Top-emitting Polymer Light-emitting Diodes Research Articles

Full-solution processed, flexible, top-emitting polymer light-emitting diodes based on printed Ag electrodes

Full-solution processed, flexible, top-emitting polymer light-emitting diodes are fabricated by using low-cost and high-quality printed Ag electrodes.

Integrated semiconductor optoelectronic devices for real-time and indicator-free detection of aqueous nitric oxide

A real-time and indicator-free sensor specific to nitric oxide (NO) is realized for the first time by integrating a sensing hydrogel film, a top-emitting polymer light-emitting diode (PLED), and a silicon photodetector. The top-emitting PLED is utilized to excite the sensing film specific to NO, and the photoluminescence of the sensing film is transformed into electric signal by the photodetector. The influence of the excitation light on the out-put photocurrent of the photodetector is diminished by two delicately selected organic filters based on their absorption spectra. Lead phthalocyanine is deposited on a top-emitting PLED as a filter for generating an excitation light without overlapping the emission maximum of the sensing hydrogel film. Poly(3-hexylthiophene) is placed in front of the photodetector as another filter to remove the excitation light. This sensor demonstrated a fast photocurrent response to NO with response time within 5 min.

A Study of Semitransparent Cathodes on the Performance of Top-Emitting Polymer Light-Emitting Diodes

This work reports the influence of semitransparent cathodes, which were made of Ca or Al covered with a thin layer of Ag, on the performance of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV)-based top-emitting polymer light-emitting diodes (T-PLEDs). The physical properties of the semitransparent cathodes alter the optical microcavity of T-PLEDs and adjust the output characteristics of the electroluminescence (EL). The bright, red-emissive, MEH-PPV-based T-PLED, with Ca(10 nm)/Ag(20 nm) as the semitransparent cathode, exhibited 3.6 cd/A, 38.7 nm, and (x = 0.67, y = 0.33) for the luminous efficiency, full-width at half-maximum of the EL, and Commission International de I'Eclairage coordinate, respectively. The favorable performance can be attributed to the formation of an appropriate microcavity structure, which results in spatial redistribution and enhances the out-coupling of EL emission in the direction of the surface normal.

Light-emitting polymer space-charge-limited transistor

Polymer light-emitting transistor is realized by vertically stacking a top-emitting polymer light-emitting diode on a polymer space-charge-limited transistor. The transistor modulates the current flow of the light-emitting diode by the metal-grid base voltage. The active semiconductor of the transistor is poly(3-hexylthiophene). Yellow poly(para-phenylene vinylene) derivative is used as the yellow emitting material. As the cathode is fixed at −12 V and the grid base voltage varies from 0.9 to −0.9 V the light emission is turned on and off with on luminance up to 1208 cd/m2. The current efficiency of the light-emitting transistor is 10 cd/A.

Efficient Top-Emitting Polymer Light-Emitting Diodes UsingChromium as Anode

We demonstrate a high efficiency top-emitting polymer light-emittingdiode (TPLED) with chromium (Cr) taking as the anode. The TPLEDstructure is Cr/poly-3, 4-ethylenedioxythiophene (PEDOT:PSS)/poly[2-(4-3′,7′-dimethyloctyloxy)-phenyl]-p-phenylenevinylene)(P-PPV)/Ba/Ag. The Cr (100 nm) anode is prepared by sputter-depositingin a vacuum chamber. It is found that the device emissive propertiesare affected dramatically by the thickness of both PEDOT:PSS and the Agcathode. Optimized thicknesses of PEDOT:PSS and Ag layer are 60 nm and15 nm, respectively. The diode exhibits excellent electroluminescence(EL) properties, such as a turn-on voltage of 3.32 V, luminousefficiency of 4.41 cd/A and luminance of 6989 cd/m2 at drivingvoltage of about 9 V.

Process Technology for High-Resolution AM-PLED Displays on Flexible Metal-Foil Substrates

The first successful integration of a polysilicon thin-film transistor (TFT) backplane with polymer light-emitting diodes (PLEDs) onto a flexible stainless steel foil is described, and a high-resolution (230 dots/in.) monochrome active-matrix polymer light-emitting diode (AM-PLED) display is demonstrated. The process technology required to implement this high-resolution AM-PLED display onto a flexible metal-foil substrate is discussed. This technology primarily consists of the preparation of flexible metal foil, fabrication of the active matrix polysilicon TFT backplane, and integration with top-emitting PLEDs.

Self-assembled monolayer-modified Ag anode for top-emitting polymer light-emitting diodes

A self-assembled monolayer (SAM), 4-fluorothiophenol (4-FTP), is employed to modify the Ag anode of a top-emitting polymer light-emitting diode (T-PLED) to enhance the hole injection and the performance of a T-PLED device. The results show that the reflectivity of the Ag anode does not decrease due to the formation of a SAM. A brightness of 68981cd∕m2 and a luminous efficiency of 10.3cd∕A have been achieved for the 4-FTP-modified device. The improved performance is attributed to the work function increase of the Ag/4-FTP anode due to the presence of fluorine atoms at the outer surface of the modified anode.

Process Technology for High-Resolution AM-PLED Displays on Flexible Metal Foil Substrates

The first successful integration of poly-Si thin-film- transistor (poly-Si TFT) backplane with polymer light-emitting diodes (PLEDs) onto a flexible stainless-steel foil is described, and a high-resolution (230 DPI) monochrome active- matrix polymer light-emitting diode (AM-PLED) display is demonstrated. The process technology required to implement this high-resolution AM-PLED display onto a flexible metal foil substrate is discussed. This technology primarily consists of the preparation of flexible metal foils, fabrication of the poly-Si TFT backplane, and integration with top-emitting PLEDs.

Top-emitting polymer light-emitting diodes with environmentally stable cathodes

We report the demonstration of polymer-based top-emitting diodes that employed environmentally stable cathode materials. The device employed an emissive polymer blend that we reported previously [Deng et al. Appl. Phys. Lett. 84, 3522 (2004)]. By constructing a semitransparent cathode using the stable metals Al and Ag, bright light emission through the top cathode was achieved. An index-matching overlayer deposited by spin coating was shown to enhance the transmission efficiency through the top electrode. Microcavity effects were observed for the device by replacing the indium tin oxide anode with Au, resulting in wavelength tunability of the device.

High-efficiency inverted top-emitting polymer light-emitting diodes

A major challenge to inverted top-emitting polymer light-emitting diodes (ITEPLEDs) is to prepare a reflective bottom cathode capable of effectively injecting electrons. Reported in this letter is the creation of an efficient electron injection layer (EIL) by using environment-friendly alcohol-/water-soluble aminoalkyl-substituted conjugated quanternized polyfluorene copolymers containing 0.5%mol of benzothiadiazole to reduce the electron injection barrier between the high-work-function Al reflective bottom cathode and the light-emitting layer. The inverted top-emitting devices exhibit superior electrical characteristics with maximal quantum and luminance efficiencies of 2.71% and 1.6cd∕A respectively, at an operating voltage of 13.3V by employing poly[2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene] as a light-emitting polymer. The utilization of water/alcohol soluble conjugated polyelectrolyte/Al bilayer bottom cathode offers an important advantage for avoiding intermixing between the emitting layer and the EIL for solution-processable ITEPLEDs.