Ambipolar Phosphine Derivatives to Attain True Blue OLEDs with 6.5% EQE.
A family of new branched phosphine derivatives {Ph2N-(C6H4)n-}3P → E (E = O 1-3, n = 1-3; E = S 4-6, n = 1-3; E = Se 7-9, n = 1-3; E = AuC6F5 4-6, n = 1-3), which are the donor-acceptor type molecules, exhibit efficient deep blue room temperature fluorescence (λem = 403-483 nm in CH2Cl2 solution, λem = 400-469 nm in the solid state). Fine tuning the emission characteristics can be achieved varying the length of aromatic oligophenylene bridge -(C6H4)n-. The pyramidal geometry of central R3P → E fragment on the one hand disrupts π-conjugation between the branches to preserve blue luminescence and high triplet energy, while on the other hand provides amorphous materials to prevent excimer formation and fluorescence self-quenching. Hence, compounds 2, 3, 5, and 12 were used as emitters to fabricate nondoped and doped electroluminescent devices. The luminophore 2 (E = O, n = 2) demonstrates excellently balanced bipolar charge transport and good nondoped device performance with a maximum external quantum efficiency (EQEmax) of 3.3% at 250 cd/m(2) and Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.08). The doped device of 3 (E = O, n = 3) shows higher efficiency (EQEmax of 6.5, 6.0 at 100 cd/m(2)) and high color purity with CIE (0.15, 0.06) that matches the HDTV standard blue. The time-resolved electroluminescence measurement indicates that high efficiency of the device can be attributed to the triplet-triplet annihilation to enhance generation of singlet excitons.
University of Eastern Finland , Department of Chemistry, Joensuu 80101, Finland.
Ilya
I
Kondrasenko
Institute of Optoelectronic Sciences, National Taiwan Ocean University , Keelung 20224, Taiwan.
Zheng-Hua
ZH
Tsai
National Taiwan University , Department of Chemistry, Taipei 10617, Taiwan.
Kun-You
KY
Chung
Soochow University , Department of Chemistry, Lin-shih Rd. 70, Shih-Lin Taipei, TW 111, Taiwan.
Yi-Ting
YT
Chen
University of Eastern Finland , Department of Chemistry, Joensuu 80101, Finland.
Yana Yu
YY
Ershova
Universidad de Valencia , Dr. Moliner 50, 46100, Burjassot, Valencia Spain.
Antonio
A
Doménech-Carbó
Institute of Optoelectronic Sciences, National Taiwan Ocean University , Keelung 20224, Taiwan.
Wen-Yi
WY
Hung
National Taiwan University , Department of Chemistry, Taipei 10617, Taiwan.
Pi-Tai
PT
Chou
Aalto University , Department of Chemistry, FI-00076 Aalto, Finland.
Antti J
AJ
Karttunen
University of Eastern Finland , Department of Chemistry, Joensuu 80101, Finland.
Igor O
IO
Koshevoy
blue OLED; donor−acceptor molecules; electroluminescence; luminescent materials; phosphor-organic compounds