high as 84%.     

Growth of Aligned Square‐Shaped SnO2 Tube Arrays

Tin dioxide (SnO₂) box beams, or tubes with square or rectangular cross‐sections, are synthesized on quartz substrates using a combustion chemical vapor deposition (CVD) method in an open atmosphere at 850 °C to 1150 °C. The cross‐sectional width of the as‐synthesized SnO₂ tubules is tunable from 50 nm to sub‐micrometer depending on synthesis temperature. Each tubule is found to be a single crystal of rutile structure with four {110} peripheral surfaces and <001> growth direction. Although several growth patterns are observed for different samples, the basic growth mechanism is believed to be a self‐catalyzed, direct vapor–solid (VS) process, where most new material is incorporated into the bottom parts of the existing SnO₂ tubules through surface diffusion. The tubes are readily aligned in the direction perpendicular to the substrate surface to form tube arrays. These well‐aligned SnO₂ tubule arrays with tunable tube size could be the building blocks or templates for fabrication of functional nanodevices, especially those relevant to energy storage and conversion such as nanobatteries, nanofuel cells, and nanosensors. A gas sensor based on a single SnO₂ nanotubes demonstrated extremely high sensitivity to ethanol vapor.     

Fully High‐Temperature‐Processed SnO2 as Blocking Layer and Scaffold for Efficient,Stable, and Hysteresis‐Free Mesoporous Perovskite Solar Cells

Planar perovskite solar cells (PSCs) based on low‐temperature‐processed (LTP) SnO₂ have demonstrated excellent photovoltaic properties duo to the high electron mobility, wide bandgap, and suitable band energy alignment of LTP SnO₂. However, planar PSCs or mesoporous (mp) PSCs based on high‐temperature‐processed (HTP) SnO₂ show much degraded performance. Here, a new strategy with fully HTP Mg‐doped quantum dot SnO₂ as blocking layer (bl) and a quite thin SnO₂ nanoparticle as mp layer are developed. The performances of both planar and mp PSCs has been greatly improved. The use of Mg‐SnO₂ in planar PSCs yields a high‐stabilized power conversion efficiency (PCE) of close to 17%. The champion of mp cells exhibits hysteresis free and stable performance with a high‐stabilized PCE of 19.12%. The inclusion of thin mp SnO₂ in PSCs not only plays a role of an energy bridge, facilitating electrons transfer from perovskite to SnO₂ bl, but also enhances the contact area of SnO₂ with perovskite absorber. Impedance analysis suggests that the thin mp layer is an “active scaffold” selectively collecting electrons from perovskite and can eliminate hysteresis and effectively suppress recombination. This is an inspiring advance toward high‐performance PSCs with HTP mp SnO₂.     

Hydrothermally Treated SnO2 as the Electron Transport Layer in High‐Efficiency Flexible Perovskite Solar Cells with a Certificated Efficiency of 17.3%

Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO₂ ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO₂ ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO₂ nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO₂ ETLs.     

Dopant‐Free,Amorphous–Crystalline Heterophase SnO2 Electron Transport Bilayer Enables >20% Efficiency in Triple‐Cation Perovskite Solar Cells

Improving the ohmic contact and interfacial morphology between an electron transport layer (ETL) and perovskite film is the key to boost the efficiency of planar perovskite solar cells (PSCs). In the current work, an amorphous–crystalline heterophase tin oxide bilayer (Bi‐SnO₂) ETL is prepared via a low‐temperature solution process. Compared with the amorphous SnO₂ sol–gel film (SG‐SnO₂) or the crystalline SnO₂ nanoparticle (NP‐SnO₂) counterparts, the heterophase Bi‐SnO₂ ETL exhibits improved surface morphology, considerably fewer oxygen defects, and better energy band alignment with the perovskite without sacrificing the optical transmittance. The best PSC device (active area ≈ 0.09 cm²) based on a Bi‐SnO₂ ETL is hysteresis‐less and achieves an outstanding power conversion efficiency of ≈20.39%, which is one of the highest efficiencies reported for SnO₂‐triple cation perovskite system based on green antisolvent. More fascinatingly, large‐area PSCs (active areas of ≈3.55 cm²) based on the Bi‐SnO₂ ETL also achieves an extraordinarily high efficiency of ≈14.93% with negligible hysteresis. The improved device performance of the Bi‐SnO₂‐based PSC arises predominantly from the improved ohmic contact and suppressed bimolecular recombination at the ETL/perovskite interface. The tailored morphology and energy band structure of the Bi‐SnO₂ has enabled the scalable fabrication of highly efficient, hysteresis‐less PSCs.     

