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

This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

The electroluminescence of organic materials

A multicolor organic light emitting device employs vertically stacked layers of double heterostructure devices which are fabricated from organic compounds. The vertical stacked structure is formed on a glass base having a transparent coating of ITO or similar metal to provide a substrate. Deposited on the substrate is the vertical stacked arrangement of three double heterostructure devices, each fabricated from a suitable organic material. Stacking is implemented such that the double heterostructure with the longest wavelength is on the top of the stack. This constitutes the device emitting red light on the top with the device having the shortest wavelength, namely, the device emitting blue light, on the bottom of the stack. Located between the red and blue device structures is the green device structure. The devices are configured as stacked to provide a staircase profile whereby each device is separated from the other by a thin transparent conductive contact layer to enable light emanating from each of the devices to pass through the semitransparent contacts and through the lower device structures while further enabling each of the devices to receive a selective bias. The devices are substantially transparent when de-energized, making them useful for heads-up display applications.

Transparent contacts for organic devices

A light emitting device (100) including a pixel having a substantially transparent anode (111), a hole transporting layer (112) over the anode, an emission layer (113) over the hole transporting layer, a blocking layer (114) over the emission layer, an electron transporting layer (115) over the blocking layer and a cathode (117) in electrical contact with the electron transporting layer.

Structure for high efficiency electroluminescent device

Provided is an organic electroluminescence device having high luminous efficiency, high heat resistance and an extremely long lifetime. The organic electroluminescence device of the present invention includes an organic thin film layer composed of one or more layers containing at least a light emitting layer is interposed between a cathode and an anode. The light emitting layer includes a compound containing a condensed ring and a luminescent metal complex capable of emitting light having a red-based color. It is preferable that the compound containing a condensed ring includes a host material, while the luminescent metal complex capable of emitting light having a red-based color includes a phosphorescent dopant.

Organic Electroluminescent Device

Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct‐current (dc) driving field. Here we report the fabrication of symmetrically configured alternating‐current (ac) light‐emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states.

Alternating‐current light‐emitting devices based on conjugated polymers

Light-emitting bipolar devices (10) consist of a light emitter (15) formed from an electroluminescent organic light-emitting material in contact with an insulating material. The light emitter (15) is in contact with two electrodes (12, 18) that are maintained in spaced-apart relation with each other. The light emitter (15) can be formed as an integral mixture of light-emitting materials and insulating materials or as separate layers of light-emitting and insulating materials. The devices operate with AC voltage (24) of less than twenty-four volts and in some instances at less than five volts. Under AC driving, the devices produce modulated light output that can be frequency or amplitude modulated. Under DC driving, the devices operate in both forward and reverse bias.

Bipolar electroluminescent device

: Symmetrically configured AC light emitting (SCALE) devices based on conjugated polymers utilizing indium tin oxide (ITO) and aluminum as electrodes have been demonstrated recently Here we report the fabrication of SCALE devices using a more stable high work function metal, such as gold, as a charge (both electron and hole) injection electrode Also, a variation of such devices in which the electroluminescent polymer, instead of being separated from the insulating polymer, is dispersed in the insulating polymer to form a unified emitter insulator, is reported These devices emit light in both forward and reverse DC bias with symmetric current voltage characteristics Under low frequency AC (sinusoidal) driving voltage, light pulses with double the driving frequency are observed A model is proposed to account for the device operation

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA305230&Location=U2&doc=GetTRDoc.pdf

Optical and Photonic Applications of Electroactive and Conducting Polymers.

We report the fabrication and properties of three-, four-, and five-layer electroluminescent devices fabricated from light emissive N-based heterocyclic novel polymeric derivatives of PPP and PPV with which they are isoelectronic. They include poly(pyridine vinylene), (PPyV), and poly(2,5-dihexadecanoxy phenylene vinylene pyridyl vinylene), (PPV.PPyV). Some of the devices operate in both forward and reverse bias modes thus enabling operation in an ac mode. One type of device has the general construction: M/I/polymer/I/ITO where M equals Cu or Al, I equals polyaniline (emeraldine base, EB) or poly(3-hexylthiophene), (P3HT), and polymer equals PPV.PPyV. Under low frequency ac (sinusoidal) driving, light pulses with twice the driving frequency were observed in a device where M equals Al or Cu, I equals EB and polymer equals PPV.PPyV; and in a device where M equals Al, I equals P3HT and polymer equals PPV.PPyV. In the latter device the electroluminescence spectrum in the reverse bias mode differed from that in the forward bias mode. It was also shown that blends of PPyV in Nylon 6,6 exhibit a lower operating voltage than the pure polymer.

Novel light-emitting diodes involving heterocyclic aromatic conjugated polymers

We present novel light-emitting devices based on several pyridine-containing conjugated polymers and copolymers in various device configurations. The high electron affinity of pyridine-based polymers improves stability and electron transport properties of the polymers and enables the use of relatively stable metals such as Al as electron injecting contacts. Bilayer devices utilizing poly(9-vinyl carbazole) (PVK) as a hole-transporting/electron-blocking polymer show dramatically improved efficiency and brightness as compared to single layer devices. This is attributed to charge confinement and exciplex emission at the PVK/emitting polymer interface. The incorporation of conducting polyaniline network electrode into PVK reduces the device turn-on voltage significantly while maintaining the high efficiency. Two novel device configurations that enable the use of high work function metals as electrodes are pointed out.

/pdf/novel-light-emitting-devices-based-on-pyridine-containing-185ut8lhib.pdf

D. D. Gebler

Papers

Alternating‐current light‐emitting devices based on conjugated polymers

Bipolar electroluminescent device

Optical and Photonic Applications of Electroactive and Conducting Polymers.

Novel light-emitting diodes involving heterocyclic aromatic conjugated polymers

Novel light-emitting devices based on pyridine-containing conjugated polymers