Xiaofang Wei

Highly Efficient Orange and Red Phosphorescent Organic Light‐Emitting Diodes with Low Roll‐Off of Efficiency using a Novel Thermally Activated Delayed Fluorescence Material as Host

MTXSFCz with thermally activated delayed fluorescence is synthesized. Orange and red phosphorescent organic light-emitting diodes (PHOLEDs) with low efficiency roll-off exhibit external quantum efficiencies (EQE) up to 11.8% and 15.6%. The efficient upconversion from triplet to singlet of the host reduces the triplet density and thus affords a low efficiency roll-off of PHOLEDs.

Aromatic Imide Based Thermally Activated Delayed Fluorescence Materials for Highly Efficient Organic Light Emitting Diodes

Aromatic-imide-based thermally activated delayed fluorescence (TADF) materials with a twisted donor-acceptor-donor skeleton were efficiently synthesized and exhibited excellent thermal stability and high photoluminescence quantum yields. The small ΔEST value (<0.1 eV) along with the clear temperature-dependent delayed component of their transient photoluminescence (PL) spectra demonstrated their excellent TADF properties. Moreover, the performance of organic light-emitting diodes in which TADF materials AI-Cz and AI-TBCz were used as dopants were outstanding, with external quantum efficiencies up to 23.2 and 21.1 %, respectively.

Highly Efficient Nondoped Organic Light Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitter with Quantum-Well Structure

Highly efficiency nondoped thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs) with multiquantum wells structure were demonstrated. By using an emitting layer with seven quantum wells, the nondoped TADF OLEDs exhibit high efficiency with EQE of 22.6%, a current efficiency of 69 cd/A, and a power efficiency of 50 lm/W, which are higher than those of the conventional doped OLED and among the best of the TADF OLEDs. The high performance of the devices can be ascribed to effective confinement of the charges and excitons in the emission layer by the quantum well structure. The emission layer with multiquantum well structure is demonstrated to be cost effective for highly efficient nondoped TADF OLEDs and holds great potential for organic electronics.

Reduction of the singlet–triplet energy gap of a thermally activated delayed fluorescence emitter by molecular interaction between the host and the emitter

We reported the comparative effect of 1,3-bis(9H-carbazol-9-yl) benzene (mCP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) hosts on the PL characteristics of 2-phenyl-4′-carbazole-9H-thioxanthen-9-one-10,10-dioxide (TXO-PhCz). Strong interaction between TXO-PhCz and TPBI can be observed, leading to the lower singlet–triplet energy gap of 8.8 meV and non-monotonic increase of ΦTotle, ΦD, and ΦP with temperature. OLEDs based on TXO-PhCz:TPBI films afford a maximum current efficiency of 71.9 cd A−1, a maximum power efficiency of 45.2 lm W−1, and a maximum EQE of 23.2%.

Highly efficient white light-emitting diodes with a bi-component emitting layer based on blue and yellow thermally activated delayed fluorescence emitters

Herein, highly efficient white light-emitting diodes with a bi-component light emitting layer of the blue TADF emitter 2′-(dimesitylboranyl)-N,N-diphenyl-[1,1′-biphenyl]-2-amine (o,o′-NPh2) and the yellow TADF emitter 4-phenyl-4′-carbazole-9-H-thioxanthen-9-one-10,10-dioxide (TXO-PhCz4) is reported, providing white light emission with a CIE of (0.38, 0.40), a high CRI of 71, and a maximum EQE of 12.5%, which is among the best of WOLEDs with a bi-component emitting layer.

Triplet decay-induced negative temperature dependence of the transient photoluminescence decay of thermally activated delayed fluorescence emitter

The photophysical properties of three TX-based D–A isomers (TXO-PhCz1, TXO-PhCz3, and TXO-PhCz4) with a PhCz donor at different substitution positions of phenyl group on a TXO unit were investigated. The substitution position of the PhCz unit significantly impacts the photophysical properties of these isomers. TXO-PhCz1 exhibits a very weak emission in both undoped and doped films, while TXO-PhCz3 and TXO-PhCz4 exhibit a strong emission with the requisite properties for TADF emitters, including a small ΔEST and transient PL decay curves with a prompt and delayed fluorescent component. TXO-PhCz4 exhibits a much stronger orbital coupling than TXO-PhCz3 and then the phosphorescent emission causes the inverse temperature dependence of the transient PL decay, which is contrary to that of TXO-PhCz3 and other TADF emitters. TXO-PhCz4 exhibits a small ΔEST of 23 meV and a short decay time of 14 μs at room temperature, which are much smaller and shorter than those of TXO-PhCz3. Multilayer OLEDs based on TXO-PhCz4 exhibit a very low-efficiency roll-off with a maximum current efficiency of 49.2 cd A−1, a maximum power efficiency of 47.7 lm W−1, and a maximum EQE of 16.3%.

n-Doping-induced efficient electron-injection for high efficiency inverted organic light-emitting diodes based on thermally activated delayed fluorescence emitter

High-performance inverted organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters are achieved using solution-processing n-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) film with cesium carbonate (Cs2CO3) as the buffer layer between ZnO and BPhen layer. The n-doped BPhen interlayer shows better electron-transporting properties than undoped BPhen film and reduces the electron-injection barrier from ZnO to BPhen layer. The inverted OLEDs, based on TXO-PhCz emitter incorporating the solution-processed Cs2CO3-doped BPhen film as an interlayer, show a maximum external quantum efficiency of 16.4%, current efficiency of 53.9 cd A−1, and power efficiency of 35.6 lm W−1, which realize unprecedentedly high-efficiency TADF-based inverted OLEDs. These results are competitive with the properties of inverted OLEDs based on phosphorescent emitters, implying that TADF emitters have potential to substitute for phosphors on realizing air-stable and large-area displays.

CCDC 1543551: Experimental Crystal Structure Determination

Related Article: Meng Li, Yanwei Liu, Ruihong Duan, Xiaofang Wei, Yuanping Yi, Ying Wang, Chuan-Feng Chen|2017|Angew.Chem.,Int.Ed.|56|8818|doi:10.1002/anie.201704435