Red Electrophosphorescence from a Soluble Binaphthol Derivative as Host and Iridium Complex as Guest

Abstract

The investigation of the optical properties, carrier injection, and transport into a soluble small molecule, 6,6'-dicarbazolyl-2,2'-dihexyloxy-1,1'-binaphthol (BA), was reported. The results demonstrated that BA is a blue-emitting molecule, which can be used as a host for the fabrication of electrophosphorescent light-emitting diodes (LEDs). The single-layer electrophosphorescent LEDs fabricated from toluene solution containing BA with tris[2,5-bis-2'-(9',9'-dihexylfluorene)pyridine-kappa(2)NC(3)(')]iridium(III) [Ir(HFP)(3)] emitted red light from Ir(HFP)(3) triplet emission. The results from photoluminescence (PL) and electroluminescence (EL) demonstrated that the dominated operational mechanism in EL was charge trapping rather than Förster transfer, which was the dominated mechanism in PL. The single-layer OLEDs with 1wt % of Ir(HFP)(3) have a luminance (L) of 1000 cd/m(2) at 22 V and a luminous efficiency (LE) of 0.88 cd/A at 11 mA/cm(2). Double-layer electrophosphorescent LEDs fabricated by casting the emitting layer from a solution of BA blended with Ir(HFP)(3) and subsequently thermally depositing tris(8-hydroxyquinoline) aluminum (Alq(3)) film as an electron injection and transport layer yielded L = 1830 cd/m(2) at 30 V and LE = 2.47 cd/A at 18 mA/cm(2). These results demonstrated that electrophosphorescent LEDs can be fabricated from BA via solution processing and that L and LE can be enhanced by changing the device architecture with the goal of better balancing the electron and hole currents.

Spin‐Coated Highly Efficient Phosphorescent Organic Light‐Emitting Diodes Based on Bipolar Triphenylamine‐Benzimidazole Derivatives

“…The spin-coated DM-TIBN device exhibited the best performances with a maximum luminance of 47 500 cd m À2 , current efficiency of 27.3 cd A À1 , and maximum power efficiency of 7.3 lm W À1 , respectively, which is much better than for spin-coated Me-TIBN (39 000 cd m À2 , 14.6 cd A À1 , 3.7 lm W À1 ) and TIBN (1700 cd m À2 , 0.64 cd A À1 , 0.27 lm W À1 ). To the best of our knowledge, this performance is highly outstanding with respect to other seminal work ever reported for solution-processed OLEDs, such as those reported by the groups of Ding (7840 cd m À2 , 34.7 cd A À1 ), [30] Lo (18 500 cd m À2 , 30 cd A À1 ), [31] and Gong (1000 cd m À2 , 0.88 cd A À1 ), [32] and others.…”

Solution processable small molecules for organic light-emitting diodes

“…Gong et al reported small-moleculesbased OLEDs using a binaphthol derivative as host and redemitting Ir(HFP) 3 as guest by a solution process, achieving a maximum luminous efficiency of 0.88 cd A À1 for single layer devices and of 2.47 cd A À1 for double layer devices with an electron-transporting layer Alq 3 by thermal vapor deposition. 80 Fig. 8 Molecular structures of host materials.…”

Highly efficient solution-processed green and red electrophosphorescent devices enabled by small-molecule bipolar host material

“…In contrast, small molecules have exact molecular structure and can be easily purified to overcome the shortcomings of polymeric PhOLEDs. 20,21 Therefore it is of important significance to develop highly efficient small-molecule based PhOLEDs by solution-processing. 22,23 Due to the relatively long excited state lifetimes of triplet emitters, the heavy metal complexes are usually doped into host materials to reduce the self-quenching and triplet-triplet annihilation.…”