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

Abstract

Since their introduction over 15 years ago, the operational lifetime of blue phosphorescent organic light-emitting diodes (PHOLEDs) has remained insufficient for their practical use in displays and lighting. Their short lifetime results from annihilation between high-energy excited states, producing energetically hot states (>6.0 eV) that lead to molecular dissociation. Here we introduce a strategy to avoid dissociative reactions by including a molecular hot excited state manager within the device emission layer. Hot excited states transfer to the manager and rapidly thermalize before damage is induced on the dopant or host. As a consequence, the managed blue PHOLED attains T80=334±5 h (time to 80% of the 1,000 cd m−2 initial luminance) with a chromaticity coordinate of (0.16, 0.31), corresponding to 3.6±0.1 times improvement in a lifetime compared to conventional, unmanaged devices. To our knowledge, this significant improvement results in the longest lifetime for such a blue PHOLED.

The Role of Reverse Intersystem Crossing Using a TADF‐Type Acceptor Molecule on the Device Stability of Exciplex‐Based Organic Light‐Emitting Diodes

“…At constant current density of 3.3 mA cm −2 , both devices (with and without ν‐DABNA) showed LT 50 over 300 h. Note that the initial luminance of the ν‐DABNA doped OLED (1260 cd m −2 ) is much higher than that of the non‐doped one (830 cd m −2 ). The blue OLED possessing high T 1 dopant (for example, T 1 of ν‐DABNA is 2.8 ± 0.05 eV) often suffers from low operational device stability due to a formation of hot excitons due to the large number of accumulated triplet states . However, this is not the case here since no reduction in LT 50 was observed, indicating that T 1 of ν‐DABNA did not undergo triplet accumulation inside the EML during OLED operation.…”

Bis‐Tridentate Iridium(III) Phosphors with Very High Photostability and Fabrication of Blue‐Emitting OLEDs

“…The use of this technology requires the employment of light‐emitting materials with three elementary colors, i.e., red, green, and blue. However, development of highly efficient and stable blue emitters remains demanding in comparison to green and red counterparts for which their lower energy gaps make them less susceptible to the formation of highly energetic, hot excited states generated by exciton–polaron and/or exciton–exciton annihilation 2. Although, certain pure organic thermally activated delay fluorescent (TADF) emitters have already showed satisfactory blue CIE x , y chromaticity,3 the long‐lived operational stability has not yet been achieved 4.…”

Mer‐Ir(ppy)3 to Fac‐Ir(ppy)3 Photoisomerization

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In this contribution a detailed mechanistic investigation of merto-fac photoisomerization occurring in Ir(ppy) 3 (ppy = 2-phenylpyridine) is presented. [3][4][5][6][7][8] Degradation of PhOLEDs' materials originates from parasitic exciton-polaron and exciton-exciton annihilation processes, [4,7] such as e. g., triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), which also compromise PhOLEDs efficiency at high brightness levels (i. e., roll-off effect). Double-hybrid density functional theory (DFT) calculations are performed herein to identify the photoactive species involved in the photoisomerization reaction and to assess its kinetic and thermodynamic feasibility at room temperature.

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