Doubly Boron-Doped TADF Emitters Decorated with ortho-Donor Groups for Highly Efficient Green to Red OLEDs.

Doubly boron-doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10-diboraanthracene (DBA) acceptor decorated with ortho-donor groups (Cz2oDBA, 2; BuCz2oDBA, 3; DMAC2oDBA, 4) are prepared to realize high-efficiency green-to-red organic light-emitting diodes (OLEDs). X-ray diffraction analyses of 2 and 4 reveal the symmetrical and highly twisted ortho-donor-acceptor-donor (D-A-D) structure of the emitters. The twisted conformation leads to a very small energy splitting (ΔEST <0.08 eV) between the excited singlet and triplet states that gives rise to strong TADF, as supported by theoretical studies. Depending on the strength of the donor moieties, the emission color is fine-tuned in the visible region from green (2) to yellow (3) to red (4). Carbazole-containing 2 and 3 exhibit high photoluminescence quantum yields (PLQYs) approaching 100 %, whereas DMAC-substituted 4 is moderately emissive (PLQY=44 %) in a doped host film. Highly efficient green-to-red TADF-OLEDs are realized with the proposed ortho-D-A-D compounds as emitters. The green and yellow OLEDs incorporating Cz2oDBA (2) and BuCz2oDBA (3) emitters exhibit high external quantum efficiencies (EQEs) of 26.6 % and 21.6 %, respectively. In particular, the green device shows an excellent power efficiency above 100 lm W-1 . A red OLED fabricated with a DMAC2oDBA (4) emitter exhibits a maximum EQE of 10.1 % with an electroluminescence peak at 615 nm.

Two-Color Pixel Patterning for High-Resolution Organic Light-Emitting Displays Using Photolithography.

Nowadays, the display industry is endeavoring to develop technology to provide large-area organic light-emitting diode (OLED) display panels with 8K or higher resolution. Although the selective deposition of organic molecules through shadow masks has proven to be the method of choice for mobile panels, it may not be so when independently defined high-resolution pixels are to be manufactured on a large substrate. This technical challenge motivated us to adopt the well-established photolithographic protocol to the OLED pixel patterning. In this study, we demonstrate the two-color OLED pixels integrated on a single substrate using a negative-tone highly fluorinated photoresist (PR) and fluorous solvents. Preliminary experiments were performed to examine the probable damaging effects of the developing and stripping processes upon a hole-transporting layer (HTL). No significant deterioration in the efficiency of the develop-processed device was observed. Efficiency of the device after lift-off was up to 72% relative to that of the reference device with no significant change in operating voltage. The procedure was repeated to successfully obtain two-color pixel arrays. Furthermore, the patterning of 15 µm green pixels was accomplished. It is expected that photolithography can provide a useful tool for the production of high-resolution large OLED displays in the near future.