Silver Top Electrode Research Articles

Thermally Triggered Interface for Simplified Organic Solar Cells

Organic photovoltaic (OPV) cells are commonly produced by successive printing of four layers on top of a transparent conducting electrode, with the active layer sandwiched in between interlayers followed by the top electrode. Here, the simplification of OPV manufacturing without the need to coat a hole transport layer (HTL) in inverted OPV (n–i–p) is reported. To ensure the required hole selectivity, thermally trigged molecules are directly blended in the active layer during device casting. Following thermal annealing of the complete devices, organosulfur molecules self‐assembled to form a hole–transporting interface between the silver top electrode and the active layer, thereby enabling working devices. Device optimization is performed by varying the concentration of these molecules and the thermal annealing conditions. The performances of the simplified devices approach those of control devices with vacuum‐evaporated MoO3 HTLs. The solar cells exhibit very encouraging thermal and photostabilities. This work opens the route to high efficiency, simplified, and low‐cost organic solar cells.

Resistive Switching Property of Euforbia Cotinifolia Plant Extract for Potential Use in Eco-Friendly Memory Devices

Resistive switching memory devices based on organic materials are intriguing. These devices are biodegradable and nontoxic to living organisms. In this work, using euphorbia cotinifolia plant extract was investigated for its applicability as an active layer of a resistive switching memory device consisting of silver top electrode and indium-doped tin oxide bottom electrode. This study selected Euphorbia cotinifolia because it is a common, prolific and simple-to-grow plant in many South African homes. When the euphorbia cotinifolia plant is broken, an extract resembling milk is emitted. This extract was collected directly onto the bottom electrode, which was then dried at ambient temperature. For top electrode, silver paste was applied. The entire fabrication process was devoid of heat and electricity. The fabricated device showed impressive properties such as memory hysteresis with [Formula: see text], endurance of over [Formula: see text] write/erase cycles, and an impressive retention of [Formula: see text]. Therefore, this system may be a candidate for a nonvolatile and disposable memory device.

Electrochemical metallization in PDMS-graphite composite-based neuromorphic memristor

Organic memristive devices are promising candidates for wearable neuromorphic in-memory computing systems owing to their easiness of fabrication, bio-compatibility, and energy efficiency. Among various organic materials used as the resistive switching layer of memristive devices, polydimethylsiloxane (PDMS) is a stable, hydrophobic, and bio-compatible material and is not much explored. PDMS composite with low-cost graphite as filler material possesses the advantage of easy tuning of the electrical property of the dielectric layer. In this work, PDMS-graphite composite-based memristors with different top electrode materials were studied to identify the mechanism of resistive switching. Electrochemically active materials like copper and silver and electrochemically inert gold were used as the top electrode. Resistive switching was observed only in copper and silver top electrode devices which substantiates the electrochemical metallization (ECM) type switching. The resistive switching devices also possess synapse-like plasticity and paired-pulse facilitation behavior and have potential applications in neuromorphic computing.

Switching facilitated by the simultaneous formation of oxygen vacancies and conductive filaments in resistive memory devices based on thermally annealed TiO2/a-IGZO bilayers

Resistive random access memory (ReRAM) devices have been gaining popularity in recent years as prime contenders to achieve high-performance non-volatile memory, as such devices offer simple structure, good stability, and high performance and low power consumption. Here, we present a resistive memory based on the bilayer of 2 nm TiO2 and 20 nm amorphous indium-gallium-zinc oxide (a-IGZO) thin films. The device is fabricated on a glass substrate with indium-tin-oxide bottom and silver top electrodes. Annealing temperature of the active layer is optimized by a comparative study of the memory devices, resulting in the widest memory window at 350 °C. X-ray photoemission spectroscopy was utilized to assess the change in the film stoichiometry caused by the annealing process. A memory mechanism is proposed with the generation and migration of oxygen vacancies and the formation of conductive filaments. Based on the device characteristics under repeated sweeps, SET and RESET voltages are selected at 2.0 and −2.0 V respectively, with READ voltage at 0.2 V, demonstrating low voltage operation. The optimized ReRAM has good retention stability for more than 1000 s and its endurance stability exceeds 500 s. The applicability is demonstrated in a circuit with an a-IGZO-based thin film transistor.

