High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence

Abstract

Blue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light-emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency (EQE) of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m−2. Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures.

Intermolecular TADF: bulk and interface exciplexes

“…In 2021, Vasilopoulou et al used the DBFPO/TSPO1 interface exciplex with the highly efficient HTM T2fQ to confine the excitons at the EML/ETM interface, thereby avoiding the adverse effect of the low E T value of HTM on the device efficiency, and the maximum EQE of the blue device reached 41.2%. 69 DBFPO is bis(diphenylphosphine oxide)dibenzofuran and TSPO1 is diphenyl [4-(triphenylsilyl) phenyl]phosphineoxide. The device performance of interface exciplexes is summarized in Table 4.…”

Discs to a ‘Bright’ Future: Exploring Discotic Liquid Crystals in Organic Light Emitting Diodes in the Era of New‐Age Smart Materials

“…Following the first report on TADF, rapid and exponential progress has been made towards developing highly efficient OLEDs with the current state of the art TADF OLEDs reaching up to 42 % presently. [46] Hybridized local charge transfer (HLCT) is another strategy for harvesting triplet excitons whereby, the triplet hot excitons (T m , where m > 2) (the excitons in higher energy state called hot excitons) are transferred to singlet higher state through reverse intersystem crossing. For efficient exciton utilization the energy gap between T m and T 1 state should be large so that internal conversion is restricted and the energy gap between T m and higher singlet state (S n , where n � 1) should be small so that efficient RISC occurs.…”

“…The smaller ΔE ST of 0.11 eV was observed due to twisted donor‐acceptor structure which led to small orbital overlap and high EQE of 5.3 % was observed. Following the first report on TADF, rapid and exponential progress has been made towards developing highly efficient OLEDs with the current state of the art TADF OLEDs reaching up to 42 % presently [46] . Hybridized local charge transfer (HLCT) is another strategy for harvesting triplet excitons whereby, the triplet hot excitons (T m , where m >2) (the excitons in higher energy state called hot excitons) are transferred to singlet higher state through reverse intersystem crossing.…”

Scope of Tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the Synthesis of Triazoloquinoxalines, Imidazoloquinoxalines, and Rhenium-complexes thereof

“…[5] Quinoxalines can also be used in organic solar cell polymers [1,6] and have been described as donor moieties in many TADF and OLED compounds. [7][8][9] Amongst many other possible ways to modify and extend the core structure of quinoxalines, the conversion of tetrazolo [1,5-a]quinoxalines offers several advantages, as tetrazolo [1,5-a]quinoxalines can be used as quinoxaline-azide precursor, serving as a precursor for new nitrogen-enriched quinoxaline-based structures. Literature-known procedures for such a quinoxaline modification starting from tetrazolo [1,5-a]quinoxalines 1 are the synthesis of 1,2,3-triazoloquinoxalines (3) via copper-catalyzed azide-alkyne cycloaddition (CuAAC) [10] and the synthesis of imidazo[1,2-a]quinoxalines (2), which was recently reported for the first time using tetraphenylporphyrin iron(III) chloride as a catalyst.…”

“…triazoloimidazoquinoxalines (TIQs): 2.5 equiv. hexyne, 10 mol% (CuOTf)2•C6H6(7), toluene, 100 °C, 4 h -3 d. ORTEP drawing of triazoloimidazoquinoxaline 25b with 50% probability.…”