Exciplex-forming cohost systems with 2,7-dicyanofluorene acceptors for high efficiency red and deep-red OLEDs

• Published in: Scientific reports Vol. 14; no. 1; p. 2458
• Main Authors: Chen, Yi-Sheng, Lin, I-Hung, Huang, Hsin-Yuan, Liu, Shun-Wei, Hung, Wen-Yi, Wong, Ken-Tsung
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 30.01.2024; Nature Publishing Group UK; Nature Portfolio
• Subjects: Efficiency; Energy transfer; Photons
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-024-52680-6

Two 2,7-dicyaonfluorene-based molecules 27-DCN and 27-tDCN are utilized as acceptors (A) to combine with hexaphenylbenzene-centered donors (D) TATT and DDT-HPB for probing the exciplex formation. The photophysical characteristics reveal that the steric hindered 27-tDCN not only can increase the distance of D and A, resulting in a hypsochromic emission, but also dilute the concentration of triplet excitons to suppress non-radiative process. The 27-tDCN-based exciplex-forming blends exhibit better photoluminescence quantum yield (PLQY) as compared to those of 27-DCN-based pairs. In consequence, among these D:A blends, the device employing DDT-HPB:27-tDCN blend as the emissiom layer (EML) exhibits the best EQE of 3.0% with electroluminescence (EL) λ of 542 nm. To further utilize the exciton electrically generated in exciplex-forming system, two D-A-D-configurated fluorescence emitter DTPNT and DTPNBT are doped into the DDT-HPB:27-tDCN blend. The nice spectral overlap ensures fast and efficient Förster energy transfer (FRET) process between the exciplex-forming host and the fluorescent quests. The red device adopting DDT-HPB:27-tDCN:10 wt% DTPNT as the EML gives EL λ of 660 nm and maximum external quantum efficiency (EQE ) of 5.8%, while EL λ of 685 nm and EQE of 5.0% for the EML of DDT-HPB:27-tDCN:10 wt% DTPNBT. This work manifests a potential strategy to achieve high efficiency red and deep red OLED devices by incorporating the highly fluorescent emitters to extract the excitons generated by the exciplex-forming blend with bulky acceptor for suppressing non-radiative process.