Shaohu Han

All-solution processed polymer light-emitting diode displays.

Adopting the emerging technology of printed electronics in manufacturing novel ultrathin flat panel displays attracts both academic and industrial interests because of the challenge in the device physics and the potential of reducing production costs. Here we produce all-solution processed polymer light-emitting diode displays by solution-depositing the cathode and utilizing a multifunctional buffer layer between the cathode and the organic layers. The use of ink-jetted conducting nanoparticles as the cathode yields high-resolution cathode patterns without any mechanical stress on the organic layers. The buffer layer, which offers the functions of solvent-proof electron injection and proper affinity, is fabricated by mixing the water/alcohol-soluble polymer and a curable epoxy adhesive. Our 1.5-inch polymer light-emitting diode displays are fabricated without any dead pixels or dead lines. The all-solution process eliminates the need for high vacuum for thermal evaporation of the cathode, which paves the way to industrial roll-to-roll manufacturing of flat panel displays.

Novel efficient green electroluminescent conjugated polymers based on fluorene and triarylpyrazoline for light-emitting diodes

A series of novel light-emitting conjugated polymers based on fluorene and triarylpyrazoline were synthesized in good yields through Suzuki coupling reactions. The resulting polymers were characterized by NMR, FT-IR, elemental analysis, DSC, TGA and GPC. These polymers possess excellent thermal stability with glass transition temperatures (Tg) of 80–162 °C and onset decomposition temperatures (Td) of 376–387 °C. Cyclic voltammetry studies revealed that these polymers have good hole and electron transporting properties with LUMO energy levels of −2.97 to −2.98 eV and HOMO energy levels of −5.71 to −5.81 eV. All the polymers emit green fluorescence with very high photoluminescence (PL) quantum yields of 45–59%. Polymer light-emitting diodes (PLEDs) with the configuration ITO/PEDOT/polymer/Ba/Al were fabricated. All these devices showed bright green emission peaking at 494–500 nm with high maximum external quantum efficiencies of 0.6–2.53% and low turn-on bias voltages. The good light-emitting properties indicate that these polymers are new and promising candidates for electroluminescent materials that can be used to fabricate efficient polymer light-emitting diodes.

In situ patterning of microgrooves via inkjet etching for a solution-processed OLED display

Inkjet-printing a solvent onto an insulating polymer layer is employed to in situ build microgrooves as bank structures in the application of a solution-processed OLED display. The inkjet-etching process not only eliminates photolithographys shadow mask and photo exposure, but is also capable of constructing bank structures on any functional layer. The orthogonal solubility between the CYtop polymer and the organic layer avoids any solvent erosion. A pixelated display is successfully fabricated by inkjet-printing a blue-emitting polymer onto inkjet-etched CYtop microgrooves with a pixel resolution of 140 lines per inch. Forming a bank structure in situ on any layer as needed offers more choices to design a new panel structure, device architecture, and deposition methods.

Saturated red light emitting polymers and devices

A series of saturated red emission copolymers, polyfluorene copolymers (PFO-DBT), were synthesized and characterized. The saturated red EL emission from the copolymer peaking at about 677 nm and electroluminescence (EL) efficiency of 1.4% based on simple device structure of ITO/PEDOT/PFO-DBT/Ba/Al, were achieved. The operation mechanism of the device was discussed and it was found that hole carrier injection is the major obstacle for improving EL efficiency and EL stability. To overcome such problem, we utilized MEH-PPV which has low HOMO level blended with the PFO-DBT copolymer to improve EL efficiency to 1.7%. Simultaneously, the EL emission lifetime of the device with PFO-DBT:MEH-PPV (50:50) blended polymer extended to 2000hrs. Monochrome passive red emission displays with the blended polymer were fabricated, and exhibited excellent pictures.

P‐117: Efficiently Saturated Red Emission Polymers and Matrix Display

Synthesized were novel dioctylfluorene (DOF) and benzothiadiazole (DBT) copolymers having various contents of DBT and yielding pure red emission. Based on the copolymer only with 5% of DBT as the emitter, the external quantum efficiency is over 2.0% from the device whose structure is ITO/PVK/DOF-DBT5/Ba/Al. The efficiency can be further improved by over 4.0% using the blend polymer of P-PPV and DOF-DBT(5%) on energy transfer mechanism. The red-emitting copolymer was utilized to fabricate a matrix display which showed wonderful pictures, demonstrating that the new red efficient copolymer could be a promising candidate for practical applications.