Organic Light-emitting Polymer Research Articles

Flexible nanogap polymer light-emitting diodes fabricated via adhesion lithography (a-Lith)

We report the development of coplanar green colour organic light-emitting diodes (OLEDs) based on asymmetric nanogap electrodes fabricated on different substrates including glass and plastic. Using adhesion lithography (a-Lith) we pattern Al and Au layers acting as the cathode and anode electrodes, respectively, separated by an inter-electrode distance of <15 nm with an aspect ratio of up to 106. Spin-coating the organic light-emitting polymer poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) on top of the asymmetric Al–Au nanogap electrodes results in green light-emitting nanogap OLEDs with promising operating characteristics. We show that the scaling of the OLED’s width from 4 to 200 mm can substantially improve the light output of the device without any adverse effects on the manufacturing yield. Furthermore, it is found that the light-emitting properties in the nanogap area differ from the bulk organic film, an effect attributed to confinement of the conjugated polymer chains in the nanogap channel. These results render a-Lith particularly attractive for low cost facile fabrication of nanoscale light-emitting sources and arrays on different substrates of arbitrary size.

Electrically Injected Hybrid Organic/Inorganic III-Nitride White Light-Emitting Diodes with Nonradiative Förster Resonance Energy Transfer

An electrically injected hybrid organic/inorganic III-nitride white light-emitting diode (LED) has been fabricated by using a two-dimensional (2D) microhole array structure. The hybrid LED geometry significantly enhances proximity between the inorganic active-region and the down-converting yellow organic light-emitting polymers (OLEPs), enabling the near-field nonradiative Forster resonance energy transfer (FRET) process with high efficiency while retaining excellent electrical characteristics of an unpatterned planar LED. A reduction in the recombination lifetime in the InGaN/GaN blue active region has been observed with the hybrid device, confirming the nonradiative FRET process occurring between the InGaN/GaN blue active region and the yellow organic polymer. This results in a typical FRET efficiency of 16.7%, where the FRET interaction area accounts for approximately 0.64% of the remaining blue-emitting inorganic LED, but enhancing total device efficiency. An optimized white-light EL emission is achie...

Spectroscopic Study of Organic Light‐Emitting Polymers: A Review

AbstractIn this review paper, we theoretically investigate the optical properties of the organic light‐emitting polymer (OLEP). Despite of its enormous size, OLEP is described well by the oligomer model because of the imperfect backbone structure. By using the molecular exciton theory, we calculate the energy level of S1 states and Huang‐Rhys factor of oligomer which decrease with its chain length. The spectral profiles for oligomer thus can be readily calculated and used to explain the absorption and PL for OLEP in dilute solution with a chain length distribution described by a Gaussian function. Moreover we show that the luminescence of OLEP in high concentration solution as well as thin film is mainly contributed by the interchain states. In the ultrafast time‐resolved PL spectrum, we propose a model in which the dynamic processes such as energy transfer, charge transfer, and vibrational relaxation are treated in an equal‐footing manner, and find that in the high energy region the states in a thin film of OLEP is dominated by the intrachain species. In addition, we discuss the nonradiative transitions occurring in OLEP.

Hybrid inorganic/organic microstructured light-emitting diodes produced using photocurable polymer blends

Light-emitting diodes (LEDs) in the form of a one-dimensional array of microstripes emitting at 370nm were fabricated from AlInGaN inorganic semiconductor. These microlight sources were then used to “directly write” microstructures in photocurable blends of organic light-emitting polymers (LEPs) spin coated onto the LED surface. In this way, thin microstripes of LEP as narrow as 50μm have been fabricated and integrated with the micro-LEDs. These “self-aligned” polymer microstripes serve as wavelength downconverters under further excitation by the UV micro-LEDs, producing hybrid inorganic/organic microstructured LEDs.

Multilevel, Room-Temperature Nanoimprint Lithography for Conjugated Polymer-Based Photonics

We demonstrate the multilevel patterning of organic light-emitting polymers by room-temperature nanoimprint lithography (RT-NIL), which is impossible to obtain by conventional hot embossing. In particular, we realize one- and two-dimensional photonic crystals with 500 nm periodic features and investigate the changes in the optical properties (luminescence and quantum yield) of the organic active layer. An increase of the quantum yield by 2.4% for the patterned film with respect to the untextured one and the enhancement of the output light emitted at a particular angle (Theta = 69 degrees) are observed for gratings whose Bragg periodicity matched the emission wavelength of the polymer. The employment of RT-NIL to pattern polymer semiconductors without degradation of their optical properties represents a strategic route for the realization of novel nanopatterned optoelectronic devices.