Jiajia Luo

Multi-carbazole encapsulation as a simple strategy for the construction of solution-processed, non-doped thermally activated delayed fluorescence emitters

Two TADF emitters are developed via the introduction of carbazole dendrons into the multi-positions of a blue TADF emissive core. By utilizing these TADF emitters as the non-doped solution-processed emissive layers, the resulting greenish-blue OLED achieves a peak EQE of 12.2%, which is among the highest values for non-doped solution-processed fluorescent OLEDs.

Inheriting the Characteristics of TADF Small Molecule by Side‐Chain Engineering Strategy to Enable Bluish‐Green Polymers with High PLQYs up to 74% and External Quantum Efficiency over 16% in Light‐Emitting Diodes

Thermally activated delayed fluorescence (TADF) polymers are designed and synthesized by grafting the TADF emitter to the side chain of the polycarbazole backbone. By employing these TADF polymers with large ratio of delayed fluorescence component and high photoluminescence quantum yield as the emitters, the solution-processed light-emitting diodes achieve a maximal external quantum efficiency of 16.1% at a luminance of around 100 cd m-2 .

Asymmetric-triazine-cored triads as thermally activated delayed fluorescence emitters for high-efficiency yellow OLEDs with slow efficiency roll-off

Two yellow-emissive triads, DPXZ–as-TAZ and TPXZ–as-TAZ, featuring an asymmetric triazine (1,2,4-triazine) core as an electron acceptor, phenoxazine units as electron donors and phenyl groups as π-linkages are constructed. Both emitters possess high thermal stability, suitable HOMO/LUMO levels, relatively high PLQY, near-zero singlet–triplet energy splitting, apparent TADF features and short delayed lifetimes. As a result, a yellow OLED utilizing TPXZ–as-TAZ as an emitter reaches a maximum external quantum efficiency (EQE) of 13.0%, which is on a par with a similar device (13.3%) based on a symmetric-triazine (1,3,5-triazine) cored analogue. Surprisingly, a TPXZ–as-TAZ-based device exhibits a high EQE of 11.5% and an ultra-slow efficiency roll-off of 11.5% at a high luminance of 1000 cd m−2. For the first time, this work reports the huge potential of asymmetric triazine compounds as TADF emitters for high-performance OLEDs.

Halogen-induced internal heavy-atom effect shortening the emissive lifetime and improving the fluorescence efficiency of thermally activated delayed fluorescence emitters

Halogenation of an electron acceptor in TADF emitters is presented as a feasible strategy for shortening the DF lifetimes of TADF emitters without sacrificing their photoluminescence quantum yields. A greenish-yellow device based on the chloride-substituted emitter (ClPPM) achieves a high external quantum efficiency of 22.2% and an ultra-slow efficiency roll-off of 12.3% at a practical luminance of 1000 cd m−2, which is comparable to the state-of-the-art device performance for green-to-yellow TADF OLEDs at the practical luminance.

Tailoring the framework of organic small molecule semiconductors towards high-performance thermoelectric composites via conglutinated carbon nanotube webs

Recently, the thermoelectric (TE) properties of single-walled carbon nanotubes (SWCNTs)/polymer semiconductor composites have been dramatically improved; however, there are no examples of SWCNTs/organic small molecule semiconductor (OSMS) composites as TE materials, although OSMSs are more attractive due to their exact structure, easy structure optimization, high purity for performance optimization, etc. In this work, four p-type OSMSs are designed and synthesized as p-type binders for application in SWCNT-doped composite films. The relationship between TE properties and the structure including the conjugated-backbone and peripheral substituents is investigated. Photophysical spectroscopic and scanning electron microscopic studies indicate that the variation of molecular geometries and hybrid ratios results in obvious changes in the morphologies, interfacial contacts and grain boundaries of the composite films, subsequently affecting the TE properties of the samples. Notably, the SWCNT/TCzPy (1 : 1)-based hybrid film exhibits the best performance with an average power factor of 108.4 ± 4.8 μW m−1 K−2, which is three times higher than that of SWCNT/TDOPAPy. The results demonstrate that fine tuning the π-extensions of the central core or peripheral substituents of organic semiconductors is a good strategy for designing high-performance p-type organic small molecule TE materials.