Hole Mobilities of 2,7- and 2,2′-Disubstituted 9,9′-Spirobifluorene-Based Triaryldiamines and Their Application as Hole Transport Materials in OLEDs

Abstract

Hole mobilities of up to 2 × 10 -3 cm 2 V -1 s -1 of 2,7-and 2,2′-disubstituted spirobifluorene-based triaryldiamine derivatives have been measured using time-of-flight (TOF) techniques. Among these derivatives, 27DPSF (possessing diphenylamino groups attached onto the same biphenyl branch of spirobifluorene) and 22DPASF (possessing extended π-conjugation of the chromophore) exhibited the highest hole mobilities because of their greater intermolecular interactions. The charge transport parameters were extracted, using a Gaussian disorder model (GDM), from detailed temperature-and field-dependent hole mobility measurements. For 2,2′-disubstituted systems possessing different diarylamino groups, the hole mobilities decreased in the order 22DPSF > 22DTSF > 22DBPSF, indicating that spatial hindrance had a crucial effect on the hole transport behavior. To verify these disubstituted spirobifluorene-based amines can be used as HTLs in OLED devices. A standard device was fabricated with the configuration ITO/m-MTDATA (20 nm)/triaryldiamine derivative (40 nm)/Alq 3 (60 nm)/LiF (0.5 nm)/Al (150 nm), which gave a relatively high current density (ca. 5200 mA/cm 2 ), impressive maximum brightness (1.3 × 10 5 cd/m 2 ), and high external quantum efficiency (1.8%). The device performances are strongly correlated to the charge transporting behavior of such disubstituted spirobifluorene-based amines.

Multifunctional Fluorene‐Based Oligomers with Novel Spiro‐Annulated Triarylamine: Efficient, Stable Deep‐Blue Electroluminescence, Good Hole Injection, and Transporting Materials with Very High Tg

“…However, the hole mobility in NPB is about 2 orders of magnitude higher than the electron mobility in Alq 3 , which usually creates recombination areas near the emitting‐layer/cathode interface, and thus decreases the device efficiency 53. As compared to NPB, the conjugation of two triphenylamine group on DFSTPA is interrupted by the spiro‐linkage, and the orthogonal configuration in the spiro‐structure could increase the carrier hopping distance, and consequently decrease the hole mobility,54 which may result in a better balance between the electron and hole fluxes when DFSTPA acts as both hole‐injection and ‐transporting material.…”

Utilizing a Spiro Core with Acridine- and Phenothiazine-Based New Hole Transporting Materials for Highly Efficient Green Phosphorescent Organic Light-Emitting Diodes

“…spirobifluorene was one of the key molecules to achieve high efficiencies with stable morphological properties through modification at both the second and seventh positions by incorporating different electron-donating derivatives. Moreover, spiro molecules provide a rigid core along with a twisted structure at the ninth position of the fluorene unit [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Spiro-annulated molecules are connected with two conjugated moieties by a tetrahedral bonding atom, which minimizes the close stacking of molecules and enhances the rigidity of the core [ 26 ].…”

Ethanol‐promoted reductive homocoupling reactions of aryl halides catalyzed by palladium on carbon (Pd/C)

“…Biaryls and their heteroaromatic analogues have specific physicochemical properties which are widely used in the synthesis of conductive polymers, liquid crystals and important biaryl natural products 1–3. The Ullmann reductive homocoupling reactions of aromatic halides have been widely used to synthesize symmetrical biaryls (Scheme ) 4.…”