Solution‐Processible Carbazole Dendrimers as Host Materials for Highly Efficient Phosphorescent Organic Light‐Emitting Diodes

Abstract

A group of dendrimers with oligo‐carbazole dendrons appended at 4,4′‐ positions of biphenyl core are synthesized for use as host materials for solution‐processible phosphorescent organic light‐emitting diodes (PHOLEDs). In comparison with the traditional small molecular host 4,4′‐N,N′‐dicarbazolebiphenyl (CBP), the dendritic conformation affords these materials extra merits including amorphous nature with extremely high glass transition temperatures (ca. 376 °C) and solution‐processibility, but inherent the identical triplet energies (2.60–2.62 eV). In comparison with the widely‐used polymeric host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (–5.61 to –5.42 eV) that facilitate efficient hole injection and are favorable for high power efficiency in OLEDs. The agreeable properties and the solution‐processibility of these dendrimers makes it possible to fabricate highly efficient PHOLEDs by spin coating with the dendimers as phosphorescent hosts. The green PHOLED containing Ir(ppy)3 (Hppy = 2‐phenyl‐pyridine) dopant exhibits high peak efficiencies of 38.71 cd A−1 and 15.69 lm W−1, which far exceed those of the control device with the PVK host (27.70 cd A−1 and 9.6 lm W−1) and are among the best results for solution‐processed green PHOLEDs ever reported. The versatility of these dendrimer hosts can be spread to orange PHOLEDs and high efficiencies of 32.22 cd A−1 and 20.23 lm W−1 are obtained, among the best ever reported for solution‐processed orange PHOLEDs.

Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices

“…1). For example, besides the function of coordinating to the central metal ions, 28,29 functional units containing nitrogen atoms can be used to enhance the hole injection/transporting (HI/HT) abilities [30][31][32] or electron injection/transporting (EI/ET) properties [33][34][35] of phosphorescent emitters and host materials depending on the different hybrid modes of the nitrogen atom. Thus, the design and synthesis of new phosphorescent emitters and their host materials represent two research focuses in the PHOLED field to improve the device performance.…”

Novel Ir(ppy)3 Derivatives: Simple Structure Modification Toward Nearly 30% External Quantum Efficiency in Phosphorescent Organic Light‐Emitting Diodes

“…The HOMO levels of these complexes were determined by the onset potentials of fi rst oxidation wave to be ≈−4.99, −5.04, −5.12, and −5.18 eV for 3F to 6F , respectively, showing the regular deepening with increasing F atom number. These shallow HOMO levels are quite close to the work function of ITO anode (−4.8 eV) and the HOMO of the most widely used hole injecting material PEDOT:PSS (−5.2 eV) [ 20 ] and should be favorable for direct hole trapping to facilitate the hole injecting into emitting layer and excitation of these iridium phosphor. By subtracting the optical band gaps obtained by absorption edge technique, [ 20 ] the LUMO levels were calculated as in the range of −2.38 to −2.43 eV.…”

Synthesis and Electroluminescence Properties of 3-(Trifluoromethyl)phenyl-Substituted 9,10-Diarylanthracene Derivatives for Blue Organic Light-Emitting Diodes

“…The quantum yields (Φ) of 1-3 were calculated as 0.24, 0.21 and 0.22, respectively, which are similar to each other (Table 1) 4 Calculated from the Eox. 5 Estimated from the HOMO and band-gap (Eg) energies. 6 Quantum yield measured using quinine sulfate as a standard (0.5 M H2SO4, Φ = 0.55) in CH2Cl2 (1.0 × 10 −5 M).…”

“…Extremely pure red, green, and blue luminophores with high electrochemical stability and efficiency are particularly essential for a vivid full-color display in organic light-emitting diodes (OLEDs). To date, OLED materials for red and green emission with high performance have been developed [3][4][5][6][7][8][9][10][11]. However, continuous efforts to enhance stability and efficiency in blue fluorescent materials, which possess relatively low chemical and electrochemical properties, caused by the intrinsic wide band-gap, are still required [12,13].…”