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Polycyclic heteroaromatics (PHAs) are a highly versatile class of functional materials, especially applicable as efficient luminophores in organic light-emitting diodes (OLEDs). Those constructed by tethered phenyl surrounding the main group center attract extensive attention due to their excellent OLED device performance. However, the development of such a class of emitters is often limited to boron, nitrogen-doped π-conjugated heterocycles. Herein, we proposed a novel kind of blue emitter by constructing a donor-acceptor molecular configuration, utilizing a dual sulfone-bridged triphenylamine (BTPO) core and mono/di-diphenylamine (DPA) substituents. The twisted D-A molecular structures and appropriate donor strength facilitate the effective separation of natural transition orbitals, endowing the emitters with charge-transfer dominant hybridized local and charge-transfer characteristics for the excited states. Both BTPO-DPA and BTPO-2DPA own small S 1 -T 1 splitting energy, thus demonstrating blue thermally activated delayed fluorescence. The more symmetrical structure and enhanced CT features brought by additional DPA moiety confer BTPO-2DPA with a shorter delayed fluorescence lifetime, a higher fluorescence quantum yield and narrower emission. Therefore, BTPO-2DPA based OLED devices exhibit superior blue electroluminescence performance, with external quantum efficiencies reaching 12.31 %., (© 2024 Wiley-VCH GmbH.)

Stability is one of the major challenges in organic semiconductor based optoelectronic devices. A comparative study of thermally activated delayed fluorescence (TADF) based organic light emitting diodes (OLEDs) with alkali-halide lithium fluoride (LiF) vs alkaline halide magnesium fluoride (MgF2) inorganic electron injection interlayers is presented. A TADF emitter 4CzIPN doped in CBP is used as an active layer (thickness = 15 nm @6wt. % doping) in an OLED structure: Glass/ITO/PEDOT:PSS/NPD/CBP/CBP:4CzIPN/TPBi/interlayer/Al. Prior to this comparative study, a separate exercise is carried out to obtain an optimal thickness of an MgF2 interlayer on the basis of leakage current and efficiency in the TADF-OLEDs. OLEDs with an LiF interlayer showed an external quantum efficiency (EQE) of 19.7% in comparison with an MgF2 interlayer-based OLED showed slightly lower average EQE ∼19.1% at a luminance level of 100 cd/m2; these efficiency numbers are averaged over ∼60 OLEDs. These slight changes in EQE are supported by the relative photoluminescence quantum yield measurements with a whole device stack. However, alkaline halide MgF2 based TADF-OLEDs showed approximately seven-fold enhancement in the stability (LT60) under identical operating conditions. In situ photoluminescence monitoring of operational TADF-OLEDs confirmed that the probable cause of reduced lifetime is degradation of an LiF/TPBi interface. [ABSTRACT FROM AUTHOR]

Polycyclic heteroaromatics (PHAs) are a highly versatile class of functional materials, especially applicable as efficient luminophores in organic light‐emitting diodes (OLEDs). Those constructed by tethered phenyl surrounding the main group center attract extensive attention due to their excellent OLED device performance. However, the development of such a class of emitters is often limited to boron, nitrogen‐doped π‐conjugated heterocycles. Herein, we proposed a novel kind of blue emitter by constructing a donor‐acceptor molecular configuration, utilizing a dual sulfone‐bridged triphenylamine (BTPO) core and mono/di‐diphenylamine (DPA) substituents. The twisted D−A molecular structures and appropriate donor strength facilitate the effective separation of natural transition orbitals, endowing the emitters with charge‐transfer dominant hybridized local and charge‐transfer characteristics for the excited states. Both BTPO‐DPA and BTPO‐2DPA own small S1–T1 splitting energy, thus demonstrating blue thermally activated delayed fluorescence. The more symmetrical structure and enhanced CT features brought by additional DPA moiety confer BTPO‐2DPA with a shorter delayed fluorescence lifetime, a higher fluorescence quantum yield and narrower emission. Therefore, BTPO‐2DPA based OLED devices exhibit superior blue electroluminescence performance, with external quantum efficiencies reaching 12.31 %. [ABSTRACT FROM AUTHOR]

Semiconductor junctions are among the most important material interfaces in modern technology. The solid polymer light‐emitting electrochemical cell (PLEC) possesses a semiconducting polymer homojunction that is reminiscent of a conventional p–n junction but also exhibits distinct features that are profoundly intriguing. The PLEC junction is formed under bias when the propagating p‐ and n‐doping fronts make contact. The PLEC junction can be immobilized by cooling after the initial junction formation. Further, the resulting frozen junction can be relaxed, or partially de‐doped into a p–i–n junction by controlled heating/cooling cycles. It is on such a frozen polymer p–i–n junction that the authors observed one of the most puzzling phenomena in organic electroluminescence (EL). The frozen p–i–n junction displays the brightest reverse bias (RB) EL ever imaged in a polymer junction and a large photovoltage. Moreover, the RB EL exhibits hypersensitivity to temperature, increasing in intensity by 22.6% K−1 when the de‐doped cell is cooled from 250 to 200 K. A model based on the tunnel injection of charge carriers with fast transit time across the intrinsic region explains the RB EL's hypersensitivity to temperature and super‐linear dependence on cell current. [ABSTRACT FROM AUTHOR]

We synthesized a polymer, poly(N,N′-diphenyl-N,N′-bis(4-methylphenyl)-1,4-phenylenediam ine1,3-diisopropenylbenzene) (PDAIPB), of which the energy of the highest occupied molecular orbital was measured to be 5.6 eV below vacuum level. In this article, PDAIPB was used as a hole transporter in a light emitting diode, with tri(8-hydroxyquinoline)-aluminum (Alq[sub 3]) as an electron transporter and emitting layer to ameliorate the stability of the device, and fullerene doped in the hole transporting layer as a sensitizer to study the influence of sensitizer on organic electroluminescence (EL). Internal EL quantum efficiency as high as 7.8% was obtained under an applied electric field of 1.2x10[sup 6] V/cm and doping fullerene concentration of 0.9 wt %. A function for EL quantum efficiency in terms of the dopant concentration is derived. The theoretical analysis is consistent with the experimental results. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]