No abstract

Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin-orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. An extremely fast exciton lifetime of 750 ns was realized in a donor-acceptor-type molecular structure without heavy metal elements. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance.

Organic light-emitting diodes utilizing thermally activated delayed fluorescence is a potential solution for achieving stable blue devices. Sky-blue devices (CIEy < 0.4) with high stability and high external quantum efficiency (>15%) at 1000 cd m−2 based on either delayed fluorescence or phosphorescence are still limited and very hard to achieve simultaneously. Here, we report the design and synthesis of a new thermally activated delayed fluorescence emitter, 3Ph2CzCzBN. A sky-blue device based on 3Ph2CzCzBN exhibits a high external quantum efficiency of 16.6% at 1000 cd m−2. The device shows a sky-blue electroluminescence of 482 nm and achieves Commission Internationale de l’ Eclairage coordinates of (0.17, 0.36). The sky-blue device exhibits a superb LT90 of 38 h. This is the first demonstration of high-efficiency and stable sky-blue devices (CIEy < 0.4) based on delayed fluorescence, which represents an important advance in the field of blue organic light-emitting diode technology.

Near-IR organic light-emitting diodes (NIR-OLEDs) are potential light-sources for various sensing applications as OLEDs have unique features such as ultraflexibility and low-cost fabrication. However, the low external electroluminescence (EL) quantum efficiency (EQE) of NIR-OLEDs is a critical obstacle for potential applications. Here, we demonstrate a highly efficient NIR emitter with thermally activated delayed fluorescence (TADF) and its application to NIR-OLEDs. The NIR-TADF emitter, TPA-PZTCN, has a high photoluminescence quantum yield of over 40 % with a peak wavelength at 729 nm even in a highly doped codeposited film. The EL peak wavelength of the NIR-OLED is 734 nm with an EQE of 13.4 %, unprecedented among raremetal-free NIR-OLEDs in this spectral range. TPA-PZTCN can sensitize a deeper NIR fluorophore to achieve a peak wavelength of approximately 900 nm, resulting in an EQE of over 1 % in a TADF-sensitized NIR-OLED with high operational device durability (LT 95 > 600 h.).

A bio-inspired organic semiconductor 5,5 0-diphenylindigo shows excellent and well-balanced ambipolar transistor properties; its hole and electron mobilities are 0.56 and 0.95 cm 2 V À1 s À1 , respectively. The enhanced performance is attributed to the extended p-p overlap of the phenyl groups as well as the characteristic packing pattern that is a hybrid of the herringbone and brickwork structures. The ambipolar transistor characteristics are analyzed considering its operating regions, where a large unipolar saturated region appears due to the difference of the electron and hole threshold voltages. Scheme 1 Structures of indigo derivatives.