White‐Light Emitting Diode Array of p+‐Si/Aligned n‐SnO2 Nanowires Heterojunctions

We report on the fabrication and optoelectronic properties of p‐n heterojunction arrays of p⁺‐type Si and aligned n‐type SnO₂ nanowires with high rectification ratios of >10⁴ at ±15 V. The electrical stability of the p‐n heterojunction devices was improved by coating the junction with poly(methylmethacrylate) to minimize the degradation of the interface layer at the junction. As a photodiode an enhanced UV photosensitivity higher than 10² was recorded under reverse bias. Using a large forward bias in the light‐emitting diode mode white light was emitted from the large‐scale heterojunction devices with at least three broad peaks in the visible range, which can be attributed to the interband transitions of the injected electrons or holes mediated by an interfacial SiO₂ layer with a contribution of trap‐level energies. These results indicate the high potential of Si/SnO₂ nanowires heterojunctions as optoelectronic devices with proper tuning of the recombination center at the junctions.     

General Fabrication of Monolayer SnO2 Nanonets for High‐Performance Ultraviolet Photodetectors

A facile approach for the fabrication of monolayer SnO₂ nanonet is presented using polymer colloid monolayer nanofilms from oil–water interface self‐assembly as sacrificial templates. The hole size of the nanonets can be adjusted easily by the mean diameter of polymer colloidal spheres. This method can be extended to the fabrication of a series of monolayer nanonets of semiconducting oxides such as TiO₂, ZnO, and CeO₂. Furthermore, the first photoresponse nanodevice based on monolayer SnO₂ nanonet is fabricated. This device presents ultrahigh photocurrent and sensitivity, excellent stability, and reproducibility.     

p‐Si/SnO2/Fe2O3 Core/Shell/Shell Nanowire Photocathodes for Neutral pH Water Splitting

Silicon is one of the promising materials for solar water splitting and hydrogen production; however, it suffers from two key factors, including the large external potential required to drive water splitting reactions at its surface and its instability in the electrolyte. In this study, a successful fabrication of novel p‐Si/n‐SnO₂/n‐Fe₂O₃ core/shell/shell nanowire (css‐NW) arrays, consisting of vertical Si NW cores coated with a thin SnO₂ layer and a dense Fe₂O₃ nanocrystals (NCs) shell, and their application for significantly enhanced solar water reduction in a neutral medium is reported. The p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NW structure is characterized in detail using scanning, transmission, and scanning transmission electron microscopes. The p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NWs show considerably improved photocathodic performances, including higher photocurrent and lower photocathodic turn‐on potential, compared to the bare p‐Si NWs or p‐Si/n‐SnO₂ core/shell NWs (cs‐NWs), due to increased optical absorption, enhanced charge separation, and improved gas evolution. As a result, photoactivity at 0 V versus reversible hydrogen electrode and a low onset potential in the neutral solution are achieved. Moreover, p‐Si/n‐SnO₂/n‐Fe₂O₃ css‐NWs exhibit long‐term photoelectrochemical stability due to the Fe₂O₃ NCs shell well protection. These results reveal promising css‐NW photoelectrodes from cost‐effective materials by facile fabrication with simultaneously improved photocathodic performance and stability.     

