Thermally Activated Delayed Fluorescence Material as Host with Novel Spiro‐Based Skeleton for High Power Efficiency and Low Roll‐Off Blue and White Phosphorescent Devices

Abstract

7929wileyonlinelibrary.com external quantum efficiency (EQE) are two critical factors. [6][7][8][9][10] For green PhOLEDs, the devices with EQE over 25%, extremely low driving voltage below 3 V at luminance of 5000 cd m −2 , and low efficiency roll-off have been reported. [11,12] Nevertheless, for blue type, the PE still lags behind because of high driving voltage. Besides, large efficiency roll-off at high brightness (>1000 cd m −2 ), for which interfacial quenching effects like triplet-triplet annihilation (TTA) and/or triplet-polaron quench (TPQ) of host materials takes most responsibility, also remains a key issue for blue PhOLEDs. [13][14][15][16] Developing host materials to reduce singlet-triplet energy splitting (ΔE st ) is believed to be an effective solution. In this way, high triplet energy (T 1 ) to determine the effective host→guest energy transfer and relatively low singlet energy (S 1 ) to facilitate hole/electron injection can possibly make a good tradeoff [17][18][19][20] Until now, most of the reported hosts with small ΔE st generally follow donor-acceptor (D-A) construction because modulating donor/acceptor's strength and spatial overlap can relatively change S 1 and T 1 energy levels thus minimizing ΔE st . [21][22][23][24][25] For example, Duan et al. achieved a maximum EQE of 24.5% and PE of 64 lm W −1 in an orange PhOLED by using novel hosts with small ΔE st . [26] Besides, Wang et al. reported a maximum EQE of 15.6% and 11.8% in red and orange PhOLEDs based on a small ΔE st host material MTXSFCz. [27]However, so far, related researches are only limited in green, orange, or red PhOLEDs, with blue one being rarely studied. As the blue host with small ΔE st has stricter requirements for it calls for the highest T 1 energy among the RGB colors, while the T 1 energy is easily decreased along with the endeavor to reduce S 1 by varying organic groups. [28] To overcome this general problem, characteristics of relevant electronic energy transition should be understood. In such small ΔE st materials, some strongly localized states with 3 ππ* or 3 nπ* character are generally lower in energy than the 3 CT (CT: charge transfer) state, indicating that ΔE st can be reduced by adjusting the energy levels of the 1 CT state and the lowest locally excited triplet AbstractEfficiency roll-off in blue organic light-emitting diodes especially at high brightness still remains a vital issue for which the excitons densitydependent mechanism of host materials takes most responsibility. Additionally, the efficiency roll-off leads to high power consumption and reduces the operating lifetime because higher driving voltage and current are required. Here, by subtly modifying the triphenylamine to oxygen-bridged quasi-planar structure, a novel thermally activated delayed fluorescence type blue host Tri-o-2PO is successfully developed. Efficiency roll-off based on Tri-o-2PO is ultralow with external quantum efficiency (EQE) just dropping by around 2% in the high luminance range from 1000 cd m −2 to 10 000 cd m −2 . As expe...

Donor−σ–Acceptor Molecules for Green Thermally Activated Delayed Fluorescence by Spatially Approaching Spiro Conformation

“…It could be noted that other closed triphenylamine systems with sulfur or silicon atom as the bridge are also reported, but the merits of oxygen include stronger electron-donating ability because of the matched 2p lone-pair electrons and resistance for further oxidation. 14,22,26 As for another important factor, PLQYs of the target molecules were estimated with integration sphere (IS). OSTFCN and OSTFB showed moderate PLQY in toluene of 48% and 39%, respectively.…”

Pure Hydrocarbon Materials as Highly Efficient Host for White Phosphorescent Organic Light‐Emitting Diodes: A New Molecular Design Approach

“…The EMLs were exactly those used in the above‐mentionned PhOLEDs (15 wt % FIrpic) and display lifetimes of 1.26, 1.31 and 1.29 μs for 1‐mtp‐SBF, 1‐mbp‐SBF, and 1‐p‐SBF, respectively. Thus, the lifetime of the EML using 1‐mtp‐SBF is shorter than those of 1‐mbp‐SBF and 1‐p‐SBF, which might help to reduce the triplet density and the possibility of triplet–triplet annihilation (TTA) [63–67] . This feature is surely involved in the very high device performance obtained.…”

Thermally activated delayed fluorescence exciplexes with phosphor components realizing deep-red to near-infrared electroluminescence

“…To construct deep-red and NIR exciplex emitters in this work, a sky-blue phosphor Ir-817 with strong electron-donating ability was used as the donor. 29 Meanwhile, the classical electron-transporting materials (ETMs) B2PyMPM, B3PyMPM and B4PyMPM were chosen as acceptors, and their molecular structures are depicted in Fig. 1a.…”