Multi-Level Resistive Switching in SnSe/SrTiO3 Heterostructure Based Memristor Device.

Multilevel resistive switching in memristive devices is vital for applications in non-volatile memory and neuromorphic computing. In this study, we report on the multilevel resistive switching characteristics in SnSe/SrTiO3(STO) heterojunction-based memory devices with silver (Ag) and copper (Cu) top electrodes. The SnSe/STO-based memory devices present bipolar resistive switching (RS) with two orders of magnitude on/off ratio, which is reliable and stable. Moreover, multilevel state switching is achieved in the devices by sweeping voltage with current compliance to SET the device from high resistance state (HRS) to low resistance state (LRS) and RESET from LRS to HRS by voltage pulses without compliance current. With Ag and Cu top electrodes, respectively, eight and six levels of resistance switching were demonstrated in the SnSe/SrTiO3 heterostructures with a Pt bottom electrode. These results suggest that a SnSe/STO heterojunction-based memristor is promising for applications in neuromorphic computing as a synaptic device.

Heating-insulating and semitransparent inorganic perovskite solar cells

Heat-insulating semitransparent solar cells, with power-generating and energy-saving functions, have attracted wide attention due to their potential applications in building and automobile integrated photovoltaics. However, it is challenging to simultaneously improve the power conversion efficiency (PCE) and average visible transmittance (AVT) in the wavelength of 400–800 nm for multifunctional semitransparent solar cells. Moreover, as an essential requirement for practical application, the thermal stability is still lacking. In this work, CsPbI2Br inorganic perovskite with high bandgap and superior thermal stability is selected as absorber, combined with ultrathin silver top electrodes for charge collection and infrared reflector, composing the heat-insulating and semitransparent perovskite solar cells (PSCs). By virtue of dual-function ultrathin silver top electrodes, combined with high-index MoOx to further improve visible transmittance, the semitransparent PSCs exhibit PCE of >11% with high AVT of >21%, as well as an outstanding infrared ray energy rejection of >72%. Moreover, the semitransparent inorganic PSCs exhibit superior thermal stability than the organic-inorganic counterparts, remaining 75% and 65% of initial PCE after aging at 85 °C for 200 h in N2 and 105 h in air, respectively. This work paves the way toward realizing high-performance and thermal stable heat-insulating semitransparent solar cells, which greatly enhances their integration into various further applications.

Resistive switching of transition metal ferrites on silicon substrate

This letter reports on the development and characterization of ferrite based resistive switching devices that join the excellent multifunctional memory properties of ferrites and silicon processing technologies. The core of the resistive switching devices consists of a single transition metal ferrite (Co, Cu, Ni, and Zn) confirmed through energy dispersive x-ray spectroscopy and x-ray diffraction. The ferrites are spin coated onto processed silicon dies (acting as bottom electrode/substrate) and deposited with a silver top electrode. Both electrodes are active, providing additional charge carriers to the main redox reaction mechanism (found in ferrites), thus helping device stability. Characterization and analysis of the ferrite-silicon devices show low resistive state ohmic conduction as well as the non-linear conducting mechanisms (Schottky Emission and Poole Frenkel) found in previously reported ferrite resistive switching devices. An additional reaction mechanism (space charge limited current) was found that is attributed to the active electrodes through the influx of excess charge carriers.

