Bifacial concentrator Ag‐free crystalline n‐type Si solar cell

We report results obtained using an innovative approach for the fabrication of bifacial low‐concentrator thin Ag‐free n‐type Cz‐Si (Czochralski silicon) solar cells based on an indium tin oxide/(p⁺nn⁺)Cz‐Si/indium fluorine oxide structure. The (p⁺nn⁺)Cz‐Si structure was produced by boron and phosphorus diffusion from B‐ and P‐containing glasses deposited on the opposite sides of n‐type Cz‐Si wafers, followed by an etch‐back step. Transparent conducting oxide (TCO) films, acting as antireflection electrodes, were deposited by ultrasonic spray pyrolysis on both sides. A copper wire contact pattern was attached by low‐temperature (160°C) lamination simultaneously to the front and rear transparent conducting oxide layers as well as to the interconnecting ribbons located outside the structure. The shadowing from the contacts was ~4%. The resulting solar cells, 25 × 25 mm² in dimensions, showed front/rear efficiencies of 17.6–17.9%/16.7–17.0%, respectively, at one to three suns (bifaciality of ~95%). Even at one‐sun front illumination and 20–50% one‐sun rear illumination, such a cell will generate energy approaching that produced by a monofacial solar cell of 21–26% efficiency. Copyright © 2014 John Wiley & Sons, Ltd.     

All‐Carbon Nanotube‐Based Flexible Field‐Emission Devices: From Cathode to Anode

The fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.     

Trilayer Nanomesh Films with Tunable Wettability as Highly Transparent,Flexible, and Recyclable Electrodes

Metallic mesh materials are promising candidates to replace traditional transparent conductive oxides such as indium tin oxide (ITO) that is restricted by the limited indium resource and its brittle nature. The challenge of metal based transparent conductive networks is to achieve high transmittance, low sheet resistance, and small perforation size simultaneously, all of which significantly relate to device performances in optoelectronics. In this work, trilayer dielectric/metal/dielectric (D/M/D) nanomesh electrodes are reported with precisely controlled perforation size, wire width, and uniform hole distribution employing the nanosphere lithography technique. TiO₂/Au/TiO₂ nanomesh films with small hole diameter (≤700 nm) and low thickness (≤50 nm) are shown to yield high transmittance (>90%), low sheet resistance (≤70 Ω sq^?1), as well as outstanding flexural endurance and feasibility for large area patterning. Further, by tuning the surface wettability, these films are applied as easily recyclable flexible electrodes for electrochromic devices. The simple and cost‐effective fabrication of diverse D/M/D nanomesh transparent conductive films with tunable optoelectronic properties paves a way for the design and realization of specialized transparent electrodes in optoelectronics.     

Synthesis and Rate Performance of Monolithic Macroporous Carbon Electrodes for Lithium‐Ion Secondary Batteries

Three‐dimensionally ordered macroporous (3DOM) materials are composed of well‐interconnected pore and wall structures with wall thicknesses of a few tens of nanometers. These characteristics can be applied to enhance the rate performance of lithium‐ion secondary batteries. 3DOM monoliths of hard carbon have been synthesized via a resorcinol‐formaldehyde sol–gel process using poly(methyl methacrylate) colloidal‐crystal templates, and the rate performance of 3DOM carbon electrodes for lithium‐ion secondary batteries has been evaluated. The advantages of monolithic 3DOM carbon electrodes are: 1) solid‐state diffusion lengths for lithium ions of the order of a few tens of nanometers, 2) a large number of active sites for charge‐transfer reactions because of the material's high surface area, 3) reasonable electrical conductivity of 3DOM carbon due to a well‐interconnected wall structure, 4) high ionic conductivity of the electrolyte within the 3DOM carbon matrix, and 5) no need for a binder and/or a conducting agent. These factors lead to significantly improved rate performance compared to a similar but non‐templated carbon electrode and compared to an electrode prepared from spherical carbon with binder. To increase the energy density of 3DOM carbon, tin oxide nanoparticles have been coated on the surface of 3DOM carbon by thermal decomposition of tin sulfate, because the specific capacity of tin oxide is larger than that of carbon. The initial specific capacity of SnO₂‐coated 3DOM carbon increases compared to that of 3DOM carbon, resulting in a higher energy density of the modified 3DOM carbon. However, the specific capacity decreases as cycling proceeds, apparently because lithium–tin alloy nanoparticles were detached from the carbon support by volume changes during charge–discharge processes. The rate performance of SnO₂‐coated 3DOM carbon is improved compared to 3DOM carbon.     

