Efficient Triplet-Triplet Annihilation Upconversion in an Electroluminescence Device with a Fluorescent Sensitizer and a Triplet-Diffusion Singlet-Blocking Layer.

Solid-state triplet-triplet annihilation upconversion (TTAUC) blue emission in an electroluminescence device (i.e., an organic light-emitting diode (OLED)) is demonstrated. A conventional green fluorophore, tris-(8-hydroxyquinoline)aluminum (Alq ₃ ), is employed as the sensitizer that generates 75% triplet under electrical pumping for the blue triplet-triplet annihilation emitter, 9,10-bis(2'-naphthyl) anthracene (ADN), with the heterojunction bilayer structure. The operation lifetime is elongated both for ADN blue (4.1x) and Alq ₃ green (34.8%) emission due to efficient use of excitons and separation of recombination and emission zone. To reduce the singlet quenching (SQ) of blue TTAUC signal by the Alq ₃ sensitizer with lower bandgap, 1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene (DMPPP) is inserted between the Alq ₃ and ADN as a triplet-diffusion-and-singlet-blocking layer. DMPPP exhibits triplet energy close to Alq ₃ and higher than ADN, as well as higher singlet energy than both Alq ₃ and ADN. It allows triplet diffusion from Alq ₃ to ADN, but blocks the SQ of the blue TTAUC signal by Alq ₃ . 86.1% intrinsic efficiency of TTAUC is demonstrated in this trilayer (Alq ₃ /DMPPP/ADN) OLED.
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