Screen-printed MgAl2O4 semi-thick film based highly sensitive and stable capacitive humidity sensor

In this paper we have reported on the excellent humidity sensing properties of screen-printed magnesium aluminate (MgAl2O4) porous, semi-thick film, capacitive sensor in the range of 2%–98% RH. MgAl2O4 nanoparticles were prepared by a facile solid-state reaction route. Screen printing technique was employed to prepare the MgAl2O4 porous semi-thick film. The binders used in screen-printing generated pores on the film surface during firing of the film. The as prepared nanoparticles and the thick film were characterized by different sophisticated techniques, viz. X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), BET-surface area analysis, laser diffraction-based particle size analysis, and contact angle measurement. Parallel plate capacitive configuration was used whereby the sensor film was interposed between copper bottom and silver top electrodes. The sensor exhibited high and stable response up to 98%RH with a detection lower limit of 2%, which is seldom reported. Further we observed low dissipation (<2), fast response (~66 s) and recovery (~71 s) times, low hysteresis (~109 pF at 89% RH), excellent repeatability (at least 15 cycles), and long-term stability (at least 6 months). This sensor is suitable for commercial applications in tea industry, food packaging, hospitals etc.

Self-Assembly and Electrochemical Characterization of Ferrocene-based Molecular Diodes for Solar Rectenna Device

AbstractBailey [1] proposed in 1972 that a nanoscale antenna coupled with a rectifier can harvest broad range electromagnetic radiation from visible to infrared. To incorporate this concept in practical systems, there were two main technological bottle necks that have to be overcome: antenna miniaturization and rectification in terahertz frequency. With current technology and equipment [2], we are proposing a third-generation rectenna-based solar cells composed of Ag nanocubes to harvest ambient visible and infrared electromagnetic waves coupled to ferrocene-based molecular diodes [3] capable of switching at terahertz frequency to convert this received energy into DC power. The function of these molecular diodes is two-fold: they rectify and provide an uniform nano-cavity between silver top electrode and gold bottom electrode. These nano-cavities are capable to support gap plasmon modes and absorption of light in both narrow and broad range, depending on the nanocube size and dispersion. A self-assembled monolayer (SAM) of ferrocene alkane-dithiol is deposited in this nano-cavity making it possible to form molecular sized nano-gaps well below the usual 3 nm, and this structure is robust and reproducible [4]. This SAM can be deposited directly or via a two-step click chemistry on the surface to have along with control over the orientation of the molecule. By tuning the orientation and position of the ferrocene moiety, the direction of rectification can be controlled [3]. Hence, the SAM does not only act as a rectifier but also provides mechanical support combining photonic and electrical properties. This paper focuses on studying the electrical and supramolecular structure of these molecular diode based SAMs.

A relatively wide-bandgap and air-stable donor polymer for fabrication of efficient semitransparent and tandem organic photovoltaics

Organic photovoltaics (OPVs) have attracted tremendous attention in the field of thin-film solar cells due to their wide range of applications, especially for semitransparent devices. Here, we synthesize a dithiaindacenone-thiophene-benzothiadiazole-thiophene alternating donor copolymer named poly{[2,7-(5,5-didecyl-5H-1,8-dithia-as-indacenone)]-alt-[5,5-(5',6'-dioctyloxy-4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]} (PDTIDTBT), which shows a relatively wide bandgap of 1.82 eV, good mobility, and high transmittance and ambient stability. In this work, we fabricate an OPV device using monolayer graphene as top electrode. Due to the stability of PDTIDTBT in air and water, we use a wet transfer technique for graphene to fabricate semitransparent OPVs. We demonstrate OPVs based on the PDTIDTBT:Phenyl-C61/71-butyric acid methyl ester (PCBM) blend with maximum power conversion efficiencies (PCEs) of 6.1 and 4.75% using silver and graphene top electrodes, respectively. Our graphene-based device shows a high average visible transmittance (AVT) of 55%, indicating the potential of PDTIDTBT for window application and tandem devices. Therefore, we also demonstrate tandem devices using the PDTIDTBT:Phenyl-C61-butyric acid methyl ester (PC60BM) blend in both series and parallel connections with average PCEs of 7.3 and 7.95%, respectively. We also achieve a good average PCE of 8.26% with an average open circuit voltage (Voc) of 1.79 V for 2-terminal tandem OPVs using this blend. Based on tandem design, an OPV with PCE of 6.45% and AVT of 38% is demonstrated. Moreover, our devices show improved shelf life and ultraviolet (UV) stability (using CdSe/ZnS core shell quantum dots [QDs]) in ambient with 45% relative humidity.