Mechanical integrity of hybrid indium-free electrodes for flexible devices

Maintaining electrical conductivity, optical transparency, and mechanical integrity against bending and stretching are key requirements for flexible transparent electrodes. Transparent conducting oxides (TCOs) are widely used thin film electrodes in optoelectronic devices. However, these materials are brittle and reducing film thickness to improve their mechanical integrity compromises their electrical performance. Here we combine TCO thin films with metal grids embedded in a polymer substrate to create hybrid electrodes with low sheet resistance and high resilience to bending. Amorphous zinc tin oxide (ZTO) and aluminum-doped zinc oxide (AZO) films sputtered onto polyethylene-terephthalate (PET) substrates with and without embedded metal grids are studied. The hybrid electrodes have an optical absorptance below 5% in the visible range and their electrical sheet resistance is less than 1 Ω/sq. The critical strain for tensile failure is analyzed through a combination of electrical measurements and in-situ observations of crack initiation and propagation during tensile loading. The mean critical strain for failure of the AZO/metal grid is 8.5% and that of the ZTO/metal grid is as high as 10%. The AZO and ZTO films alone present critical strain values around 0.6% and 1% respectively, demonstrating that the addition of the metal grid considerably improves the resistance onset strain of the electrodes far beyond these critical strain limits.     

Aqueous Deposition of Ultraviolet Luminescent Columnar Tin‐Doped Indium Hydroxide Films

Indium tin oxide (ITO) has attracted intense interest as the most important transparent conducting oxide (TCO) that sees wide use in many opto‐electronic and photo‐chemical devices. The goal of this study is to explore the possibility of depositing ITO thin films using a bioinspired aqueous deposition route as an alternative. On the surface of sulfonated‐self assembled monolayers, Sn‐doped indium hydroxide films are obtained via a hydrogen peroxide‐assisted method. As a result, the as‐deposited indium tin hydroxide films possess a single hexagonal phase of In(OH)₃· xH₂O (0 ≤ x ≤ 1) with Sn doping percentage of (1.7 ± 0.2) at % and a column‐like hierachical microstructure. Structural, compositional and property studies, including electron microscopy, X‐ray diffraction, photoelectron spectroscopy, optical transmittance, photoluminescence and four‐probe conductivity measurements, are conducted. The possible mechanism based on oriented attachment is discussed for the film growth. Strong room temperature photoluminescence within the near UV range is observed in the case of Sn‐doped, but not in the one of the pure In(OH)₃· xH₂O films. Annealing of the indium tin hydroxide films above 200 °C gives nanocrystalline Sn:In₂O₃ films with higher UV and visible transparency and electrical conductivity compared with those of pure In₂O₃ films. The influence of annealing atmosphere is investigated.     

Spray‐Coated Silver Nanowires as Top Electrode Layer in Semitransparent P3HT:PCBM‐Based Organic Solar Cell Devices

Silver nanowire (Ag NW) thin films are investigated as top electrodes in semitransparent inverted organic solar cells. The performance of semitransparent poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) organic solar cells with Ag NW top electrode layers is found to match very closely the performance of reference devices based on thermally evaporated, highly reflective metal silver top electrodes. The optical losses of the semitransparent electrodes are investigated in detail and analyzed in terms of transmission, scattering, and reflection losses. The impact on an external back reflector is shown to increase the light harvesting efficiency of optically thin devices. Further analysis of transparent devices under illumination from the indium tin oxide (ITO) backside and through the Ag NW front electrode open the possibility to gain deep insight into the vertical microstructure related devices performance. Overall, Ag NW top electrodes are established as a serious alternative to TCO based electrodes. Semitransparent devices with efficiencies of over η = 2.0% are realized.     

π‐Conjugated Molecules Crosslinked Graphene‐Based Ultrathin Films and Their Tunable Performances in Organic Nanoelectronics

Graphene‐based ultrathin films with tunable performances, controlled thickness, and high stability are crucial for their uses. The currently existing protocols, however, could hardly simultaneously meet these requirements. Using amino‐substituted π‐conjugated compounds, including 1,4‐diaminobenzene (DABNH2), benzidine (BZDNH2), and 5,10,15,20‐tetrakis (4‐aminophenyl)‐21H,23H‐porphine (TPPNH2), as cross‐linkages, a new protocol through which graphene oxide (GO) nanosheets can be anchored on solid supports with a high stability and controlled thickness via a layer‐by‐layer method is presented. A thermal annealing leads to the reduction of the films, and the qualities of the samples can be inherited by the as‐produced reduced GO films (RGO). When RGO films are integrated as source/drain electrodes in OFETs, tunable performances can be realized. The devices based on the BZDNH2‐crosslinked RGO electrodes exhibit similar electrical behaviors as those based on the non‐π‐conjugated compound crosslinked electrodes, while improved performances can be gained when those crosslinked by DABNH2 are used. The performances can be further improved when RGO films crosslinked by TPPNH2 are employed. This work likely paves a new avenue for graphene‐based films of tunable performances, controlled thickness, and high stability.     

