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...

Blue Thermally Activated Delayed Fluorescence‐Emitting Phosphine Oxide Hosts for Ultrasimple and Highly Efficient White Organic Light‐Emitting Diodes

“…According to the number of emissive layers (EMLs), complementary WOLEDs can be divided into dual‐EML ( I and II ) and single‐EML ( III and IV ) types, in which the former takes use of spatial effect and energy level optimization on exciton allocation to achieve stable and efficient white EL at the cost of complicated structures, while the simpler latter suffers from volatile and turbulent charge transfer (CT) and ET processes ( Scheme a). Obviously, IV ‐type EML as yellow emitter‐doped blue emitting host can provide the most concise EL process, embodied as the rational exciton allocation on its two components.…”

CN‐Modified Imidazopyridine as a New Electron Accepting Unit of Thermally Activated Delayed Fluorescent Emitters

“…[18][19][20][21][22][23] In the last several years,a number of organic molecules with different electron-donating and -accepting groups bridged by a p-linker and/or s-spacer have been reported to exhibit TADF properties. [24,25] Electrondonating moieties such as carbazole,t riphenylamine, acridine, phenoxazine, phenazine, [26][27][28][29][30] and acceptorm oieties including triazine, pyrimidine, ketone, sulfone, phosphine oxide, dicyanobenzene, pyridine, and triarylboron [31][32][33][34][35][36][37] have been employed as successfuld onors/acceptors in efficientT ADF molecular emitter designs. However,f or their commercial application, TADF emitterss till requiren ew designs for efficient donor/acceptorm oieties with improved RISC processes.…”

Cyclization of Terphenyl‐Bisfluorenols: A Mechanistic Study of the Regioselectvity

“…For the last thirty years of research in material science, spirobifluorene-based compounds have been extensively studied for applicationsi no rganic electronicsa nd especially in organic light-emitting diodes (OLED). [1][2][3] The incorporation of spiro linkagesi ns mall molecular units is nowadays ap owerful molecular technique to design efficient and stable organic semiconductors:f luorophores for OLEDs, [3][4][5][6][7][8] high-triplet host materials forp hosphorescent OLEDs, [2,[9][10][11][12] thermally activated delayed fluorescenceh osts, [13][14][15] and electron-donor [16][17][18] or nonfullerenea cceptors [19][20][21][22] for solar cells. The spirobifluorenef ragment combines the physical advantages of an orthogonal spiro configuration (high thermala nd morphological stability) and the appealing properties of the fluorene unit (e.g.…”