Bifunctional oligofluorene-cored carbazole dendrimers as solution-processed blue emitters and hole transporters for electroluminescent devices

Abstract

A series of bifunctional oligofluorene-cored carbazole dendrimers (GnFm, n = 1–3, m = 2–3) containing carbazole dendrons up to the third generation as end-caps were synthesized and characterized as non-doped solution-processed blue-light emitters and hole transporters for organic light-emitting diodes (OLEDs). Their optical, thermal, electrochemical, and electroluminescence properties were investigated. They exhibited a strong deep-blue fluorescence with solution fluorescence quantum yields (Φ_F) of around 0.91–0.99 and formed morphologically stable amorphous thin films with glass transition temperatures as high as 273 °C. As blue emitters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/BCP/LiF:Al displayed a deep-blue emission (λ^EL_em = 415 nm, CIE = 0.17, 0.11) with a maximum luminance efficiency as high as 3.79 cd A⁻¹ and a low turn-on voltage of 4.2 V. As hole transporters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/Alq3/LiF:Al showed a bright green emission (λ^EL_em = 520 nm, CIE = 0.30, 0.54) with a maximum luminance efficiency as high as 5.63 cd A⁻¹ and a low turn-on voltage of 2.4 V.