Overcoming the Challenges of Freestanding Tin Oxide-Based Composite Anodes to Achieve High Capacity and Increased Cycling Stability

Freestanding electrodes are a promising way to increase the energy density of the batteries by decreasing the overall amount of electrochemically inactive materials. Freestanding antimony doped tin oxide (ATO)-based hybrid materials have not been reported so far, although this material has demonstrated excellent performance in conventionally designed electrodes. Two different strategies, namely electrospinning and freeze-casting, are explored for the fabrication of ATO-based hybrid materials. It is shown that the electrospinning of ATO/carbon based electrodes from polyvinyl pyrrolidone polymer (PVP) solutions was not successful, as the resulting electrode material suffers from rapid degradation. However, freestanding reduced graphene oxide (rGO) containing ATO/C/rGO nanocomposites prepared via a freeze-casting route demonstrates an impressive rate and cycling performance reaching 697 mAh g⁻¹ at a high current density of 4 A g⁻¹, which is 40 times higher as compared to SnO₂/rGO and also exceeds the freestanding SnO₂-based composites reported so far. Antimony doping of the nanosized tin oxide phase and carbon coating are thereby shown to be essential factors for appealing electrochemical performance. Finally, the freestanding ATO/C/rGO anodes are combined with freestanding LiFe_0.2Mn_0.8PO₄/rGO cathodes to obtain a full freestanding cell operating without metal current collector foils showing nonetheless an excellent cycling stability.     

Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony‐Doped Tin Oxide Support

A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO₂ (ATO) microparticles with defined pore size, composition, and open‐porous morphology are synthesized that reach a conductivity of ≈3.6 S cm^?1 and are further used as catalyst support. ATO‐supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrO_x colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO‐supported IrO₂ nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm^?3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A g_Ir^?1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO₂‐supported IrO₂ reference catalyst under the same measurement conditions.     

Insulator‐Conductor Type Transitions in Graphene‐Modified Silver Nanowire Networks: A Route to Inexpensive Transparent Conductors

Silver nanowire coatings are an attractive alternative to indium tin oxide for producing transparent conductors. To fabricate coatings with low sheet resistance required for touchscreen displays, a multi‐layer network of silver nanowires must be produced that may not be cost effective. This problem is counteracted here by modifying the electrical properties of an ultra‐low‐density nanowire network through local deposition of conducting graphene platelets. Unlike other solution‐processed materials, such as graphene oxide, our pristine graphene is free of oxygen functional groups, resulting in it being electrically conducting without the need for further chemical treatment. Graphene adsorption at inter‐wire junctions as well as graphene connecting adjacent wires contributes to a marked enhancement in electrical properties. Using our approach, the amount of nanowires needed to produce viable transparent electrodes could be more than 50 times less than the equivalent pristine high density nanowire networks, thus having major commercial implications. Using a laser ablation process, it is shown that the resulting films can be patterned into individual electrode structures, which is a pre‐requisite to touchscreen sensor fabrication.     

Making Ultrafast High‐Capacity Anodes for Lithium‐Ion Batteries via Antimony Doping of Nanosized Tin Oxide/Graphene Composites

Tin oxide‐based materials attract increasing attention as anodes in lithium‐ion batteries due to their high theoretical capacity, low cost, and high abundance. Composites of such materials with a carbonaceous matrix such as graphene are particularly promising, as they can overcome the limitations of the individual materials. The fabrication of antimony‐doped tin oxide (ATO)/graphene hybrid nanocomposites is described with high reversible capacity and superior rate performance using a microwave assisted in situ synthesis in tert‐butyl alcohol. This reaction enables the growth of ultrasmall ATO nanoparticles with sizes below 3 nm on the surface of graphene, providing a composite anode material with a high electric conductivity and high structural stability. Antimony doping results in greatly increased lithium insertion rates of this conversion‐type anode and an improved cycling stability, presumably due to the increased electrical conductivity. The uniform composites feature gravimetric capacity of 1226 mAh g^?1 at the charging rate 1C and still a high capacity of 577 mAh g^?1 at very high charging rates of up to 60C, as compared to 93 mAh g^?1 at 60C for the undoped composite synthesized in a similar way. At the same time, the antimony‐doped anodes demonstrate excellent stability with a capacity retention of 77% after 1000 cycles.     

