Solution-processable organic light-emitting diodes utilizing electroluminescent perylene tetraester-based columnar liquid crystals

Abstract

Herein, we reveal a homologous series of liquid crystals involving perylene tetraesters as the core connected to the four trialkoxyphenyl units at the periphery using the triazole moiety as the linker. A thorough analysis using differential scanning calorimetry, polarized optical microscopy, and small- and wide-angle X-ray scattering studies confirm that all the mesogens 1a–c hold a stable enantiotropic columnar mesophase. Suitable molecular orbital levels and excellent material photophysical and thermal properties encouraged the study of their electroluminescent properties. Due to this, a well designed solution-processable organic light emitting diode device structure is configured as ITO (125 nm)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (35 nm)/host: x wt% emitter (x = 0.5, 1.0, 3.0, 5.0) (20 nm)/2,2′2′′-(1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) (40 nm)/lithium fluoride (LiF) (1 nm)/aluminium (Al) (200 nm) using compounds 1a–c as emitters. 4,4′,4′′-Tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) and 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) were chosen as two different host materials. The current density–voltage–luminance and current efficacy–luminance–power efficacy plots suggest that m-MTDATA is a better host than CBP. Amongst, device based on 1 wt% emitter 1c doped in the m-MTDATA host matrix displayed the best performance, with a maximum power efficacy of 17.2 lm W⁻¹, current efficacy of 18.5 cd A⁻¹, and external quantum efficiency of 6.3%.