Chiral Dicarbazole-Ditriarylamine Hole Transport Materials for Circularly Polarized Electroluminescence

Abstract

Circularly polarized organic light-emitting diodes (CP-OLEDs) hold significant promise for 3D displays owing to their ability to directly emit circularly polarized light. However, achieving multicolor circularly polarized electroluminescence requires synthesizing and separating luminescence enantiomers with different emission wavelengths, greatly increasing manufacturing complexity and costs. In contrast, chiral hole transport materials present a straightforward and versatile strategy for achieving various high-performance CP-OLEDs. In this work, two pairs of chiral hole transport materials, R/S-CzTPA and R/S-BuCzTPA, were synthesized using R/S-1,1′-binaphthyl-2,2′-diamine as a chiral precursor. These compounds also integrate carbazole and triarylamine functional groups, combining efficient hole transport properties with axial chirality. The hole mobility for R-CzTPA and R-BuCzTPA are measured as 5.63 × 10-5 and 2.72 × 10-6 cm2 V-1 s-1 (E = 0.4 MV cm-1), respectively. Additionally, these materials exhibit strong circularly polarized luminescence with dissymmetry factors (|glum|) of up to 5.7 × 10-3/2.5 × 10-3 in toluene and 3.6 × 10-3/1.9 × 10-3 in films, alongside excellent thermal stability. Notably, green CP-OLEDs are fabricated using R/S-CzTPA as the chiral hole transport layer and tris(2-phenylpyridine)iridium(III) as the achiral phosphorescent emitter, achieving the maximum luminance of 94449/93661 cd m-2, maximum current efficiency of 62/61 cd A-1, maximum external quantum efficiency of 19/18%, and electroluminescence dissymmetry factor of - 1.2 × 10-3/+ 1.6 × 10-3.