Abstract
Heptazine derivatives have attracted much attention over the past decade by virtue of intriguing optical, photocatalytic as well as electronic properties in the fields of hydrogen evolution, organic optoelectronic technologies and so forth. Here, we report a simple π-conjugated heptazine derivative (HAP-3DF) possessing an n→π* transition character which exhibits enhanced electroluminescence by exploiting thermally activated delayed fluorescence (TADF). Green-emitting HAP-3DF shows relatively low photoluminescence quantum efficiencies (Φ p) of 0.08 in toluene and 0.16 in doped film with bis(2-(diphenylphosphino)phenyl) ether oxide (DPEPO) as the matrix. Interestingly, the organic light-emitting diode (OLED) incorporating 8 wt% HAP-3DF:DPEPO as an emitting layer achieved a high external quantum efficiency (EQE) of 3.0% in view of the fairly low Φ p of 0.16, indicating the presence of TADF stemming from n→π* transitions. As the matrix changing from DPEPO to 1,3-di (9H-carbazol-9-yl)benzene (mCP), a much higher Φ p of 0.56 was found in doped film accompanying yellow emission. More importantly, enhanced electroluminescence was observed from the OLED containing 8 wt% HAP-3DF:mCP as an emitting layer, and a rather high EQE of 10.8% along with a low roll-off was realized, which should be ascribed to the TADF process deriving from exciplex formation.
Highlights
Organic light-emitting diodes (OLEDs) have received numerous attentions and experienced rapid development in the fields of display and lighting in view of extremely fascinating advantages such as flexibility, thinness, fast response (Im et al, 2017; Choi et al, 2018; Fukagawa et al, 2018)
Enhanced EL was observed from the OLED containing 8 wt% HAP-3DF:mCP as an emitting layer, and a rather high external quantum efficiency (EQE) of 10.8% along with a low roll-off was realized, which should be assigned to the thermally activated delayed fluorescence (TADF) process deriving from exciplex formation
The highest occupied molecular orbital (HOMO) is mainly distributed over the sp2hybridized N atoms in the heptazine core while the lowest unoccupied molecular orbital (LUMO) spreads to the whole π-conjugated system, which is in accordance with the character of n→π* transition
Summary
Organic light-emitting diodes (OLEDs) have received numerous attentions and experienced rapid development in the fields of display and lighting in view of extremely fascinating advantages such as flexibility, thinness, fast response (Im et al, 2017; Choi et al, 2018; Fukagawa et al, 2018). We report a π-conjugated heptazine derivative, 2,5,8-tris(2,4-difluorophenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (HAP-3DF), which exhibits enhanced EL by exploiting n→π* transitions and exciplex-based TADF, respectively. The OLED incorporating 8 wt% HAP-3DF:DPEPO as an emitting layer achieved a high maximum external quantum efficiency (EQE) of 3.0% in comparison to the fairly low photoluminescence quantum efficiency (Φp) of 0.16, indicating the presence of TADF stemming from n→π* transitions. To realize exciplexbased TADF, 1,3-di (9H-carbazol-9-yl)benzene (mCP) with two electron-donating carbazole moieties was chosen as the electrondonating material for HAP-3DF. Enhanced EL was observed from the OLED containing 8 wt% HAP-3DF:mCP as an emitting layer, and a rather high EQE of 10.8% along with a low roll-off was realized, which should be assigned to the TADF process deriving from exciplex formation.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