DC‐sputtered ZnO:Al as transparent conductive oxide for silicon heterojunction solar cells with µc‐Si:H emitter

Silicon heterojunction (SHJ) solar cells are highly interesting, because of their high efficiency and low cost fabrication. So far, the most applied transparent conductive oxide (TCO) is indium tin oxide (ITO). The replacement of ITO with cheaper, more abundant and environmental friendly material with texturing capability is a promising way to reduce the production cost of the future SHJ solar cells. Here, we report on the fabrication of the SHJ solar cells with direct current‐sputtered aluminum‐doped zinc oxide (ZnO:Al) as an alternative TCO. Furthermore, we address several important differences between ITO and the ZnO:Al layers including a high Schottky barrier at the emitter/ZnO:Al interface and a high intrinsic resistivity of the ZnO:Al layers. To overcome the high Schottky barrier, we suggest employing micro‐crystalline silicon (µc‐Si:H) emitter, which also improves temperature threshold and passivation of the solar cell precursor. In addition, we report on the extensive studies of the effect of the ZnO:Al deposition parameters including layer thickness, oxygen flow, power density and temperature on the electrical properties of the fabricated SHJ solar cells. Finally, the results of our study indicate that the ZnO:Al deposition parameters significantly affect the electrical properties of the obtained solar cell. By understanding and fine‐tuning all these parameters, a high conversion efficiency of 19.2% on flat wafer (small area (5 × 5 mm²) and without any front metal grid) is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono‐Molecular Nucleation Layer

A rapid, solvent free method for the fabrication of highly transparent ultrathin (～8 nm) Au films on glass has been developed. This is achieved by derivatizing the glass surface with a mixed monolayer of 3‐mercaptopropyl(trim­ethoxysilane) and 3‐aminopropyl(trimethoxysilane) via co‐deposition from the vapor phase, prior to Au deposition by thermal evaporation. The mixed mono­layer modifies the growth kinetics, producing highly conductive films (～11 Ω per square) with a remarkably low root‐mean‐square roughness (～0.4 nm) that are exceptionally robust towards UV/O₃ treatment and ultrasonic agitation in a range of common solvents. As such, they are potentially widely applicable for a variety of large area applications, particularly where stable, chemically well‐defined, ultrasmooth substrate electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics. By integrating microsphere lithography into the fabrication process, we also demonstrate a means of tuning the transparency by incorporating a random array of circular apertures into the film. The application of these nanostructured Au electrodes is demonstrated in efficient organic photovoltaic devices where it offers a compelling alternative to indium tin oxide coated glass.     

Large‐Area Chemical Vapor Deposited MoS2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics

2D semiconductors are poised to revolutionize the future of electronics and photonics, much like transparent oxide conductors and semiconductors have revolutionized the display industry. Herein, these two types of materials are combined to realize fully transparent 2D electronic devices and circuits. Specifically, a large‐area chemical vapor deposition process is developed to grow monolayer MoS₂ continuous films, which are, for the first time, combined with transparent conducting oxide (TCO) contacts. Transparent conducting aluminum doped zinc oxide contacts are deposited by atomic layer deposition, with composition tuning to achieve optimal conductivity and band‐offsets with MoS₂. The optimized process gives fully transparent TCO/MoS₂ 2D electronics with average visible‐range transmittance of 85%. The transistors show high mobility (4.2 cm² V^?1 s^?1), fast switching speed (0.114 V dec^?1), very low threshold voltage (0.69 V), and large switching ratio (4 × 10⁸). To our knowledge, these are the lowest threshold voltage and subthreshold swing values reported for monolayer chemical vapor deposition MoS₂ transistors. The transparent inverters show fast switching properties with a gain of 155 at a supply voltage of 10 V. The results demonstrate that transparent conducting oxides can be used as contact materials for 2D semiconductors, which opens new possibilities in 2D electronic and photonic applications.     

Fabrication of Ag nanoparticle/ZnO thin films using dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with photoreduction method and its application

We report a novel method to grow silver nanoparticle/zinc oxide (Ag NP/ZnO) thin films using a dual-plasma-enhanced metal-organic chemical vapor deposition (DPEMOCVD) system incorporated with a photoreduction method. The crystalline quality, optical properties, and electrical characteristics of Ag NP/ZnO thin films depend on the AgNO₃ concentration or Ag content and annealing temperature. Optimal Ag NP/ZnO thin films have been grown with a AgNO₃ concentration of 0.12 M or 2.54 at%- Ag content and 500 °C- rapid thermal annealing (RTA); these films show orientation peaks of hexagonal-wurtzite-structured ZnO (002) and face-center-cubic-crystalline Ag (111), respectively. The transmittance and resistivity for optimal Ag NP/ZnO thin films are 85% and 6.9×10⁻⁴ Ω cm. Some Ag NP/ZnO transparent conducting oxide (TCO) films were applied to InGaN/GaN LEDs as transparent conductive layers. The InGaN/GaN LEDs with optimal Ag NP/ZnO TCO films showed electric and optical performance levels similar to those of devices fabricated with indium tin oxide.     

