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Organic Light-Emitting Diode (OLED) and Polymer Light-Emitting Diode (PLED) are light-emitting device technologies with high promise and potential. It is a modern display lighting and lighting technology that converts electrical energy into light energy based on the principle of electroluminescence (EL) in organic materials. The key point is the structural design of the organic material and the matching of the function of each layer of the device. The selected material has a direct impact on the key parameters of OLED / PLED device, including luminous efficacy, luminous color spectrum, lifetime, power consumption, stability, and color purity.
In these devices, the key layers include:
Fig. 1 Device structure of a typical OLED[1].
PLEDs are typically solution processed / printed by polymeric materials, while Small Molecule OLEDs (SM-OLEDs) are vacuum vaporized by small molecules with low molecular weight and precisely designed structure. Organic molecules and polymers each have their own advantages, and the materials can be chosen based on the needs of the application (e.g., color, resolution, cost, stability, processing, etc.).
Alfa Chemistry provides a broad spectrum of high-purity, advanced OLED materials, including small-molecule light-emitting materials and dopants, light-emitting polymers, phosphorescent and fluorescent host materials, inorganic and organic electron transport (hole-blocking) materials, hole-injection, and hole-transport materials.
SM-OLED materials refer to organic small molecules with small molecular weight (usually in the hundreds or thousands) that can be coated into films through vacuum evaporation and other methods and are commonly used in OLED devices. They are usually coated into films by vacuum evaporation, which is the mainstream method of mass production at present. As the molecular weight is small, it is easy to purify, and its luminous efficiency and thermal stability are relatively high. In addition, compared with polymer materials, small molecule materials have higher luminous efficiency, brightness, and color purity. SM-OLED materials have been used in the market for OLED display devices such as flat panel displays (FPDs) and solid-state lighting (SSL).
Fig. 2 Examples of small molecule organic materials for OLED[2].
The small molecule OLED material portfolio of Alfa Chemistry is high-purity, performance-optimized chemicals, specifically developed for next-generation OLED and PLED devices. We have divided SM-OLED materials into the following subcategories. Click here to learn more.
Host Materials
Host materials are used to host the luminescent agent (dopant/emissive molecule) in the emissive layer. Their main role is to assist in transferring the charge carrier (electron or hole) to the luminescent agent to achieve high-efficiency energy transfer, while at the same time suppressing the quenching between the luminescent agent molecules and not allowing the triplet energy to transfer back to the host, to ensure device efficiency and lifetime.
Dopant Materials
These materials are responsible for the actual luminescence (emissive) portion. Dopants play a luminescent role, emitting the energy from electron/hole recombination as visible light through mechanisms such as fluorescence, phosphorescence, or thermally activated delayed fluorescence (TADF).
MR-TADF Materials
Multiple-Resonance TADF (MR-TADF) is a special structural design strategy for TADF. The way to achieve it is to introduce the electron donor and electron acceptor atoms (such as B, N, and O) of the molecule by resonance and limit the spread of the HOMO and LUMO atoms so as to reduce the ∆E_ST as much as possible and narrow the emission spectrum. The structure produces high color purity, a small Stokes shift, high luminous efficiency, and low efficiency roll-off.
Charge Transport Layer Materials
The material itself does not emit light, but it plays a decisive role in the device. It determines the injection efficiency, transport balance, and recombination sites of electrons and holes, thus affecting the exciton density, device efficiency, lifetime, and color purity of the light-emitting layer.
Purchasing SM-OLED materials from us not only ensures reliable supply and consistent specifications but also provides technical support, which will accelerate innovation and speed up the time to market of high-performance optoelectronic products.
PLED materials are a hot spot for research in display devices in recent years. It has received widespread attention because of its easy processing, mechanical flexibility, large-area manufacturability, and other characteristics. It is a type of OLED whose light-emitting layer is made of polymer materials. Its structure is generally composed of an anode (usually ITO), a light-emitting layer (polymer material), and a cathode (usually aluminum or magnesium). Under the action of voltage, electrons and holes in the polymer layer are combined to generate photons and then emit light.
Fig. 3 Schematic structure of a single-layer PLED[3].
PLED materials are mainly divided into the following categories:
In order to design an OLED/PLED device with excellent performance, good stability, and high color purity, here are some guidelines for matching and selection.
Fig. 4 Comparison of SM-LED and PLED.[4].
Requirements: Are you looking for the highest efficiency (e.g., HQE, EQE, IQE), extreme color purity (especially blue/red), long lifetime, or low cost/large-area processing?
1. Luminescence Mechanism
If cost/fabrication is easy, fluorescent emitters still have market;
If high efficiency is required, phosphor or TADF/MR-TADF can be considered;
If blue or deep blue is required, and color purity is required, high-energy host and MR-TADF are good directions.
2. Energy Level and Matching
Host's HOMO/LUMO should be matched with HTL and ETL to minimize charge injection/transmission loss;
Luminol (triplet/single-line) energy level should be carefully matched with the triplet energy of the host to avoid energy reflux or triplet burst.
3. Thermal and Morphological Stability
High Tg and Td for Host and luminophores at high operating temperatures and long-time illumination;
Rigid molecular structure reduces non-radiative losses;
For solution processing (especially PLED or some SM-OLED solution stacked structures), solvent tolerance of the material and interfacial stability of the film are very critical.
4. Purity and Ease of Processing
Vaporized materials need to be finely purified to reduce impurities and residual solvents;
Polymer luminescent materials need to have good solubility and printability;
MR-TADF materials tend to be more complex to synthesize, so the cost/volume production capacity needs to be evaluated.
Contact our team today to discuss specifications, request samples or receive a tailored quotation for your project needs.
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