Resistive switching in transition metal oxides

Functionalized acenes and heteroacenes for organic electronics.

A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

Energy‐Level Alignment at Organic/Metal and Organic/Organic Interfaces

This article summarises the industrial applications of poly-(3,4-ethylenedioxythiophene)
				(PEDT, PEDOT). The basic chemical and physical properties of PEDT are discussed to outline the fundamentals which lead to PEDT as a highly valuable electric and electronic material. PEDT applications are reviewed depending on the two different ways of preparation: in situ polymerisation of the monomer, usually carried out by the user, and applying the prefabricated polymer in the form of its water-based complex with poly(styrene sulfonic acid). Several applications like antistatic coatings, cathodes in capacitors, through-hole plating, OLED's, OFET's, photovoltaics, and electrochromic applications are discussed in detail.

Scientific importance, properties and growing applications of poly(3,4-ethylenedioxythiophene)

On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment

The conductivity of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film can be enhanced by more than two orders of magnitude by adding a compound with two or more polar groups, such as ethylene glycol, meso-erythritol (1,2,3,4-tetrahydroxybutane), or 2-nitroenthanol, to an aqueous solution of PEDOT:PSS. The mechanism for this conductivity enhancement is studied, and a new mechanism proposed. Raman spectroscopy indicates an effect of the liquid additive on the chemical structure of the PEDOT chains, which suggests a conformational change of PEDOT chains in the film. Both coil and linear conformations or an expanded-coil conformation of the PEDOT chains may be present in the untreated PEDOT:PSS film, and the linear or expanded-coil conformations may become dominant in the treated PEDOT:PSS film. This conformational change results in the enhancement of charge-carrier mobility in the film and leads to an enhanced conductivity. The high-conductivity PEDOT:PSS film is ideal as an electrode for polymer optoelectronic devices. Polymer light-emitting diodes and photovoltaic cells fabricated using such high-conductivity PEDOT:PSS films as the anode exhibit a high performance, close to that obtained using indium tin oxide as the anode.

High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices†

The external electroluminescence (EL) quantum efficiency (QEEL) of a polymer light-emitting diode (PLED) can be affected by the following four factors: a) charge balance, b) the efficiency of producing singlet excitons, c) photoluminescence quantum efficiency (QEPL), and d) the output coupling effect. The QEPL can approach unity and the efficiency of producing singlet excitons can be high in long-chain polymers. Therefore, the dominating factor for achieving high efficiency for a given polymer is the balance and confinement of electrons and holes. Unfortunately, most conjugated polymers have unbalanced charge-transport properties as the hole mobility is much larger than the electron mobility. In this manuscript, we report a general method to significantly increase the efficiency of PLEDs by controlling the charge injection and distribution through material processing and interface engineering in the device. By blending high-bandgap and low-bandgap polymers in proper ratios, we were able to introduce charge traps in the light-emitting polymer (LEP) layer. Similarly, by introducing an electron-injection/hole-blocking layer, we were able to enhance the minority carrier (electron) injection and confine holes to the emissive layer. Efficient and balanced charge injection, as well as charge confinement, are attained simultaneously, and as a result high-efficiency devices can be achieved. This is a simple yet powerful concept in enhancing the overall efficiency of PLEDs. To illustrated our concept, we have blended 0.25–2 % of poly[2-methoxy-5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with poly(9,9-dioctylfluorene) (PFO) as the active polymer layer for PLEDs. A Cs2CO3 electron-injection (and hole-blocking) layer is used at the cathode interface. The emission from the device covers colors from white to yellow, depending on the blend ratio, with the highest peak efficiency being 16 lm W. To the best of our knowledge, this is the highest reported efficiency for a white-light emitting PLED. There are several benefits to using a polymer blend: 1) the low-bandgap LEP behaves as a dopant for energy transfer from the higher-bandgap LEP, 2) the low-bandgap LEP behaves as a charge-trapping site to trap (and confine) the injected charges, which is particularly important in the low-voltage regime where only one type of charge is often present, and 3) the trapped electrons in the low-bandgap LEP will eventually help with the injection of holes and lead to self-balanced charge injection. When this LEP blend system is coupled with an electron-injection (and hole-blocking) layer of Ca(acac)2 [4] (acac: acetylacetonate) or Cs2CO3 [5] at the cathode interface, holes are blocked within the LEP layer as well. As a result, both electrons and holes are effectively confined in the LEP layer rather than being extracted directly at the electrodes. Hence, efficient recombination occurs due to the overlapping distribution of electrons and holes (through formation of excitons). All of these factors can help to increase the efficiency of PLED devices. The schematic profile of the energy structure is shown in Figure 1.

Achieving High-Efficiency Polymer White-Light-Emitting Devices

Two-terminal electrical bistable devices have been fabricated using a sandwich structure of organic/metal/organic as the active medium, sandwiched between two external electrodes. The nonvolatile electrical bistability of these devices can be controlled using a positive and a negative electrical bias alternatively. A forward bias may switch the device to a high-conductance state, while a reverse bias is required to restore it to a low-conductance state. In this letter, a model to explain this electrical bistability is proposed. It is found that the bistability is very sensitive to the nanostructure of the middle metal layer. For obtaining the devices with well-controlled bistability, the middle metal layer is incorporated with metal nanoclusters separated by thin oxide layers. These nanoclusters behave as the charge storage elements, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. This mechanism is supported by the experimental data obtained from UV–visible ...

Nonvolatile electrical bistability of organic/metal-nanocluster/organic system

Copper (Cu) migration into semiconductor materials like silicon is a well-known and troublesome phenomenon often causing adverse effect on devices. Generally a diffusion barrier layer is added to prevent Cu metallization. We demonstrate an organic nonvolatile memory device by controlling the Cu-ion (Cu+) concentration within the organic layer. When the Cu+ concentration is high enough, the device exhibits a high conductive state due to the metallization effect. When the Cu+ concentration is low, the device displays a low conductance state. These two states differ in their electrical conductivity by more than seven orders of magnitude and can be precisely switched by controlling the Cu+ concentration through the application of external biases. The retention time of both states can be more than several months, and the device is promising for flash memory application. Discussions about the device operation mechanism are provided.

/pdf/organic-nonvolatile-memory-by-controlling-the-dynamic-copper-3esmt3g5dv.pdf

Qianfei Xu

Papers

On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment

High-Conductivity Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Film and Its Application in Polymer Optoelectronic Devices†

Achieving High-Efficiency Polymer White-Light-Emitting Devices

Nonvolatile electrical bistability of organic/metal-nanocluster/organic system

Organic nonvolatile memory by controlling the dynamic copper-ion concentration within organic layer