太阳电池中CdS薄膜的制备及其性能的研究

分别采用化学池沉积(CBD)和真空蒸发法,在三种衬底(玻片、ITO玻片、SnO2玻片)上沉积CdS薄膜,并利用扫描电镜(SEM)、透射光谱、X射线衍射(XRD)等方法对沉积膜进行了测试分析,同时阐述了两种不同方法下CdS膜的生长沉积机制。     

Reduced Graphene Oxide Micromesh Electrodes for Large Area,Flexible, Organic Photovoltaic Devices

A laser‐based patterning technique—compatible with flexible, temperature‐sensitive substrates—for the production of large area reduced graphene oxide micromesh (rGOMM) electrodes is presented. The mesh patterning can be accurately controlled in order to significantly enhance the electrode transparency, with a subsequent slight increase in the sheet resistance, and therefore improve the tradeoff between transparency and conductivity of reduced graphene oxide (rGO) layers. In particular, rGO films with an initial transparency of ≈20% are patterned, resulting in rGOMMs films with a ≈59% transmittance and a sheet resistance of ≈565 Ω sq^?1, that is significantly lower than the resistance of ≈780 Ω sq^?1, exhibited by the pristine rGO films at the same transparency. As a proof‐of‐concept application, rGOMMs are used as the transparent electrodes in flexible organic photovoltaic (OPV) devices, achieving power conversion efficiency of 3.05%, the highest ever reported for flexible OPV devices incorporating solution‐processed graphene‐based electrodes. The controllable and highly reproducible laser‐induced patterning of rGO hold enormous promise for both rigid and flexible large‐scale organic electronic devices, eliminating the lag between graphene‐based and indium–tin oxide electrodes, while providing conductivity and transparency tunability for next generation flexible electronics.     

Low‐Temperature‐Processed Printed Metal Oxide Transistors Based on Pure Aqueous Inks

Additive patterning of transparent conducting metal oxides at low temperatures is a critical step in realizing low‐cost transparent electronics for display technology and photovoltaics. In this work, inkjet‐printed metal oxide transistors based on pure aqueous chemistries are presented. These inks readily convert to functional thin films at lower processing temperatures (T ≤ 250 °C) relative to organic solvent‐based oxide inks, facilitating the fabrication of high‐performance transistors with both inkjet‐printed transparent electrodes of aluminum‐doped cadmium oxide (ACO) and semiconductor (InO_x ). The intrinsic fluid properties of these water‐based solutions enable the printing of fine features with coffee‐ring free line profiles and smoother line edges than those formed from organic solvent‐based inks. The influence of low‐temperature annealing on the optical, electrical, and crystallographic properties of the ACO electrodes is investigated, as well as the role of aluminum doping in improving these properties. Finally, the all‐aqueous‐printed thin film transistors (TFTs) with inkjet‐patterned semiconductor (InO_x ) and source/drain (ACO) layers are characterized, which show ideal low contact resistance (R _c < 160 Ω cm) and competitive transistor performance (µ _lin up to 19 cm² V^?1 s^?1, Subthreshold Slope (SS) ≤150 mV dec^?1) with only low‐temperature processing (T ≤ 250 °C).     

Polymer Brush Guided Formation of Conformal,Plasmonic Nanoparticle‐Based Electrodes for Microwire Solar Cells

This report explores the use of sacrificial thin polymer films prepared by surface‐initiated polymerization as a template for the fabrication of highly conformal metal nanoparticle solar cell electrodes. As a first proof‐of‐principle, the use of this method is demonstrated to prepare top electrodes on planar and microwire‐based silicon solar cell devices. These metal nanoparticle films are dual functional in that they not only mediate charge transport, but also enhance light capture due to the plasmonic scattering properties of the nanoparticles. Solar cells with a conformal silver nanoparticle‐based electrode layer show short circuit currents that are 46% higher as compared to those exhibit by devices coated with standard indium tin oxide as the electrode. It is anticipated that this methodology will contribute to novel electrode concepts in the next generation solar cells.