Realization of a blue‐light‐emitting device using poly(p‐phenylene)

Abstract

The use of light-emitting diodes (LEDs) continues to increase dramatically, for example in color computer screens based on flat LED boards which are intended to replace the large and expensive cathode-ray tubes. In the past, it has proved difficult to economically extend the emission spectra of the LEDs into the blue spectral region.The story of the LED goes back to 1907,L'I and in the last 35 years much effort has been invested in the study of inorganic semiconductors e.g. GaN, ZnS, ZnSe and S i c in order to produce an effective blue LED. However, large scale applications have not been practicable due to the problems in fabrication and the rather low luminescence efficiency. Therefore, the use of alternative materials was proposed[21 in order to extend the spectral region into the blue.Organic materials have always been considered for use in electroluminescent devices,[31 but up to now they have not been widely used except for applications in scintillation detectors. Only recently has there been a noticable effort in electroluminescent device fabrication with organic laye r~. [~. ' 1 The observed transfer function between the current input and luminescence output of organic materials is linear, which allows optocouplers without any distortion to be devised. This feature cannot be provided by existing optocoupling devices. A blue light-emitting electroluminescent device, based on low-molecular-weight organic materials with a substantial efficiency was presented recently.I6] A serious disadvantage of devices consisting of organic materials of rather low molecular weight is the tendency of the materials to recrystallize (initiated by the heat produced in the device), which leads to a drastic decrease in quantum efficiency.16] Intensive research activities on the physical properties and synthesis of conjugated polymers[71 have shown these materials to be promising candidates for applications in stable optoelectronic devices. The first encouraging results on LEDs based on semiconducting polymers were reported by Burroughes et al.[*l and confirmed by Braun et al.'91 These devices emitted in the yellowish ( x 600 nm) sprectral range.In the search for new materials for blue LEDs and linear optocouplers, we have investigated the polymer polybphenylene) (PPP, see Fig.

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

“…PHP can be considered as a model substance for phenylene-based materials 8 and is used to build stable blue-emitting OLED's. [2][3][4]9 Due to its well-defined conjugation length and chemical structure, PHP exhibits well-resolved photoinduced absorption ͑PA͒ features that can be assigned to polaron-, triplet-, and singlet-state absorption. This allows us to optically address the exciton dissociation and polaron recombination dynamics in a real device structure with femtosecond time resolution.…”

Solid-state-concentration effects on the optical absorption and emission of poly(p-phenylene vinylene)-related materials

“…2 Polymer-based organic LED's were discovered by Burroughes et al some years later and have stimulated a new wave of interest in this field. 3 Polymer devices have now been demonstrated with internal quantum efficiencies of up to 4%, 4 operating voltages below 5 V, emission wavelengths throughout the visible spectrum, [3][4][5][6][7] and operating lifetimes beyond 1200 h. 8 The simplest organic LED's consist of a thin, light-emitting organic film sandwiched between two metal electrodes. Even in these structures there is a need for a better understanding of the mechanisms of operation and methods to control the electrical and optical properties of the organic film to optimize charge injection, charge transport, charge recombination, and light-emission processes.…”

Structural, morphological and spectroelectrochemical characterization of poly (2-ethyl aniline)

“…Conducting organic polymers have shown great potential for many applications, including rechargeable batteries, corrosion protection, light emitting diodes, molecular sensors, electrochromic devices and gas separation membranes [1][2][3][4][5][6] . For these applications, the polymers must be highly processable and chemically stable for long periods of time.…”