Effect of ytterbium oxide deposition on microstructural and electrical properties of thin tantalum foil

The effect of ytterbium oxide (174Yb2O3) deposition in modifying the materials and electrical properties of mechanically rolled tantalum (MRTa) thin foil is investigated through electron microscopic, crystallographic, elemental analysis, and current-voltage (I–V) characteristics. A 0.82 μm thick layer of 174Yb2O3 over ∼2.1 μm thick MRTa foil (Yb2O3/Ta) reduces the dimension of surface features, and indicates formation of nanoparticles. The electron beam imaging, energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analysis reveal formation of uniformly distributed Yb2O3 on MRTa surface and chemical inertness of the newly formed Yb2O3/MRTa thin film towards oxidation. The room temperature I–V characteristics of both the MRTa foil and Yb2O3/MRTa thin film tested with silver (Ag) top contact electrodes exhibit ohmic conductions and demonstrate an overall enhancement of 92.1% in electrical conductivity after Yb2O3 thin film deposition on MRTa foil.

Inkjet-printed silver as alternative top electrode for lead zirconate titanate thin films

In the present work, we describe direct patterning of silver top electrodes on polycrystalline Pb(Zr0.53Ti0.47)O3 (PZT) thin films via inkjet printing. The films were first deposited on platinized silicon via chemical solution deposition. Individual nanosilver ink droplets were then printed on the PZT surface to create round top electrodes with tunable diameter from 75 to 93 μm. Printing parameters and strategy were optimized for deposition of homogeneous electrodes. High quality of the printed silver electrodes sintered at 350 °C is confirmed via measurements of the direct piezoelectric response and polarization loops of PZT thin films, whose results are comparable to the ones obtained for sputtered platinum top electrodes, with e31,f = −4.1 C m−2, Pr ∼20 μC cm−2 and Ec ∼55 kV cm−1.

Resistive Switching Memory based on Silver-doped Chitosan Thin Films

AbstractMemristors represent an intriguing two-terminal device strategy potentially able to replace conventional memory devices as well as to support neuromorphic computing architectures. Here, we present the resistive switching behaviour of the sustainable and low-cost biopolymer chitosan, which can be extracted from natural chitin present for instance in crab exoskeletons. The biopolymer films were doped with Ag ions in varying concentrations and sandwiched between a bottom electrode such as fluorinated-tin-oxide and a silver top electrode. Silver-doped devices showed an overall promising resistive switching behaviour for doping concentrations between 0.5 to 1 wt% AgNO3. As bottom electrode fluorinated-tin-oxide, nickel, silver and titanium were studied and multiple write and erase cycles were recorded. However, the overall reproducibility and stability are still insufficient to support broader applicability.

Effect of Ag and Ti electrodes on capacitance tunability of oxygen-deficient SrTiO3 based MIM varactors prepared by plasma sputtering

The role of oxygen deficiencies on the electrical performance of SrTiO3 films is investigated by depositing on the stack of TiN/Ti/SiO2/Si films using radio-frequency (RF) and direct current (DC) magnetron sputtering systems operating in oxygen-deficient plasma environment. Electrodes of silver (Ag) and titanium (Ti) are used to observe the effects of their sizes on the electrical properties of the SrTiO3 films. It is found that the nonlinearity in capacitance–voltage graphs (capacitance tunability) of the varactor can be controlled by varying the electrode area. In addition, the material of the electrode plays a vital role in controlling the non-linearity in the capacitance of the oxygen-deficient SrTiO3 dielectric films with varying voltage. It is found that the silver top electrode instead of titanium, delivers better performance with high capacitance tunability, low leakage current and good quality factor. Post deposition annealing at 550 °C in nitrogen ambient, creates more oxygen deficiencies in SrTiO3 film thereby increasing the linearity of the capacitance–voltage graph and decreasing the capacitance tunability.