Laser‐Ablation Growth and Optical Properties of Wide and Long Single‐Crystal SnO2 Ribbons

Wide and long ribbons of single‐crystalline SnO₂ have been achieved via laser ablation of a SnO₂ target. Transmission electron microscopy (TEM) shows the as‐grown SnO₂ ribbons are structurally perfect and uniform, with widths of 300–500 nm, thicknesses of 30–50 nm (width‐to‐thickness ratio of ～ 10), and lengths ranging from several hundreds of micrometers to the order of millimeters. X‐ray diffraction (XRD) pattern and energy‐dispersive X‐ray spectroscopy (EDS) spectral analysis indicate that the ribbons have the phase structure and chemical composition of the rutile form of SnO₂. Selected‐area electron diffraction (SAED) patterns and high‐resolution TEM images reveal that the ribbons are single crystals and grow along the [100] crystal direction. Photoluminescence measurements show that the synthesized SnO₂ ribbons have one strong emission band at ～ 605 nm and a red‐shift of ～ 30 nm, as compared to standard SnO₂ powder, which may be attributed to crystal defects and residual strains accommodated during the growth of the ribbons.     

Reliable Monolayer‐Template Patterning of SnO2 Thin Films from Aqueous Solution and Their Hydrogen‐Sensing Properties

We demonstrate a novel lithographic technique utilizing a solvent to fabricate a chemically based semiconductor microdevice from an aqueous solution. According to this technique, SnO₂ thin film could be integrated onto predefined sites on a SiO₂/Si wafer. A patterned octadecyltrimethoxysilane self‐assembled monolayer (ODS‐SAM) was prepared by vacuum ultraviolet (VUV) irradiation through a photomask to use as a template for the fabrication of a micropatterned SnO₂ thin film on the SiO₂/Si surface. A Sn‐based thin film was then deposited onto the entire surface of the ODS template from an aqueous solution containing 0.03 mol L^–1 of SnCl₂·2H₂O at 60 °C for 16 h in an ambient atmosphere. The thin film deposited on the methyl‐terminated area of the template was then peeled using an ultrasonic rinse in anhydrous toluene for 30 min, while the film deposited on the silanol area remained intact and undamaged. Rinsing in hydrophilic solvents did not facilitate peeling of the thin film from the methyl‐terminated area. We succeeded by this process in obtaining a high‐resolution, micropatterned Sn‐based thin film on an ODS‐SAM template on Si. The as‐deposited film was composed of fine Sn‐based particles. The sensitivity of this SnO₂ thin film to H₂ gas increases linearly with improving crystallinity. The effectiveness of anhydrous toluene as a rinse in solution lithography is discussed from the viewpoint of the high hydrophobic affinity between the rinse solvent and the terminal groups in the monolayer template.     

High‐Performance Amorphous Multilayered ZnO‐SnO2 Heterostructure Thin‐Film Transistors: Fabrication and Characteristics

Multilayered ZnO‐SnO₂ heterostructure thin films consisting of ZnO and SnO₂ layers are produced by alternating the pulsed laser ablation of ZnO and SnO₂ targets, and their structural and field‐effect electronic transport properties are investigated as a function of the thickness of the ZnO and SnO₂ layers. The performance parameters of amorphous multilayered ZnO‐SnO₂ heterostructure thin‐film transistors (TFTs) are highly dependent on the thickness of the ZnO and SnO₂ layers. A highest electron mobility of 43 cm²/V·s, a low subthreshold swing of a 0.22 V/dec, a threshold voltage of 1 V, and a high drain current on‐to‐off ratio of 10¹⁰ are obtained for the amorphous multilayered ZnO(1.5 nm)‐SnO₂(1.5 nm) heterostructure TFTs, which is adequate for the operation of next‐generation microelectronic devices. These results are presumed to be due to the unique electronic structure of amorphous multilayered ZnO‐SnO₂ heterostructure film consisting of ZnO, SnO₂, and ZnO‐SnO₂ interface layers.     

