Abstract
AbstractIt is generally recognized that hole‐transport layers (HTLs) with thickness on the order of tens nanometer are indispensable to high luminance and quantum efficiency in small molecule organic light‐emitting diodes (OLEDs). However, in this work, without conventional HTLs, a thin polytetrafluoroethylene (Teflon) layer was introduced as hole‐injection layer, followed by deposition of an emissive layer (EML), Alq3 doped with 0.7wt% DMQA. And simultaneously, a blocking and electron transport layer of aluminum (III) bis (2‐methyl‐8‐quinolinato) 4‐phenylphenolate (BAlq) ETL was employed to confine holes and excitons in Alq3 layer. The obtained OLEDs exhibited a luminance of over 88000 cd/m2 and external quantum efficiency of 5.4% (21.1 cd/A) at voltage of 19.8 V and current density of 418 mA/cm2. When the Teflon thickness was 10.0 nm under our conditions, well‐balanced charge injection could be obtained in OLEDs. It was also found that the high performance was related to triplet‐triple annihilation, in which triplet excited tris (8‐hydroxyquinoline) aluminum (3Alq3*) excitons go through annihilative reactions with other 3Alq3* excitons to form singlet excited molecules. It provides a new way of obtaining highly efficient and stable OLEDs with well‐balanced charge injection.
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