Surfaces and Interfaces in the Spotlight

Advanced Materials Interfaces includes topics involving any interface between solids, liquids, and gases. In 2016, articles on vanadium flow batteries, oil/water separation, hole-extraction layers in organic-inorganic hybrid perovskite solar cells, and hybrid membranes as binder-free anodes for high-performance lithium-ion batteries proved to be very popular with our readership. In particular, we would like to congratulate Robert W. Carpick and his team, whose full paper on “Nanoscale Adhesive Properties of Graphene: The Effect of Sliding History” (DOI: 10.1002/admi.201300053) is among our top-cited articles. The Full Papers by Qiang Zhang et al. on “Strongly Coupled Interfaces between a Heterogeneous Carbon Host and a Sulfur-Containing Guest for Highly Stable Lithium-Sulfur Batteries: Mechanistic Insight into Capacity Degradation” (DOI: 10.1002/admi.201400227) and Yabing Qi et al. on “Silver Iodide Formation in Methyl Ammonium Lead Iodide Perovskite Solar Cells with Silver Top Electrodes” (DOI: 10.1002/admi.201500195) are cited equally well. Moreover, some articles have drawn additional attention via news and social media platforms, which is reflected by a high Altmetrics score. The sunlight-induced self-cleaning properties of textiles presented by Rajesh Ramanathan, Vipul Bansal et al. in their work on “Robust Nanostructured Silver and Copper Fabrics with Localized Surface Plasmon Resonance Property for Effective Visible Light Induced Reductive Catalysis” (DOI: 10.1002/admi.201500632) received a lot of media coverage. Likewise the studies on “Moisture and Oxygen Enhance Conductivity of LiTFSI-Doped Spiro-MeOTAD Hole Transport Layer in Perovskite Solar Cells” (DOI: 10.1002/admi.201600117) by Yabing Qi et al. Both works have been represented in cover images (Figures [1] and [2]). In 2017 we will continue to offer you top-quality articles. This trend is already reflected in the first issue that was published this year. The Special Issue of the Max-Planck Institute of Colloids and Interfaces – Perspectives in Interface Research – which was guest edited by Helmuth Möhwald and covers a wide range of topics on quasi-planar interfaces, multilayers, microcapsules, nanoparticles, and biocomposites. With a steadily increasing number of submissions per year, our team of professional in-house editors, located in Weinheim and Berlin in Germany, and Beijing in China, has also grown and now comprises Peter Gregory (Editor-in-Chief), Prisca Henheik, Yan Li, Ulf Scheffler, Lisa Smith, Anna Troeger, Marc Zastrow, and Bo Weng (Editors). In this context, we are also very happy to announce that our Advisory Board has grown and that the following experts have joined the board: Ariando (National University of Singapore), Charles Ahn (Yale University), Mats Fahlman (Linköping University), Jinlong Gong (Tianjin University), Antoine Kahn (Princeton University), David Kisailus (University of California, Riverside), Maria Antonietta Loi (University of Groningen), and Christof Woell (Karlsruhe Institute of Technology). Our rising profile in the materials science community would not have been possible without the contributions from Advisory Board members, authors, reviewers and readers. Therefore, we would like to take this opportunity to thank all contributors for advice, continuous support, and submissions to the journal. We are looking forward to another year of exciting contributions in this highly interdisciplinary research field and wish you a healthy 2017 and continued success with your work. On behalf of the editorial team,

Laser patterning of vacuum processed small molecular weight organic photovoltaics

In this paper, we report on laser patterned vacuum processed organic solar cells using an infrared ultra short pulse laser. Laser patterning is performed on all layers, electrodes as well as organic layers, to produce fast, reproducible, and precise scribes. The structuring enables monolithically interconnecting several cells to mini-modules. For patterning the silver top electrode, a plasma process is introduced which lowers the ablation threshold and minimizes protrusion-induced shunt formation. Finally, we demonstrate the up-scaling of organic mini-modules to an area of 64cm2 with a geometric fill factor of 94% and a power conversion efficiency on the aperture area of 4.3%.