Enhanced Stability of Perovskite Solar Cells with Low‐Temperature Hydrothermally Grown SnO2 Electron Transport Layers

Perovskite solar cells (PSCs) may offer huge potential in photovoltaic conversion, yet their practical applications face one major obstacle: their low stability, or quick degradation of their initial efficiencies. Here, a new design scheme is presented to enhance the PSC stability by using low‐temperature hydrothermally grown hierarchical nano‐SnO₂ electron transport layers (ETLs). The ETL contains a thin compact SnO₂ layer underneath a mesoporous layer of SnO₂ nanosheets. The mesoporous layer plays multiple roles of enhancing photon collection, preventing moisture penetration and improving the long‐term stability. Through such simple approaches, PSCs with power conversion efficiencies of ≈13% can be readily obtained, with the highest efficiency to be 16.17%. A prototypical PSC preserves 90% of its initial efficiency even after storage in air at room temperature for 130 d without encapsulation. This study demonstrates that hierarchical SnO₂ is a potential ETL for fabricating low‐cost and efficient PSCs with long‐term stability.     

Epitaxial Growth of Branched α‐Fe2O3/SnO2 Nano‐Heterostructures with Improved Lithium‐Ion Battery Performance

We report the synthesis of a novel branched nano‐heterostructure composed of SnO₂ nanowire stem and α‐Fe₂O₃ nanorod branches by combining a vapour transport deposition and a facile hydrothermal method. The epitaxial relationship between the branch and stem is investigated by high resolution transmission electron microscopy (HRTEM). The SnO₂ nanowire is determined to grow along the [101] direction, enclosed by four side surfaces. The results indicate that distinct crystallographic planes of SnO₂ stem can induce different preferential growth directions of secondary nanorod branches, leading to six‐fold symmetry rather than four‐fold symmetry. Moreover, as a proof‐of‐concept demonstration of the function, such α‐Fe₂O₃/SnO₂ composite material is used as a lithium‐ion batteries (LIBs) anode material. Low initial irreversible loss and high reversible capacity are demonstrated, in comparison to both single components. The synergetic effect exerted by SnO₂ and α‐Fe₂O₃ as well as the unique branched structure are probably responsible for the enhanced performance.     

Solvent‐Assisted Low‐Temperature Crystallization of SnO2 Electron‐Transfer Layer for High‐Efficiency Planar Perovskite Solar Cells

A high‐quality polycrystalline SnO₂ electron‐transfer layer is synthesized through an in situ, low‐temperature, and unique butanol–water solvent‐assisted process. By choosing a mixture of butanol and water as a solvent, the crystallinity is enhanced and the crystallization temperature is lowered to 130 °C, making the process fully compatible with flexible plastic substrates. The best solar cells fabricated using these layers achieve an efficiency of 20.52% (average 19.02%) which is among the best in the class of planar n–i–p‐type perovskite (MAPbI₃) solar cells. The strongly reduced crystallization temperature of the materials allows their use on a flexible substrate, with a resulting device efficiency of 18%.     

Tin Dioxide Sensing Layer Grown on Tubular Nanostructures by a Non‐Aqueous Atomic Layer Deposition Process

A new atomic layer deposition (ALD) process for nanocrystalline tin dioxide films is developed and applied for the coating of nanostructured materials. This approach, which is adapted from non‐hydrolytic sol‐gel chemistry, permits the deposition of SnO₂ at temperatures as low as 75 °C. It allows the coating of the inner and outer surface of multiwalled carbon nanotubes with a highly conformal film of controllable thickness. The ALD‐coated tubes are investigated as active components in gas‐sensor devices. Due to the formation of a p‐n heterojunction between the highly conductive support and the SnO₂ thin film an enhancement of the gas sensing response is observed.     

Gas Sensors: Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading (Adv. Funct. Mater. 24/2010)

This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO₂ fibers. Unloaded and Pd‐loaded SnO₂ nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO₂ crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO₂ crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO₂ grain growth during the calcination step. The Pd‐loaded SnO₂ sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H₂ and lower sensitivity to NO₂ compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO₂ crystallites and catalytic effect of PdO in promoting the oxidation of H₂ into H₂O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.     

