P-161: 89.3% Lifetime Elongation of Blue TTA-OLED with Assistant Host

Abstract

Operation lifetime of a blue OLED exhibiting triplet-triplet annihilation increased by 89.3% with the incorporation of 10% assistant host in the emitting layer, which increased diffusion length of singlet exciton, reduced the quenching of triplet exciton, and blocked the triplet pair diffusion. Author Keywordsorganic light-emitting diode, lifetime, TTA, OLED Stability and Degradation Mechanisms Objective and BackgroundOrganic light-emitting diode (OLED) is a promising lighting and display technology [1]. Contrary to red and green OLEDs based on phosphorescent emitter which exhibit high efficiency and long lifetime, fluorescent emitter with triplet-triplet annihilation (TTA) characteristics is typically used for commercial blue OLED, and it results in lower efficiency and shorter lifetime [1]. Emission of TTA-OLED from singlets and triplets can be separated from turnoff dynamics of transient electroluminescence (TrEL) measurement due to the delayed emission of triplets [1]. To improve the lifetime of an OLED, a common strategy is to widen the emission zone. By mixing the hole-and electron-transporting materials to form a bipolar emitting layer (EML), recombination zone is extended and hence increases the operation lifetime [2]. Besides, emission zone can be also achieved by increasing the exciton diffusion length.In this paper, we co-evaporated an assistant host (AH) with volume concentration of 10% into the EML of a TTA-blue OLED, it was found that operation lifetime increased by 89.3% (measurement condition: T95@ 2000 cd/m2, which meant the required time for OLED luminance decreased to 95% of its initial value (2000 cd/m2) with constant current driving). This AH and the TTA host exhibited hole-and electron-transporting characteristic, respectively. However, we did not observe the recombination zone broadening. On the other hand, singlet and triplet exciton energy of AH were higher than that of TTA host. And we did observe the diffusion length of singlet exciton increased by 24.3% due to the dilution effect [3]. After electrical aging, triplet exciton experienced less quenching with the incorporation of AH. Besides, it also decreased the quenching of intermediate triplet pair. ExperimentsIn our blue OLED, TTA material was used as the host of the EML, with the incorporation of 4% blue dopant material. Concentration of AH was 0% and 10% in the EML for the two devices used in this paper, respectively. EML was sandwiched by hole-and electron-transporting layer (HTL and ETL). Indium-tin oxide (ITO) and Al was used as the anode and cathode, respectively. 20-nm thin film consisting of the host material of the EML with and without AH was deposited on the glass substrate and 50-nm C60 upon glass substrate, respectively, for obtaining the diffusion length. C60 here was used as a stronger exciton quencher. By comparing the photoluminescence (PL) intensity with and without quencher (C60), diffusion length can be obtained. Steady-state electroluminescence (EL) and spectrum was obtained by spectrometer (Minolta CS1000)...

Hot excited state management for long-lived blue phosphorescent organic light-emitting diodes

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P‐174: 16.1‐times Elongation of Operation Lifetime in a Blue TTA‐OLED by using New ETL and EML Materials

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TADF versus TTA emission mechanisms in acridan and carbazole-substituted dibenzo[a,c]phenazines: Towards triplet harvesting emitters and hosts

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