Silver Iodide Formation in Methyl Ammonium Lead Iodide Perovskite Solar Cells with Silver Top Electrodes

Silver is a low‐cost candidate electrode material for perovskite solar cells. However, in such cells the silver electrodes turn yellow within days of device fabrication. The color change is also accompanied by a dramatic decrease in the power conversion efficiency when compared to otherwise identical devices using gold electrodes. Here, it is shown that the color change results from silver oxidation to silver iodide, due to a reaction with iodine in methyl ammonium lead perovskite. The change in X‐ray diffraction and X‐ray photo­electron spectroscopy is discussed. Exposure to air accelerates corrosion of the Ag electrodes when compared to dry nitrogen gas exposure. However, iodine not reacted with silver is observed by X‐ray photoelectron spectroscopy even for the perovskite solar cell kept in dry nitrogen gas. It is proposed that silver iodide is formed when methyl ammonium iodide migration is facilitated by the small pinholes in the hole transport layer spiro‐MeOTAD.

Screen printed silver top electrode for efficient inverted organic solar cells

The present work is mainly focused on replacement of the vacuum process for top electrode fabrication in organic solar cells. Silver top electrode deposited through solution based screen printing on pre-deposited polymeric thin film. The solution based printing technology provides uniform top electrode without damaging the underlying organic layers. The surface crystallinity and surface morphology of silver top electrode are examined through X-ray diffraction, field-emission scanning electron microscope and atomic force microscope. The purity of silver is examined through X-ray energy dispersive spectroscopy. The top electrode exhibits face centered cubic structure with homogeneous morphology. The sheet resistance of top electrode is found to be 0.06Ω/sq and an average pattern thickness of ∼15μm. The power conversion efficiency is 2.58%. Our work demonstrates that the solution based screen printing is a significant role in the replacement of vacuum process for the fabrication of top electrode in organic solar cells.

Performance improvement of amorphous indium–gallium–zinc oxide ReRAM with SiO2 inserting layer

In this study, the resistive switching performance of amorphous indium–gallium–zinc oxide (a-IGZO) resistive switching random-access memory (ReRAM) was improved by inserting a thin silicon oxide layer between silver (Ag) top electrode and a-IGZO resistive switching layer. Compared with the single a-IGZO layer structure, the SiO2/a-IGZO bi-layer structure exhibits the higher On/Off resistance ratio larger than 103, and the lower operation power using a smaller SET compliance current. In addition, good endurance and excellent retention characteristics were achieved. Furthermore, multilevel resistance states are obtained through adjusting SET compliance current and RESET stop voltage, which shows a promise for high-performance nonvolatile multilevel memory application.

Ultimate form freedom in thin film solar cells by postmanufacture laser-based processing

Thin film photovoltaics can be beneficial for specific applications like building integrated photovoltaics. To fully exploit the differentiator of form freedom, the interconnections in thin film modules can be tuned depending on the required module output. Traditionally, an alternation of coating and scribing steps is applied, determining the form from the start. Here, we present a set of techniques to define the module design from a master substrate with homogeneously coated electroactive layers. By applying subtractive and additive laser-based processes, the size and form of the module are only fixed after the manufacturing of the whole solar cell stack. By laser-induced forward transfer, an isolating dielectric material and a conductive top electrode are deposited in laser ablated scribes to enable the interconnection between two adjacent cells. After optimization of the laser settings for ablation and forward transfer, the optimal annealing time and temperature for the curing of the silver top electrode were determined. The proof of principle was demonstrated by constructing a 4-cell organic solar module of 1.0% efficiency on an area of over 3 cm2 showing the anticipated short-circuit current and open-circuit voltage.