Thin‐Wall Assembled SnO2 Fibers Functionalized by Catalytic Pt Nanoparticles and their Superior Exhaled‐Breath‐Sensing Properties for the Diagnosis of Diabetes

Hierarchical SnO₂ fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO₂ tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin‐walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO₂ layers. Highly porous SnO₂ fibers synthesized at a high flow rate show five‐fold higher acetone responses than densely packed SnO₂ fibers synthesized at a low flow rate. Interestingly, thin‐wall assembled SnO₂ fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un‐doped SnO₂ fibers, even at low acetone concentrations. Moreover, Pt‐decorated SnO₂ fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin‐wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer.     

Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading

This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO₂ fibers. Unloaded and Pd‐loaded SnO₂ nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO₂ crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO₂ crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO₂ grain growth during the calcination step. The Pd‐loaded SnO₂ sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H₂ and lower sensitivity to NO₂ compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO₂ crystallites and catalytic effect of PdO in promoting the oxidation of H₂ into H₂O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.     

Amorphous Zinc Stannate (Zn2SnO4) Nanofibers Networks as Photoelectrodes for Organic Dye‐Sensitized Solar Cells

A new strategy for developing dye‐sensitised solar cells (DSSCs) by combining thin porous zinc tin oxide (Zn₂SnO₄) fiber‐based photoelectrodes with purely organic sensitizers is presented. The preparation of highly porous Zn₂SnO₄ electrodes, which show high specific surface area up to 124 m²/g using electrospinning techniques, is reported. The synthesis of a new organic donor‐conjugate‐acceptor (D‐π‐A) structured orange organic dye with molar extinction coefficient of 44 600 M^?1 cm^?1 is also presented. This dye and two other reference dyes, one organic and a ruthenium complex, are employed for the fabrication of Zn₂SnO₄ fiber‐based DSSCs. Remarkably, organic dye‐sensitized DSSCs displayed significantly improved performance compared to the ruthenium complex sensitized DSSCs. The devices based on a 3 μm‐thick Zn₂SnO₄ electrode using the new sensitizer in conjunction with a liquid electrolyte show promising photovoltaic conversion up to 3.7% under standard AM 1.5G sunlight (100 mW cm^?2). This result ranks among the highest reported for devices using ternary metal oxide electrodes.     

One‐Step Hydrothermal Synthesis of 2D Hexagonal Nanoplates of α‐Fe2O3/Graphene Composites with Enhanced Photocatalytic Activity

There has been significant progress in the field of semiconductor photocatalysis, but it is still a challenge to fabricate low‐cost and high‐activity photocatalysts because of safety issues and non‐secondary pollution to the environment. Here, 2D hexagonal nanoplates of α‐Fe₂O₃/graphene composites with relatively good distribution are synthesized for the first time using a simple, one‐step, template‐free, hydrothermal method that achieves the effective reduction of the graphene oxide (GO) to graphene and intimate and large contact interfaces of the α‐Fe₂O₃ nanoplates with graphene. The α‐Fe₂O₃/graphene composites showed significantly enhancement in the photocatalytic activity compared with the pure α‐Fe₂O₃ nanoplates. At an optimal ratio of 5 wt% graphene, 98% of Rhodamine (RhB) is decomposed with 20 min of irradiation, and the rate constant of the composites is almost four times higher than that of pure α‐Fe₂O₃ nanoplates. The decisive factors in improving the photocatalytic performance are the intimate and large contact interfaces between 2D hexagonal α‐Fe₂O₃ nanoplates and graphene, in addition to the high electron withdrawing/storing ability and the highconductivity of reduced graphene oxide (RGO) formed during the hydrothermal reaction. The effective charge transfer from α‐Fe₂O₃ nanoplates to graphene sheets is demonstrated by the significant weakening of photoluminescence in α‐Fe₂O₃/graphene composites.